Impact of Pilot Zones for Green Finance Reform and Innovations on green technology innovations: evidence from Chinese manufacturing corporates

Green technology innovation is a crucial factor in the global quest for sustainability. In 2017, China approved the establishment of Pilot Zones for Green Financial Reform and Innovations to build and improve the green financial system. Using a difference-in-difference (DID) model, this paper examines the impact of this pilot policy on corporate green technology innovation and its transmission mechanism based on the data of green patents of Chinese A-share listed manufacturing companies between 2014 and 2019. It is found that Pilot Zones for Green Financial Reform and Innovations have contributed to the growth of green technology innovations. This conclusion is confirmed after a series of robustness tests. The pilot policy’s promotion of green technology innovations is mainly reflected in the application of corporate green invention patents. However, it is more significant for non-heavy polluting enterprises, high-tech certified enterprises, and large enterprises. The paper also finds that the pilot policy promotes corporate green technology innovation by promoting social financing, talent support, and government financial support.


Introduction
China's ecological and environmental treatment and restoration have achieved some results due to the in-depth promotion of pollution prevention and control. To further improve environmental quality thereby establishing a link between environmental policies, economic instruments, and technology innovation, the focus of ecological governance at this stage is to develop innovative industrial green transformation through science and technology. In the post-pandemic era, a global consensus emerged to accelerate green development and promote industrial transformation. In 2020, China proposed to achieve peak carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060. In furtherance of its goals of carbon peaking and carbon neutrality, China implemented various environmental policies to achieve sustainable development. Although green finance in China started late, it is developing rapidly. To build and improve the green financial system, China is deeply engaged in green financial reform and innovation. In June 2017, the State Council of China built the first batch of Pilot Zones for Green Financial Reform and Innovations in five regions: Zhejiang, Jiangxi, Guangdong, Guizhou, and Xinjiang to promote green economic transformation and upgrading.
Corporates are seen as major drivers of economic development, but the growth of economic gains for corporates has also brought serious ecological problems. As major polluters and consumers of energy, corporates need to respond positively to environmental issues. From the corporates' perspectives, green technology innovation can help corporates achieve a lasting competitive advantage and have an essential impact on sustainable development. Therefore, green technology innovation is crucial for linking energyintensive production and sustainable development. From the perspective of the government, local governments also need to incentivize or require the green technology innovation Responsible Editor: Nicholas Apergis behavior of corporates through policy regulations, so as to promote regional green development. The policy of Pilot Zones for Green Finance Reform and Innovations explicitly calls on guiding financial institutions to support the green development of the manufacturing industry. Consequently, green finance plays a crucial role in the green transformation and upgrading of manufacturing enterprises.
As an important force in promoting the green transformation and upgrading of industries and achieving green and sustainable development, it is important to study the impact of the green financial reform and innovation pilot policy on corporate green technology innovation and to assess the specific effects of the policy on the real economy in terms of financial demand. Thus, this paper uses a sample of A-share listed manufacturing companies in China between 2014 and 2019 to examine whether the Pilot Zones for Green Finance Reform and Innovations have promoted corporate green technology innovation. It is found that the Pilot Zones for Green Finance Reform and Innovations have significantly enhanced the development of green technology innovations of regional corporates, especially in green invention patents. Furthermore, it is found that the pilot policy has a more significant positive impact on green technology innovation in non-heavy polluting enterprises, high-tech certified enterprises, and large enterprises. From the perspective of transmission mechanism, this paper finds that the pilot policy has a certain impact on local government behavior and promotes the green technology innovation of local corporates through social financing, talent support, and government financial support. Compared with similar studies that focus on the role of corporate behavior in the implementation of the policies, this paper pays more attention to the importance of local government behavior in the process of policy transmission. The Pilot Zones for Green Finance Reform and Innovations implement different green schemes with regional characteristics in five regions of China, which gives local governments a high degree of freedom in policy implementation. In this context, local governments' behaviors play an important intermediary role in the process of realizing policy effects. Based on this perspective, this paper can explore the mediating effect of government behavior in this pilot policy and provide empirical experience for local governments to implement relevant policies.

Literature review
Environmental regulation Cleff and Rennings (2000) defined environmental regulation as the push and pull role of government use of the policy of regulation. For Frondel et al. (2007), environmental regulation is a specific tool for government environmental policy implementation. Thus, environmental regulation is closely linked to environmental policy. In the classification of environmental regulatory policies, the existing literature had different classification methods (Kemp 1997;Mundial 1997). Based on the existing literature and the development of environmental regulation policy in China, this paper argues that environmental regulation policy is based on three main instruments: command and control, market regulation, and voluntary regulation. Different environmental regulation instruments have different regulatory effects. In the existing literature, most scholars recognized the effect of market-based regulatory measures and believed that they can effectively reduce potential costs (Arimura 2002;Stavins 1998). Meanwhile, scholars suggested that government intervention can play a significant role in promoting environmental improvement (Kolstad 1996). It was more effective for local governments to formulate their own environmental regulation schemes than simply using emission limits (Williams 2012). In the study of China, the existing literature mainly affirmed the effectiveness of environmental regulatory policies of command and control and market regulation (Guo and Yuan 2020;Zhao et al. 2015). It was further found that the effects of various environmental regulatory policies are also heterogeneous for different industries (Li and Ramanathan 2018;Shen et al. 2019).

Green technology innovation
Green technology innovation can be understood as innovation in green technology. It was first introduced by Braun and Wield (1994) as a general term for technologies, processes, or products that reduce environmental pollution, energy, and raw material consumption. Several studies in the literature on green technology innovation have discussed whether green technology innovation can improve environmental performance. Jacobs et al. (2010) found that green technology innovation improved environmental performance as it reduced energy and consumption in the production process, which in turn reduced costs and environmental regulations, leading to improved economic performance. Cainelli et al. (2020) used EU companies' data to empirically test the ability of green innovation to promote recycling and reduce waste and material use. Using Chinese firm-level data, Wang et al. (2021) concluded that green process innovation and green product innovation can improve firms' economic performance through improved environmental performance. There were also studies discussing the impact of green technology innovation on financial performance (Aastvedt et al. 2021), green total factor productivity (Wu et al. 2022), and firms' competitive advantage (Tu and Wu 2021), among others.
Regarding the factors influencing green technology innovation, the existing literature focused on the impact of environmental regulation on green technology innovation. This part will be discussed in the next section. Existing studies also discussed the construction of telecommunication infrastructure (Tang et al. 2021), corporate social responsibility (Mbanyele et al. 2022;Yuan and Cao 2022), government subsidies , and manufacturing intelligence (Yang et al. 2022) on green technology innovation.

The impact of environmental policy regulation on green technology innovation
Regarding the relationship between environmental policy regulation and green technology innovation, Porter and Van der Linde (1995) proposed the Porter hypothesis, which suggested that appropriate environmental regulation could encourage firms to innovate and help them gain competitive advantage. This hypothesis further evolved into the Weak Porter Hypothesis, the Narrow Porter Hypothesis, and the Strong Porter Hypothesis. The Weak Porter Hypothesis suggested that environmental regulation could stimulate certain types of environmental innovation. The Narrow Porter Hypothesis suggested that flexible environmental policy instruments such as pollution charges or tradable permits provided greater incentive for environmental innovation among firms than prescriptive regulations such as technical standards. The Strong Porter Hypothesis suggested that welldesigned regulation could lead to innovation and compensate for the costs of compliance (Jaffe and Palmer 1997). Jaffe et al. (2005) argued that environmental policy interventions could create incentives that affect the development of new technologies and the speed and depth of their diffusion. Proponents of this view argued that appropriate environmental regulation could encourage firms to engage in green technological innovation (Chakraborty and Chatterjee 2017;Hille and Möbius 2018). Conversely, Sinn (2008) examined public policies to address greenhouse gas emissions from a supply-side perspective, proposing the "green paradox" view, whereby the implementation of environmental public policies led to accelerated energy extraction; accelerating greenhouse gas emissions and environmental regulation did not induce firms to innovate to meet environmental constraints. Stoever and Weche (2017) also argued that the compliance costs associated with environmental regulations had a crowding-out effect on firms' R&D investments and discourage green innovation. Studies also concluded that there was a non-linear relationship between environmental policy regulation and green technology innovation (Liu et al. 2020;Yuan et al. 2017). Kemp et al. (2000) argued that environmental regulation should not be limited to facilitating or inhibiting technological innovation, but should also consider the influence of other factors such as the network of firm relationships and the size of the industry concerned. According to Rexhäuser and Rammer (2013), environmental regulation on competitiveness can cause a heterogeneous impact depending on the type of environmental innovation.

The Pilot Zones for Green Finance Reform and Innovations and green technology innovations
A green finance policy is an environmental regulation based on market-based regulatory instruments. Existing studies have examined the effectiveness of the implementation of relevant green finance policies, particularly the effects of green credit policies. Liu et al. (2017) and Wang et al. (2020) found that green credit policies had significant financing penalties and disincentive effects on investment, suggesting that green credit policies effectively discouraged investment in energyintensive sectors. Using an optimal control model, Kang et al. (2020) argued that green credit policies could enable manufacturers to reduce supplier pollution to the desired level to create additional value-added. Sun et al. (2019) and Chen et al. (2022) regarded the Green Credit Guidelines as a quasi-natural experiment. They argued that green credit policies can impose long-term credit constraints on polluting firms and guide them toward green technological innovation to prevent pollution at the source. Compared with the abovementioned green credit policies, the policy of Pilot Zones for Green Finance Reform and Innovations is richer in environmental regulation means and gives local governments greater autonomy. The pilot policy is a combination of various kinds of policy instruments, based on the actual situation in each region with its focused pilot program. Zhu and Tan (2022) and Zhang and Li (2022) all concluded that comprehensive green finance policies can promote the development of green technology innovation. The Pilot Zones for Green Finance Reform and Innovations do not impose strict and uniform environmental standards at the national level; it delegates that authority to the pilot regional governments by imposing weak constraints. Compared to strong constraint policies, the pilot policy gives each pilot region's government more freedom to infuse regional characteristics in the implementation of green finance policies. Therefore, under the customized plan of local governments, the weak constraint policies implemented for the region can encourage corporates to implement green projects and subsidize corporates' green technology innovation behaviors, so as to bring about the development of regional green technology innovation more effectively.

Hypothesis 1 (H1):
The implementation of the Pilot Zones for Green Finance Reform and Innovations effectively promotes the development of green technology innovation of regional corporates.

Social finance and green technology innovations
Technology innovation activities are often subjected to severe external financing constraints due to high information asymmetry and uncertainty of returns, which can have a disincentive effect on technology innovation (Guariglia and Liu 2014). From a market perspective, green technology innovation has a lower rate of return on investment, longer time horizon, and higher investment risks than traditional technology innovation, exposing it to financing constraints and requiring more social funding to break through the path dependence of traditional technology innovation. Under this circumstance, it is important for local governments to support corporates engaged in green technology innovation. The implementation of national and industrial policies can significantly impact firms' financial activities ). Local governments often use credit interventions to support specific industries in response to policy calls. The policy of Pilot Zones for Green Finance Reform and Innovations proposes to guide the financial system to support the development of green industries, encourage the development of green credit, broaden green financing channels, and guide the flow of funds into green projects. Under the guidance of policies, local governments can reduce the information asymmetry of green enterprises through public opinion guidance and government endorsement and guide social funds to flow into green enterprises. Therefore, with the positive response of local governments to the policy, the pilot policy can alleviate the information asymmetry of green enterprises, guide the flow of social funds into green projects, alleviate the financing constraints of green enterprises, and promote the innovation and development of green technology innovation of regional enterprises.
Hypothesis 2 (H2):The implementation of the Pilot Zones for Green Finance Reform and Innovations has a positive impact on the green technology innovation of regional corporates by improving social financing.

Talent support and green technology innovations
China proposes a talent-driven innovation strategy. The support and cultivation of talent help to transform and apply original innovative knowledge, which in turn promotes technology innovation in enterprises. The greater the density of talent in a region, the stronger the talent market, and, therefore, the more technology innovation talent firms can bring in to drive their technology innovation activities (Rosen 1983). Local governments play a crucial role in talent introduction and retention. Under the guidance of green finance policies, local governments will strengthen the absorption and cultivation of green talents. The Pilot Zones for Green Finance Reform and Innovation policy proposes to strengthen the policy of supporting talent by vigorously promoting green development talents to achieve a sustainable green development pattern. On the one hand, this pilot policy can incentivize local governments to expand the financing channels of green enterprises in the pilot areas and promotes their green technological innovation activities by introducing high-level financial talents and creating innovations in green financial products and services. On the other hand, in the process of implementing the pilot policy, local governments will provide talent subsidies for higher education institutions to encourage them to train green talents, strengthen the pool of green technology innovation talents, and create incentives for enterprises in the pilot areas to introduce green technology innovation talents, inducing them to engage in green technology innovation activities. It is particularly difficult for heavy polluting manufacturing enterprises to achieve a green transformation of technological innovation in a short period due to the path dependence of their innovation activities. Therefore, the introduction of green technology innovation talent can help increase enterprises' original green technology innovation knowledge reserve to enable them to effectively carry out the transformation and application of green technology innovation knowledge to achieve green transformation of technology innovation.

Hypothesis 3 (H3):
The implementation of the Pilot Zones for Green Finance Reform and Innovations has a positive effect on the green technology innovation of regional corporates by encouraging the introduction and reserve of green talents.

Government financial support and green technology innovations
China's intensified implementation of a national innovationdriven development strategy has led to an increase in technology innovation prioritized by the government. As the government's main source of funding to support enterprise science and technology innovation, fiscal spending on science and technology has a very important impact on China's enterprise technology innovation and the transformation and upgrading of the industrial structure. Under the guidance of green finance policies, local governments can strengthen the optimal allocation of green financial resources on the supply side, which plays an important role in alleviating the financing constraints of green enterprises. The alleviation of financing constraints can encourage green enterprises to implement green projects and promote green development with green technology innovation. The policy of Pilot Zones for Green Finance Reform and Innovations mentions the need to strengthen local financial support and increase financial investment in the pilot zones to prompt industries to complete green transformation and upgrading. Enterprises may experience difficulty in obtaining social financing for green technology innovation projects due to the long payback period and low return on investment. Thus, on the one hand, the increase in fiscal spending helps enterprises implement green technology innovation projects to access government funding. On the other hand, government support for such enterprises will have a "demonstration effect" and facilitate access to social finance to promote green technology innovation activities.

Hypothesis 4 (H4):
The implementation of the Pilot Zones for Green Finance Reform and Innovations has a positive effect on the green technology innovation of regional corporates by strengthening the financial support of local governments for green enterprises.

Model setting
This paper examines the policy effects of Pilot Zones for Green Finance Reform and Innovations using the green technology innovation activities of listed manufacturing enterprises as a research lens. In the literature assessing policy effects, the difference-in-difference (DID) model is an effective method. This paper's DID model is constructed as follows: GTI is the explained variable, which represents green technology innovations. The subscripts i and t represent the corporate and the year, respectively. The explanatory variable is DID, which is a 0-1 dummy variable. X is a set of control variables, including corporate profitability, corporate growth, firm size, and capital intensity. λ is the time-fixed effects, μ is the individual-fixed effects, and ε is the stochastic disturbance term. In the above model, β measures the net effect of the Pilot Zones for Green Finance Reform and Innovations on corporate green technology innovations.

Explained variable
This paper uses the overall number of independent green patent applications by listed companies (GTI) as the explained variable. Patent data is a better visual indicator of the output of technology innovation activities than R&D. Moreover, patent data can be further segmented and used to examine the differences in the impact of this pilot policy on different (1) GTI it = α + βDID it + γX it + λ t + μ i + ε it types of patents. This paper distinguishes between independent green invention patent applications (GTI_INV) and independent green utility model patent applications (GTI_UTI) based on the technical nature of the patents for patent heterogeneity analysis.

Explanatory variable
The DID in our DID model is the interaction term between pilot and post (pilot × post). The pilot region (pilot) in our DID model is a 0-1 dummy variable, which takes the value of 1 if the enterprise's registered location belongs to a pilot region in the Pilot Zones for Green Finance Reform and Innovations, and 0 if otherwise. The pilot time (post) is also a dummy variable that takes the value of 1 if the current year is the year in which the pilot policy is proposed (2017 to 2019), and 0 if it is before the proposal (2014 to 2016). This paper focuses on the DID (β) coefficient. This coefficient reflects the impact of the pilot policy on the green technology innovation of enterprises in the pilot region. If the coefficient is significantly positive, it indicates that the Pilot Zones for Green Finance Reform and Innovations have promoted green technology innovation activities of enterprises in the pilot regions.

Control variable
The control variables used in this paper are corporate profitability (Roe), corporate growth (growth), firm size (size), and capital intensity (Capint). Corporate profitability is measured by returns on equity. Return on equity is a measure of long-term profitability. Companies with high return on equity tend to be more innovative and have a higher level of participation in green technology innovation activities. Corporate growth is measured using the growth rate of revenue to determine a company's ability to grow. Companies with better growth tend to be more innovative, thus influencing their technology innovation activities. Firm size is measured using the total assets of the firm at the end of the year. Larger companies will focus more on R&D investment to maintain a stable level of technological development. More capital-intensive companies will spend more time selecting and training staff to improve labor productivity and are more likely to bring in technological innovators to influence their innovation activities. Table 1 shows the variable definitions and descriptive statistics.

Data source
As green technology innovation is mainly concentrated in the manufacturing industry, this paper uses a selection of Chinese A-share listed manufacturing enterprises as the research sample. It focuses on 3 years before and after the establishment of the Pilot Zones for Green Financial Reform and Innovations (2014 to 2019) as the time window to mitigate other exogenous events and uses a DID model to examine the policy effects of this pilot policy. The sample companies are filtered in this paper as follows: (1) excluding the sample of enterprises listed after 2014; (2) excluding the sample of enterprises with abnormal financial conditions during the sample observation period (ST, *ST, and PT enterprises); and (3) excluding the sample of enterprises with significant missing variable values. Ultimately, this paper obtains a total of 3714 sample observations from 619 listed manufacturing companies. To eliminate the influence of extreme values, the main continuous variables are trimmed at the 1% level. The data for the green patent was obtained from the CNRDS database; other variables were mainly obtained from the CSMAR database.

Parallel trend test
To ensure that the estimators are unbiased, a parallel trend test is performed on the green patent applications in the experimental and control groups as shown in Fig. 1. Before the pilot policy was proposed, the green patent applications in the experimental and control groups maintained a relatively consistent trend. After the introduction of the policy, there was a significant change in the overall trend of the green patent applications in the experimental and control groups. It is noteworthy that the green patent applications of both the experimental and control group companies declined significantly in 2019 due to the patent regulatory transformation carried out in China to improve the quality and optimize the structure of patent applications. Therefore, based on the results of the parallel trend test, a DID model can be used to test whether the Pilot Zones for Green Financial Reform and Innovations promote green technology innovation in manufacturing enterprises.

Basic regression analysis
Based on Formula (1), this paper uses green patent applications, green invention patent applications, and green utility model patent applications as the explained variables. The results are shown in Table 2. The implementation of the pilot policy significantly increased corporate green technology innovations; this result holds even after controlling for corporate profitability, corporate growth, firm size, capital intensity, time-fixed effects, and individual-fixed effects. Hypothesis 1 (H1) is validated. Regarding the effects, the pilot policy has been more effective in promoting green invention patent applications than green utility model patent applications. It has been more helpful in promoting substantive green technology innovations. Most traditional manufacturing enterprises are resource-consuming and environment polluting enterprises; thus, their green transformation requires more technological innovations to achieve green development. The Pilot Zones for Green Financial Reform and Innovations give local governments greater autonomy and provide a platform for the green transformation and upgrading of manufacturing enterprises and motivate enterprises to implement disruptive innovation research activities.

Dynamic effect analysis
With the gradual implementation of the Pilot Zones for Green Financial Reform and Innovations, the impact of the pilot policy on green technology innovation will also change. Therefore, this paper considers the existence of dynamic effects on the impact of the pilot policy on enterprises' green technology innovations. It constructs interaction terms between the pilot region dummy variable and the dummy variables for each year after the implementation of the pilot policy (2017 to 2019) to test for dynamic effects. The dynamic effect results are shown in Table 3. As captured in Table 3, the pilot policy has a significant and lasting contribution to green technology innovations. The Pilot Zones for Green Financial Reform and Innovations are established to explore replicable and scalable patterns and experiences, and it is primarily focused on how to achieve sustainable development. Therefore, the pilot policy has a long-term and far-reaching impact on green technology innovation.

Placebo test
To exclude the inherent differences between the experimental and control groups before the establishment of the pilot policy, this paper draws on the study of Bakke et al. (2016) to advance the establishment of the pilot policy to 2015. It examines whether there is an impact of this virtual policy on corporates' green technology innovations. If the findings of this paper were due to inherent differences between the experimental and control groups, the same conclusions could be drawn using this virtual policy. The results are shown in column (1) of Table 4, where the coefficient of the interaction term DID is not significant, indicating that the inherent differences between corporates in the experimental and control groups before the implementation of the pilot policy are similar to the findings of this paper.

PSM-DID
The corporates in both the experimental and control groups selected for this paper cover different industries; thus, there may be differences in corporate characteristics between the two groups. This paper matches the control group using the propensity score matching (PSM) method with matching variables of corporate profitability (Roe), corporate growth (growth), firm size (size), and capital intensity (Capint) with a caliper set at 0.01. The matching effect of the PSM method is shown in Fig. 2, from which it can be seen that the %bias of all covariates is significantly smaller than before matching.
The DID model is re-estimated using the matched control group sample, and the results are presented in column (2) of Table 4. The regression result shows that the coefficient of the interaction term DID is significantly positive, which is consistent with the result in Table 2. Thus, this paper further excludes the interference in the conclusions caused by the differences in firm characteristics between the experimental and control group of firms. It also proves the robustness of the empirical results of this paper.

Add control variables
To alleviate the problem of missing explanatory variables, a series of control variables have been added to enhance the robustness of the empirical results. The added control variables include two jobs in one (duality); if the chairman and general manager are concurrently held by the same person, the value is taken as 1, otherwise it is 0. Board structure (Indrate) uses the ratio of the number of independent directors to the total number of directors. Executive compensation incentives (incentive) are calculated using the logarithmic of the total compensation of the top 3 executives. Equity concentration (Cr) uses the shareholding ratio of the largest shareholder. Environmental investment (GInvest) is calculated using the logarithmic of the amount of environmental investment of the corporate. After adding the above control variables, the result is shown in column (3) of Table 4. The result is basically consistent with Table 2, which indicates that after alleviating the problem of missing explanatory variables, the implementation of the pilot policy can significantly promote the development of green technology innovation of regional enterprises. The conclusion of this paper is robust.

Heterogeneity of industry pollution levels
Following the Chinese Ministry of Environmental Protection's Guidelines on Environmental Information Disclosure for Listed Companies, this paper selects eight manufacturing industries: textile, tannery, building materials, paper, petrochemical, pharmaceutical, chemical, and metallurgy, as heavily polluting industries. The sample is divided into heavily polluting and non-heavily polluting industries. The paper examines whether there is heterogeneity in the impact of the implementation of the pilot policy on green technology innovation among enterprises with different levels of industrial pollution. The regression results in Table 5 show that the coefficient of the interaction term DID in heavily polluting industries is negative but not significant, while the coefficient in non-heavily polluting industries is positive and significant at the 1% level of significance. It suggests that the implementation of the pilot policy has a significant effect in promoting green technology innovation in non-heavily polluting enterprises in the short term, but not in heavily polluting industries. There are several possible reasons for this result: First, compared to non-heavily polluting industries, enterprises in heavily polluting industries tend to require a longer period of green transformation of technology innovation to achieve green development, making it more difficult for these enterprises to complete the adjustment of greening their technology innovation activities in the short term after the implementation of the pilot policy. Second, the Pilot Zones for Green Financial Reform and Innovations propose the restriction or withdrawal of highly polluting projects and impose a "one-vote veto" on environmental protection in terms of financing. This pilot policy gives local governments greater power to promote the development of green projects, so local governments will impose strong restrictions on heavy polluting enterprises under the promotion of the policy. This has resulted in financial constraint for some corporates in heavy polluting industries such that they may not have the cash flow to engage in green technology innovation activities in the short term.

Heterogeneity of high-tech enterprise certification
This paper divides the sample enterprises into high-tech and non-high-tech enterprise groups based on whether they have obtained high-tech enterprise certification during the observation period. It further examines whether there is heterogeneity in the impact of the establishment of the pilot policy on green technology innovation by high-tech enterprise certification. In Table 6, the coefficient of the interaction term DID for high-tech enterprises is positive and significant at the 1% significance level, while the coefficient for non-hightech enterprises is not significant. This indicates that the implementation of the pilot policy has a more significant impact on the green innovation activities of high-tech certified enterprises than non-high-tech certified enterprises. As knowledge-intensive and technology-intensive enterprises, high-tech enterprises have a systematic technology innovation model and a wealth of technology innovation elements and are more aware and capable of green technology innovation. Such enterprises will be favored by local governments, and local governments will also give corresponding policy preferences to high-tech enterprises. Therefore, the financial and tax incentives for high-tech qualified enterprises will further reduce the cost of innovation for high-tech enterprises, providing an incentive for enterprises to engage in green technology innovation activities and thus promote green technology innovation.

Heterogeneity of firm size
Following the classification criteria of the National Bureau of Statistics of China for enterprise size, this paper divides the sample enterprises into large enterprises and SMEs to explore whether there is heterogeneity of firm size in the impact of the establishment of the pilot policy on enterprise green technology innovations.
In Table 7, the coefficient of the interaction term DID for large enterprises is positive and significant at the 1% significance level, while the coefficient for SMEs is not significant, which indicates that the implementation of the pilot policy has a stronger effect on promoting green technology innovations in large enterprises than in SMEs. The financial and scale advantages of large enterprises make them more capable of participating in green technology innovation activities than SMEs. At the same time, local governments have certain government-enterprise ties with large local enterprises, and local governments are more willing to cooperate with large enterprises to promote green projects. In this case, large enterprises are also more willing to participate in green technology innovation activities to expand their corporate reputation. For SMEs, the greater pressure on financing and the uncertainty of future returns are major disincentives to engage in green technology innovation activities.

Mediation test
This paper further analyzes the mediating effects of social financing, talent support, and government financial support respectively. It uses the increment of social financing, the number of undergraduate graduates, and the amount of local fiscal expenditure on science and technology as mediating variables for testing as shown in Table 8. As the coefficients of the three mediating variables are not significant in the third step of the mediation test when they are introduced into the model, this paper further examined them using the Bootstrap test concerning the study by Wen and Ye (2014). The Bootstrap test results are shown in Table 9. Table 9 shows that the confidence intervals for indirect effects do not contain 0, which proves that social financing, talent support, and government financial support all have mediating effects. Hypotheses 2, 3, and 4 are verified. This suggests that the Pilot Zones for Green Financial Reform and Innovations can promote corporate green technology innovation activities by encouraging social financing, strengthening talent support, and providing government financial support. The pilot policy stimulates social financing to actively favor green projects in the pilot regions; provides financial support for the research, development, and application of green technologies in enterprises; and alleviates enterprises' financial constraints resulting from green technology innovation, thus promoting green technology innovation in the pilot regions. Meanwhile, the governments of the pilot regions are actively implementing policies to support and incentivize the green technology innovation talent pool to promote the transformation and application of original green technology innovation elements, thereby enhancing the exchange of green technology innovation among enterprises in the region and promoting the green transformation of technology innovations. Additionally, to promote green development, the government has increased financial expenditure on science and technology to encourage enterprises to participate in green technology innovation projects, while projects carried out under government endorsement can further attract more social investment to green projects, thus promoting the development of green technology innovation and industrial green transformation of enterprises.

Conclusions
China's long-established but sloppy industrial pattern of development has trapped the country in an "environmental-economic loop," where resource and environmental issues have become limits to China's sustainable development and have Using a DID model, this paper conducts a parallel trend test and finds that the establishment of the pilot policy can promote green technology innovation activities of manufacturing enterprises in the pilot regions. This conclusion remains valid after robustness tests. Meanwhile, heterogeneity is established in the impact of the establishment of the pilot policy on corporate green technology innovation. As it is more difficult for enterprises in heavily-polluting industries to achieve a green transformation in technology innovation, the pilot policy is therefore crucial for promoting green technological innovation among enterprises in non-heavily polluting industries, but not for enterprises in heavily polluting industries. Compared to non-high-tech certified enterprises, high-tech certified enterprises have a more systematic innovation pattern and enjoy financial and tax benefits; thus, the pilot policy has a significant effect on promoting green technology innovation for high-tech certified enterprises, but not for non-high-tech certified enterprises. Large enterprises are more inclined to participate in green technology innovation activities than SMEs because of their capital and scale advantages and their desire to expand their reputation.

Policy implications
China should fully develop green finance to guide manufacturing enterprises to green transformation and upgrading. Although China's exploration of green finance is beginning to bear fruit, some financial institutions still have concerns about the risks of green projects. The implementation of the Pilot Zones for Green Financial Reform and Innovations can effectively promote enterprises' green technology innovation activities, which is a useful innovative green financial reform practice at the grassroots level as it promotes the green development of enterprises. The government should therefore further improve policies that support green finance to ensure their combined implementation and explore a more comprehensive green finance policy mechanism to incentivize financial institutions to participate in green projects and guide the flow of financial resources into the green sector. Furthermore, China should establish an effective transmission mechanism to encourage manufacturing SMEs and non-high-tech certified enterprises to actively participate in green technology innovation activities to ensure that green finance truly serves the green development of the real economy. Furthermore, China should accelerate the green technology transformation of enterprises in heavily polluting industries.
The implementation of the Pilot Zones for Green Financial Reform and Innovations does not significantly impact the promotion of green technology innovation in heavily polluting enterprises. This may be due to the short policy implementation cycle and the fact that it is more difficult for enterprises in heavily-polluting industries to fully implement adjustments to their green technology innovation activities. Green technology innovation plays an important supporting role in promoting pollution prevention and control as an important path for enterprises to accomplish carbon emission reduction targets and achieve sustainable economic development. Innovative breakthroughs in green technology will strengthen the accessibility and economic viability of pollution control technologies and harmonize the relationship between ecological protection and economic development. Therefore, it is pertinent that the government further develops corresponding policies for heavily polluting industries and restricts heavily polluting projects. It should also implement subsidies and other supportive policies for heavily polluting enterprises participating in green technology innovation activities to help enterprises in heavily polluting industries accelerate the process of green technology transformation and promote the construction and development of a green manufacturing system.
Author contribution Xinyu Sun contributed to the analysis and manuscript preparation: performed the data analysis and wrote the manuscript. Aili Zhang contributed to the conception and supervision of the study. Mengze Zhu contributed to the data collection and supervision of the study. All authors have read and agreed to the published version of the manuscript.
Funding This research was funded by the National Social Science Foundation Major Project (No. 17ZDA119) and National Science and Technology Statistics Special Work (No. NSTS202109).
Data availability Data will be made available on request.

Declarations
Ethics approval Not applicable.

Competing interests
The authors declare no competing interests.