An attractive solution for improvement of pyrolysis bio-oil composition regarding the high content of oxygenated compounds is catalytic upgrading via hydrotreating process. The objective of this work is to evaluate the catalytic activity of CoMo /γ-Al2O3-HMS in bio-oil hydrotreating. The catalyst was characterized by surface area, X-ray diffraction (XRD), TEM, FT-IR and XPS analysis. The experiments were carried out in a flow fixed-bed reactor at the temperature range of 250-320 oC, pressure between 20-40 bar, and LHSV 3h-1. The results showed that increased temperature and pressure favors the hydrodeoxygenation process, reaching the maxim bio-oil conversion of 87.23%. Also, a chemical modelling algorithm was developed in order to evaluate the harmful emissions resulted from hydrotreating gaseous phase combustion. This calculation algorithm can be applied to any pressurized or atmospheric combustion engine fueled with different mixture of combustible gases such as: natural gas, hydrogen-enriched natural gas and oxy-fuel.