Hydrodeoxygenation Of M-cresol Catalyzed By Pt Supported Over Beta Zeolites

The use of fossil fuels such as coal,oil and natural gas generate a lot of sulfur dioxide and soot emissions,causing serious pollution of acid rain and air pollution.With the understanding of human on the environmental pollution and resource crisis deepening,renewable,biodegradable and other properties of natural polymer,is paid increasing attention.Lignin is an important renewable carbon source and the use of lignin to produce bio-oil and high value-added chemicals have been widely studied.Fast pyrolysis of lignin yields oxygen-rich bio-oils,such as phenols,anisoles,guaiacols and syringols,which is instability,viscosity and corrosive.In order to upgrade bio-oils,hydrodeoxygenation(HDO)is needed to make these products as conventional fuels’ substitutes.Hydrodeoxygenation activity of phenolics over bifunctional catalyst is high,but the specific reaction route is not clear,the purpose of this work is to gain insights into the reaction pathway of hydrodeoxygenation of phenolics over a Pt/HBeta catalyst.Hydrodeoxygenation of m-cresol has been studied on a Pt/HBeta catalyst at 225-350 °C and ambient hydrogen pressure.At 250 °C,m-cresol conversion proceeds through two reaction pathways:(1)direct deoxygenation(DDO path)to toluene,and(2)hydrogenation of m-cresol to methylcyclohexanone and methylcyclohexanol on Pt,followed by fast dehydration on the Br?nsted acid sites to methylcyclohexene(HYD path),which is either hydrogenated to methylcyclohexane on Pt or ring contracted to dimethylcyclopentanes and ethylcyclopentane on the Br?nsted acid sites.As the dehydration of methylcyclohexanol is much faster than the initial hydrogenation of m-cresol,the initial hydrogenation is the rate-determining step of the HYD path.Increasing temperature to 350 °C leads to the DDO path becoming the dominant path to toluene,while the HYD path followed by fast equilibration to toluene less important.The apparent activation energy of the DDO path is 49.7 kJ/mol but becomes negative for the HYD path.Consequently,increasing temperature enhances the contribution from the DDO path but reduces that from the HYD path through inhibiting the initial hydrogenation of m-cresol.In order to explore the influence of support on the catalytic reaction,three different acidic Beta zeolite catalysts(Pt/HBeta(Si/Al=19),Pt/NaHBeta and Pt/HBeta(Si/Al=290))are adopted for a comparative study.The results show that under low acid quantity,hydrodeoxygenation activity of m-cresol is higher.On the three catalysts,selectivity of DDO path and HYD path is not changed.Decrease of strong acid sites lead to decrease of ring contraction reaction,at 250 °C,compared with dehydrogenation to toluene,methylcyclohexene tend to generate methylcyclohexane through hydrogenation thermodynamicly,so methylcyclohexane selectivity is high at catalysts with weak acid sites.The dominant reason for catalyst deactivation may due to carbon deposition on acid sites.