Catalytic hydrodeoxygenation of guaiacol over platinum supported on metal oxides and zeolites

Abstract

Hydrodeoxygenation of guaiacol over Pt-based catalysts was studied as a representative for phenolic compounds in pyrolysis oil. Screening of various Pt-based catalysts supported on different oxides and using different preparation methods resulted in 1% Pt/SiO2 and platinum supported on zeolites, such as 1% Pt/H-MFI-90, as the most promising catalysts in a temperature range up to 200°C. Thereby conversions of 86 % and 100 % were received, respectively. Particularly, selectivities to cyclohexane above 90 % were achieved for 1% Pt/H-MFI-90.X-ray absorption near edge structure (XANES) uncovered that mild reduction temperatures were sufficient for the reduction of 1% Pt/SiO2 (up to 150°C) and 1% Pt/H-MFI-90 (up to 40°C) while 1%Pt/Al2O3 required a higher temperature of at least 320°C. The average particle size obtained for Pt/SiO2 was 2–3nm as unraveled by scanning transmission electron microscopy (STEM) and extended X-ray absorption fine structure (EXAFS). The deoxygenation ability of the catalysts was improved if the Pt particles were deposited on an acidic H-MFI zeolite (>130μmol acid sites per gram) as support. 1% Pt/SiO2 showed the highest selectivity towards deoxygenation at 50°C, whereas for 1% Pt/H-MFI-90 temperatures of about 150°C were required to achieve a high selectivity to cyclohexane. For the latter catalyst a longer reaction time was beneficial to maximize the selectivity towards cyclohexane. The hydrogen pressure did not have significant influence on the reaction rate. The results are in agreement with a hydrodeoxygenation mechanism over Pt/zeolite catalysts at temperatures up to 200°C that comprises hydrogenation in the first step and acid catalyzed dehydration combined with hydrogenation in the second step.