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

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 degrees 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 degrees C) and 1% Pt/H-MFI-90 (up to 40 degrees C) while 1%Pt/Al2O3 required a higher temperature of at least 320 degrees C. The average particle size obtained for Pt/SiO2 was 2-3 nm 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 (>130 mu mol acid sites per gram) as support. 1% Pt/SiO2 showed the highest selectivity towards deoxygenation at 50 degrees C, whereas for 1% Pt/H-MFI-90 temperatures of about 150 degrees 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 degrees C that comprises hydrogenation in the first step and acid catalyzed dehydration combined with hydrogenation in the second step. (C) 2014 Elsevier B.V. All rights reserved.