Effect of oxygen addition, reaction temperature and thermal treatments on syngas production from biogas combined reforming using Rh/alumina catalysts

Dry reforming and partial oxidation of biogas were studied using 0.5 wt.% Rh/Al2O3 catalysts, both inhouse prepared and commercial. The effects of O-2 addition on syngas yield and biogas conversion were studied at 700 degrees C using different O-2/CH4 ratios in the gas feeding stream: 0 (dry reforming), 0.12, 0.25, 0.45 and 0.50. The highest CH4 conversion, H-2 yield and H-2/CO molar ratio were obtained with an O-2/CH4 ratio of 0.45, even though simultaneous valorization of both CH4 and CO2 could be best attained when the O-2/CH4 ratio was 0.12. Increased biogas conversions and syngas yields were obtained by increasing reaction temperatures between 650 and 750 degrees C. A detrimental influence on catalytic activity could be observed when the catalyst was subjected to calcination. Increasing the hold time of the thermal conditioning of the catalyst under inert flow altered Rh dispersion, though had no significant impact on catalyst performance in the dry reforming of methane at 700 degrees C and 150 N L CH4/(g(cat) h). Characterization of spent samples after reaction by Raman spectroscopy revealed the presence of carbonaceous deposits of different nature, especially on the commercial (named as Rh corn) and calcined (Rh calc) catalysts, though oxygen addition in the biogas feed significantly reduced the amount of these deposits. The Rh catalysts that had not been calcined after impregnation (Rh prep) did not present any noticeable characteristic peaks in the G and D bands. In particular, scanning transmission electron microscopy (STEM) images of the spent Rh prep sample revealed the presence of very highly dispersed Rh nanoparticles after reaction, of particle sizes of about 1 nm, and no noticeable C deposits. Combined oxy-CO2 reforming of biogas using highly dispersed and low metal-loading RhAl2O3 catalysts with low O-2 dosage in the reactor feed can be used to effectively transform biogas into syngas. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.