Microkinetic modelling of CO2 and methane conversion into syngas on a low metal-loaded Rh/Al2O3 catalyst: Effect of co-feeding reaction products

The effects of co-feeding the components of syngas (H2 or CO) in the CO2 and methane dry reforming were studied on a 0.5 wt% Rh/Al2O3 catalyst by microkinetic modelling. Different inlet compositions, reaction temperatures (700–750 °C) and space velocities (530–2100 NL/(gcat·h)) were tested to develop a model consisting of 86 elementary reaction steps. The model described satisfactorily the trends found for CO2 and CH4 conversions, H2 and CO yields, and selectivities. Dehydrogenation of CH2* was identified as the rate determining step. The reaction pathway was not altered by H2 or CO co-feeding. Increasing the H2 concentration in the feed resulted in positive effects on the reactants conversions and syngas yield, due to augmented partial surface coverage by OH* and O* species, thus causing promoting effects on the reverse water–gas shift and methane steam reforming reactions. Conversely, CO co-feeding had negative effects on CO2 conversion, and H2 and CO yields, due to the high partial coverage of CO* and C*, which negatively affected the CO2 conversion and CH2* dehydrogenation step. This study provides new insights into the joint conversion of CO2 and CH4 into syngas on a low-loading Rh catalyst, showing the benefits of co-feeding hydrogen.