Syngas production using CO2-rich residues: From ideal to real operating conditions

Abstract

Employing a series of Cu-MnOx supported catalysts, this work investigates for the first time the impact on the RWGS reaction rate obtained under simulated residual CO2-rich feed streams, i.e., when CO and CH4 species are added to the reaction atmosphere. For this purpose, a simulated gaseous stream was prepared based on real biomass processing results. First, the series of catalysts was assessed under diluted ideal conditions (i.e., a mixture of only CO2 and H2 with N2 as dilutant). Here, the catalysts’ performance depended on both metal size and surface basic sites. Still, as the CO2 partial pressure was increased (varying the H2:CO2 ratio), the Cu metal dispersion seemed the catalyst feature governing RWGS reaction rate. Values of CO2 conversion from 50 to 60 % were registered for the different catalysts at a ratio H2:CO2 of 4. Then, under simulated residuals conditions and aside of thermodynamic limitations, the achievement of improved catalyst performances also depended on the catalysts’ reactivity towards the oxidation of CH4 fractions. For (X wt.%) Cu - (10 wt.%) MnOx/Al2O3 catalysts, 10 wt.% Cu was determined as the optimal Cu content. With this selected value, over the different analyzed supports (γ-Al2O3, (5 wt.%) SiO2-Al2O3, (40 wt.%) SiO2-Al2O3 and (20 wt.%) CeO2-Al2O3), the highest conversion rates with values of CO2 conversion of ca. 50 % at the higher temperature and optimal catalyst stabilities attained by the ceria supported catalyst (close to 95 % at most of the reaction temperatures) were ascribed to the optimal particle sizes and promoted CH4 activation processes.