Enhancing preferential oxidation of CO in H₂ on Au/α-Fe₂O₃ catalyst via combination with APTES/SBA-15 CO₂-sorbent

Au/α-Fe₂O₃ was combined with a CO ₂-sorbent (3-aminopropyltriethoxysilane (APTES) grafted on SBA-15 and hereafter denoted as APTES/SBA-15) to enhance preferential oxidation (PROX) of CO in H₂. The CO₂ molecules could be rapidly adsorbed on APTES/SBA-15 at low temperatures below 50 °C with a capacity of 0.68 mmol CO₂/g-sample, and desorbed at a temperature range of 50 °C-80 °C. Three different configurations of the Au/α-Fe₂O ₃ catalyst and the CO₂-sorbent were tested in the PROX reaction, namely (i) the sorbent-free (catalyst//SBA-15//catalyst) configuration, (ii) the packed three-layer configuration (catalyst//CO ₂-sorbent//catalyst), and (iii) the mechanically mixed catalyst and CO₂-sorbent configuration. Compared to configuration (i), configuration (ii) achieved an average 10% higher CO conversion at 50 °C and a GHSV of 65000 h^-1. However, the CO concentration could not be lowered to below 70 ppm from 2000 ppm using configuration (ii) at a GHSV of 10000 h^-1. Thus, a 5-layer configuration (catalyst//CO ₂-sorbent//catalyst//CO₂-sorbent//catalyst) was used, and the CO concentration was lowered to ca. 25 ppm. The mechanism for enhancement of the PROX reaction by the continuous removal of CO₂ by the CO ₂-sorbent is discussed and attributed to reduction of the surface carbonate on the Au/α-Fe₂O₃ catalyst formed during the PROX process.