Low temperature glycerol steam reforming over a Rh-based catalyst combined with oxidative regeneration

Abstract

A Rh on alumina catalyst was tested for glycerol steam reforming at 673 K, 4.5 bar and molar water/glycerol feed ratio (WGFR) of 19. Even though a conversion of glycerol into carbon-containing gaseous products of around 73% was observed at the beginning of the reaction, a progressive deactivation was noticed afterwards, less than 40% of glycerol being converted into carbon-containing gas products after 4 h of time-on-stream. On the other hand, the total glycerol conversion remained above 99% during the same period, thus indicating the increasing formation of coke and/or liquid products over time. The total glycerol conversion started to decrease more pronouncedly only after 6 h, reaching a value of approximately 92% after 13 h. SEM/EDS analysis of the used catalyst showed the presence of carbon deposits, Raman spectroscopy evidencing the dominant presence of amorphous carbon structures. Therefore, oxidative regeneration with air at 773 K was carried out. This temperature proved to be enough to gasify all removable coke (according to temperature-programmed oxidation results). After regeneration, almost complete recovery of catalytic performance was observed. In fact, maximum H-2 yields between 2.1 and 2.6 mol.mol(fed glycerol)(-1) were observed for the reaction cycles performed with intermediate oxidative regenerations. By combining glycerol steam reforming with periodic oxidative regeneration of the catalyst, superior average performance, compared to the case where no oxidative regeneration was used, was attained.