Hydrogen production via Steam reforming of Glycerol over Rh-Al2O3 catalysts modified with CeO2, MgO or La2O3

Although the biodiesel industry has grown at a phenomenal 23% per annum during the past decade, its sustainable use is threatened by the production of increasing amounts of the main by-product of the transesterification reaction, i.e., unrefined glycerol (10 wt.% of the oil undergoing the reaction). However, glycerol could also be used for the production of hydrogen via the steam reforming reaction, which is strongly endothermic and is favoured at atmospheric pressure and high water to glycerol feed ratios. Nevertheless, the reaction network followed during the decomposition of glycerol is quite complex as it involves a number of parallel and consecutive steps of reaction intermediates such as dehydrogenation, dehydration, polymerization and isomerization. Moreover, the catalyst that will be used should promote the cleavage of C-C, O-H, and C-H bonds in the glycerol mole, while the cleavage of the C-O bonds needs to be avoided as it leads to the production of alkanes, which in turn lead to carbon deposition. Additionally, the catalyst should also allow the Water Gas Shift reaction to take place, so that absorbed CO from the surface can be removed as CO2. Thus, the main challenge that needs to be addressed is the development of highly active and stable catalysts that will be resistant to carbon deposition and metal particle sintering. The work presented herein compares the performance of an unmodified Rh-Al2O3 catalyst with Rh catalysts where alumina was modified with the addition of 10 wt.% of either CeO2 or MgO or La2O3. The catalysts were tested in terms of activity and stability, while the liquid products of the reaction were quantified. All samples were found selective towards H2, while time-on-stream experiments showed a very stable performance under harsh experimental conditions.