Effects of support and co-fed elements on steam reforming of palm fatty acid distillate (PFAD) over Rh-based catalysts

Abstract

The steam reformings of palm fatty acid distillate (PFAD) over Rh on MgO–Al 2O 3, Al 2O 3, and Ce–ZrO 2 (with Ce/Zr ratios of 3/1, 1/1, and 1/3) supports were studied. At 1023 K, the conversions of PFAD are almost 100%, while H 2, CO, CO 2, and CH 4 are the major products from the reaction with some amount of high hydrocarbon compounds i.e. C 2H 4, C 2H 6, and C 3H 6 also detectable. Among all catalysts, the highest H 2 yield with the greatest resistance toward carbon deposition and lowest formation of hydrocarbons in the product was achieved from Rh/MgO–Al 2O 3. The activities of all catalysts increased with increasing temperature; interestingly at temperatures above 1173 K, H 2 yields from the steam reforming over Rh/Ce–ZrO 2 (with Ce/Zr ratio of 3/1) become greater than those observed over Rh/Al 2O 3 and Rh/MgO–Al 2O 3. This great improvement is due to gas–solid reactions between hydrocarbons present in the system with lattice oxygen ( O O x ) at Ce–ZrO 2 surfaces simultaneously with the reaction taking place on the active sites of Rh. Rh/Ce–ZrO 2 with Ce/Zr ratios of 3/1 was then selected for further study by adding O 2 and H 2 along with PFAD and steam at the feed. An addition of both components significantly reduced the degree of carbon deposition and promoted the conversion of hydrocarbons to CO and H 2. Nevertheless, the presence of too much O 2 could oxidize Rh particles and combust H 2 to H 2O, which results in low reforming reactivity. Addition of too much H 2 also reduced the catalyst activity due to the active site competition with Rh particles and the inhibition of gas–solid redox reactions between the gaseous hydrocarbon components with lattice oxygen ( O O x ) on the surface of Ce–ZrO 2 support.