Monometallic Carbonyl-Derived CeO2-Supported Rh and Co Bicomponent Catalysts for CO-Free, High-Yield H-2 Generation from Low-Temperature Ethanol Steam Reforming

摘要

CeO2-supported Rh and Co bicomponent catalysts derived from monometallic carbonyls and prepared from metal nitrates for low-temperature ethanol steam reforming (ESR) have been studied by catalytic testing using a multi-channel reactor, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), H-2 chemisorption, transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX), powder X-ray diffraction (PXRD) and IR spectroscopy. Reaction product analysis shows that low-temperature ESR proceeds mainly through 1) adsorbed oxametallacycle decarbonylation (OD) and acetaldehyde steam reforming (ASR) on Rh/CeO2, 2) ethanol dehydrogenation to acetaldehyde, ASR, and water-gas shift (WGS) on Co/CeO2, and 3) OD, ASR, and WGS on (Rh+Co)/CeO2. The addition of Co to Rh/CeO2 results in decreased catalytic selectivity towards CO and CH4. The carbonyl-derived (Rh+Co)/CeO2 displays marked advantage over the nitrate-prepared catalyst, leading to CO-free H-2 generation with H-2 yields as high as 4.3 mol(H2) mol(C2H5OH)(-1) at temperatures as low as 300 degrees C. Combined studies by TPR, XPS, H-2 chemisorption, and TEM-EDX suggest significant interaction between the Rh and Co atoms in carbonyl-derived (Rh+Co)/CeO2, in contrast to nitrate-prepared catalysts, which is assumed to promote efficient WGS during the ESR process. Catalyst deactivation, possibly as a result of catalyst sintering, metal oxidation, and coke deposition during ESR, is discussed in terms of TPR, XPS, TGA, TEM, and PXRD. A WGS-ESR bilayered catalyst system of Rh/CeO2(Rh+Co)/CeO2 is successfully applied to the CO-free and high-yield production of H-2 from low-temperature ESR.