Fuel, Vol.220, 32-46, 2018
Effect of Mg-modified mesoporous Ni/Attapulgite catalysts on catalytic performance and resistance to carbon deposition for ethanol steam reforming
A series of Mg-modified mesostructured Ni/Attapulgite (Ni/xMg-ATP, x = 0, 5, 10, and 20 wt%) have been produced by a co-precipitation method. The textural and physicochemical properties of as-prepared precursors and derived catalysts were characterized by N-2 physical adsorption analysis, low-and wide-angle XRD, ICP-OES, H-2 pulse chemisorption, SEM/EDX-mapping, TEM, FT-IR, H-2-TPR and NH3-TPD. From N-2 physical adsorption analysis, all synthesized catalysts possessed unique mesostructure, resulting in the high metal dispersion and interaction between active metal and support as proven by XRD, FT-IR, SEM/EDX-mapping, TEM, and H-2-TPR. These properties became more distinct for Ni/10Mg-ATP sample, which had highest active metal surface area (0.69 m(2)/g(cat)) related to the smallest Ni crystal size (9.5 +/- 0.1 nm), the most uniform nickel particle size and the highly dispersed Ni metal (20.2%), accompanying with highest nickel-ATP interaction. These excellent properties made it show the highest ethanol conversion (100%) and H-2 yield (96.7%) and the longest stability (50 h), during ethanol steam reforming (ESR) under the T = 973 K, S/C = 1.5, and GHSV = 19,200-19,400 h(-1). Meanwhile increasing temperature was positive effect for ethanol conversion and inhibiting the selectivity to hydrocarbon (such as CH4 and C2H4). In addition, the product selectivity was also considered to investigate the influence of Mg on catalytic performance. Obviously, the C2H4 selectivity (< 1%), which was generally accepted as the precursor of coke deposition, was significantly decreased with the addition of Mg. It was related to the decrease of acidic strength on the catalyst surface, which resulted from the Mg introduction and was detected by NH3-TPD analysis. The spent catalysts after 50 h of ESR reaction were also investigated by XRD, SEM-EDX, TEM, and TG-DTG, the results suggested that the addition of Mg significantly suppressed the formation of filamentous carbon and the sintering of nickel particles, and further reduced the carbon deposition rate reduced to 6.1 mg.(g(cat) h)(-1) over Ni/10Mg-ATP.