| 内容提要: |
Energy is an indispensable element in our everyday lives. Nowadays most of the energy we use comes from fossil fuels—a non-renewable and unclean energy source. Therefore, it is urgent for us to explore renewable and clean energy. Hydrogen has been regarded as an ideal fuel to support energy development because of its cleanness and high combustion efficiency. Among numerous approaches for producing hydrogen, steam reforming is a classical and efficient method. Recently, bioethanol steam reforming for hydrogen production has received increasing attention since bioethanol is renewable, cheap, easy to handle, low in toxicity, and thermodynamically feasible to decompose. Among supported base-metals, Ni-based catalysts are excellent candidates for ethanol steam reforming (ESR) because of the intrinsic activity of nickel in C-C and C-H bond cleavages. However, one of major problems of Ni-based catalysts is sintering of Ni particles and carbon deposition. Oxygen mobility (OM) of CeO2 based support can resist coke formation, and the oxygen vacancy of CeO2 can suppress nickel sintering, so CeO2-based support has been widely investigated for ESR. Doping Mg into CeO2 lattice can effectively enhance surface oxygen vacancy of CeO2, and so can better suppress carbon deposition.
This paper describes a strategy of increasing oxygen storage capacity (OSC) of ESR catalysts. We have prepared a series of Mg modified CeO2 by citric acid sol-gel method. Ni particles were loaded by impregnation method. The catalysts were characterized by N2 adsorption/desorption, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), O2 volumetric chemisorption and thermo gravimetric analysis (TGA). The insertion of Mg into the CeO2 lattice efficiently promotes the reduction of Ce4+ according to XRD and TPR analysis. Mg modified Ni/CeO2 catalysts have larger OSC and smaller nickel crystallite size compared to bare Ni/CeO2. The optimal Mg addition is 7 mol% (Ni/7MgCe) with the best OM. We also present evidence indicating that Mg addition significantly promotes ethanol conversion and H2 production in ESR, and that Ni/7MgCe yields the best performance due to the high OM of the support. These Mg modified catalysts also produce less carbon deposition compared to Ni/CeO2, and the amount of deposited carbon decreases with increasing Mg addition. Ni/7MgCe has the best resistance to carbon deposition owing to the excellent OM. |