A strategy to regenerate coked and sintered Ni/Al2O3 catalyst for methanation reaction

Supported Ni/Al₂O₃ catalysts are widely used in chemical industries. Regeneration of the deactivated Ni catalysts caused by sintering of Ni nanoparticles and carbon deposition after long-term operation is significant but still very challenging. In this work, a feasible strategy via solid-phase reaction between NiO and Al₂O₃ followed by a controlled reduction is developed which can burn out the deposited carbon and re-disperse the Ni nanoparticles well, thus regenerating the deactivated Ni catalysts. To demonstrate the feasibility of this method, Ni catalyst supported on α-Al₂O₃ (Ni/Al₂O₃) for CO methanation reaction was selected as a model system. The structure and composition of the fresh, deactivated and regenerated Ni/Al₂O₃ catalysts were comprehensively characterized by various techniques. The reduction and redistribution of Ni species as well as the interfacial interaction between Ni nanoparticles and Al₂O₃ support were investigated in detail. It is found that calcining the deactivated Ni/Al₂O₃ in air at high temperature can burn out the coke, while the sintered Ni species can combine with superficial Al₂O₃ to form a surface NiAl₂O₄ spinel phase through the solid-phase reaction. After the controlled reduction of the NiAl₂O₄ spinel, highly dispersed Ni nanoparticles on Al₂O₃ support are re-generated, thus achieving the regeneration of the deactivated Ni/Al₂O₃. Interestingly, compared with the fresh Ni/Al₂O₃ catalyst, the sizes of Ni nanoparticles became even smaller in the regenerated ones. The regenerated Ni/Al₂O₃ showed much enhanced catalytic activity in CO methanation and became more resistant to carbon deposition, due to the better dispersed Ni nanoparticles and strengthened interaction between Ni and Al₂O₃ support. Our work not only addresses the long existing catalyst regeneration issue, but also provides effective and renewable Ni-based catalysts for CO methanation.