Water-saving dry methanation for direct conversion of syngas to synthetic natural gas over robust Ni0.1Mg0.9Al2O4 catalyst

摘要

Production of synthetic natural gas (SNG) from coal is typically water intensive due to the need of increasing H-2/CO ratio from 1 to 3 via water gas shift reaction. Here we report a water-saving dry methanation reaction that allows direct conversion of low H-2 content syngas (H-2/CO = 1) to methane without consumption of water for adjusting H-2/CO to >= 3 and without production of waste water. Conventional Ni/Al2O3 catalyst is active for the dry methanation reaction but deactivates very rapidly due to carbon deposition and metal sintering. A Ni0.1Mg0.9Al2O4 catalyst exhibits much higher activity and better stability during steady state catalytic reaction and cyclic reaction-regeneration operations. Using a suite of characterization tools including BET, XRD, STEM, TEM, H-2-TPR, Raman, TG-DSC, CO2 and NH3 TPD, and temperature-programmed hydrogenation, we reveal that carbon deposition did not occur on the surface of Ni particles in Ni0.1Mg0.9Al2O4 catalyst. Moreover, the population of small Ni nanoparticles (ca. 2 nm) increased after multiple reaction-regeneration operations possibly due to Ni redispersing via reversible diffusing among the framework of spinel. The exposure of active Ni surface and the formation of small-sized Ni nanoparticles together contributed to the stable and improved activity for dry methanation during the reaction-regeneration operations. (C) 2019 Elsevier Inc. All rights reserved.