Attrition-resistant Ni–Mg/Al2O3 catalyst for fluidized bed syngas methanation

Abstract

Spray granulation was applied to prepare attrition-resistant Ni–Mg/Al₂O₃ catalysts for fluidized bed methanation. The tested binders included alumina sol (AS, pH = 4.0), acidic silica sol (SS, pH = 3.0), alumina-modified silica sol (AM, pH = 8.7) and alkaline silica sol (CC, pH = 9.6). By air-jet attrition test it was found that the attrition strength of the resulting catalysts followed an order of C-SS > C-AM > C-AS > C-CC, here C-SS, as an example, refers to the catalyst using SS as the binder. Characterization shows that the higher the volume of pores above 20 nm, the less attrition resistance of the catalyst there was, especially for catalysts using silica binders, whose high particle density was also beneficial to improving the attrition resistance of the catalyst. Syngas methanation over the catalysts in a fluidized bed at 2.5 MPa clarified an activity order of C-AS > C-SS > C-AM ≈ C-CC at 623–923 K. The AS binder enabled highly dispersed metallic Ni and many surface active sites for methanation reactions. Continuous methanation for 20 h at 900 K and 2.5 MPa verified the stability of the catalysts using the AS, SS and CC binders, but the activity clearly decreased over C-AM. Analyzing the spent catalysts via TPO demonstrated that a high amount of inactive carbon on C-AM caused its deactivation in the 20 h test.