Promotional effects of defects on Ni/HAP catalyst for carbon resistance and durability during dry reforming of methane

Abstract

Excellent carbon resistance and stable operations are essential for the industrialization of catalytic dry reforming of methane (DRM). In this study, a series of Ni/HAP and Ni/HAP-D catalysts are used to investigate their DRM reaction performance, including activity, durability, and resistance to carbon deposition. Combined with H2-TPR and XPS results, Ni in the Ni/HAP prefers to replace the external Ca atoms in hydroxyapatite. The inherently “Ca-deficient” HAP-D support facilitates a more robust anchor positioning for the Ni metal, and a significant fraction of the Ni atoms will be embedded in the inner structure of hydroxyapatite in the form of Ni2+[I] and Ni2+[II]. The catalytic activity of the Ni/HAP-D series of catalysts for CH4 and CO2 is significantly higher than that of the Ni/HAP series of catalysts, demonstrating that the Ni morphology, the combined form between Ni and support plays a crucial role in the DRM reaction. The deactivation rate of the Ni0.5/HAP-D catalyst is only 0.008% h−1 and 0.007% h−1 for CH4 and CO2, respectively, in a 200-h durability test. In the spent Ni0.5/HAP catalyst after 118-h reaction, the presence of NiO crystalline phase is detected, indicating that partial Ni is oxidized by CO2 during the reaction, and amorphous carbon and graphitic carbon are also detected. In contrast, no NiO crystalline phase is detected in the spent Ni/HAP-D catalyst after 200-h reaction, and only trace amounts of graphitic carbon are observed, indicating that the Ni presence pattern of Ni0.5/HAP-D contributes to its stability and resistance to carbon deposition. This work provides insights into the design of supported nickel-based catalysts with both excellent stability and surprisingly resistant to carbon deposits for DRM applications.