Effect of CoFe2O4 content in iron-cobalt bimetallic catalysts on the activity of methane decomposition for hydrogen production

This study employed nonahydrate ferric nitrate and hexahydrate cobalt nitrate as precursors to fabricate catalysts via calcination, varying the iron-cobalt molar ratios (1: 5, 3: 4, 1: 1, 4: 3, 5: 1). It identified the optimal ratio for catalytic decomposition of methane (CDM) performance. Furthermore, adjusting the calcination temperature enabled control over the spinel content in catalysts with the optimal Fe: Co ratio (3: 4), resulting in a range of single and bimetallic catalysts with diverse spinel contents. Comparative analysis revealed the superior performance of bimetallic catalysts compared to single-metal counterparts. Specifically, under the conditions of 800 °C and GHSV 6 L/(g cat. ·h), Fe 3 Co 4 -700 °C achieved a maximum methane conversion of 75.6%, after maintaining a CDM test for 6 h, there is no decrease in stability. This is because the synergistic effect of Fe and Co bimetallic in the Fe 3 Co 4 -700 °C catalyst facilitates the transfer of charges between the bimetals, alters the surface charge density of the catalyst, enhances the electron donation capability of active sites, thereby favoring the adsorption and cracking processes of methane. XRD indicates that this catalyst with smaller crystallite size benefits the dispersion of catalytic active sites, thus improving the CDM performance. Results underscored the significant impacts of calcination temperature and metal ratio on the catalyst's spinel content and crystallite size. Characterization of spent catalysts unveiled carbon products primarily comprising carbon nano-onions, graphite, and carbon nanotubes, with the optimal catalyst yielding 5.8 g C /g cat. . Increasing calcination temperatures facilitated the formation of the spinel phase. At 150 °C, the Fe: Co (3: 4) catalyst had minimal spinel content, whereas at 300 °C, 700 °C, and 1000 °C, the contents are 9%, 11%, and 24%, respectively. Notably, at 1500 °C, the spinel content dramatically surged to 62%. The relationship between spinel content and spent catalyst crystallite size is not linear, the smaller crystal size is more conducive to the dispersion of catalytic active sites, thereby improving the CDM performance. Catalysts without spinel doping exhibited a crystallite size of around 32.2 nm, which decreased to 25.6 nm with 11% spinel content, and increased to 42.7 nm with 62% content. These findings yield profound insights into the influence of calcination temperature and iron cobalt ratios on catalyst performance, providing valuable guidance for the production of efficient CDM catalysts.