Carbon Dioxide Hydrogenation over Supported Ni and Ru Catalysts

Understanding and Harnessing Nanoscale Immiscibility in Ru-In Alloys for Selective CO2 Hydrogenation

Bimetallic alloys made from immiscible elements are characterized by their tendency to segregate on the macroscopic scale, but their behavior is known to change at the nanoscale. Here, we demonstrate that in the Ru-In system, In atoms preferentially decorate the surface of 6 nm Ru nanoparticles, forming Ru-In superficial immiscible alloys. This surface decoration dramatically affects the catalytic performance of the system, even at small atomic fractions of In added to Ru. The interfaces between Ru and In enabled unexplored methanol productivity from CO2 hydrogenation, which outperformed not only the individual constituents but also ordered RuIn3 intermetallic alloys. Our work highlights that the formation of superficial immiscible alloys could offer new insights into the understanding and design of heterogeneous catalysts.

Highly Active Ce- and Mg-Promoted Ni Catalysts Supported on Cellulose-Derived Carbon for Low-Temperature CO2 Methanation

The CO₂ methanation performance of Mg- and/or Ce-promoted Ni catalysts supported on cellulose-derived carbon (CDC) was investigated. The samples, prepared by biomorphic mineralization techniques, exhibit pore distributions correlated to the particle sizes, revealing a direct effect of the metal content in the textural properties of the samples. The catalytic performance, evaluated as CO₂ conversion and CH₄ selectivity, reveals that Ce is a better promoter than Mg, reaching higher conversion values in all of the studied temperature range (150-500 °C). In the interval of 350-400 °C, Ni-Mg-Ce/CDC attains the maximum yield to methane, 80%, reaching near 100% CH₄ selectivity. Ce-promoted catalysts were highly active at low temperatures (175 °C), achieving 54% CO₂ conversion with near 100% CH₄ selectivity. Furthermore, the large potential stability of the Ni-Mg-Ce/CDC catalyst during consecutive cycles of reaction opens a promising route for the optimization of the Sabatier process using this type of catalyst.

Support Effects on the Activity of Ni Catalysts for the Propane Steam Reforming Reaction

The catalytic performance of supported Ni catalysts for the propane steam reforming reaction was investigated with respect to the nature of the support. It was found that Ni is much more active when supported on ZrO₂ or YSZ compared to TiO₂, whereas Al₂O₃₋ and CeO₂-supported catalysts exhibit intermediate performance. The turnover frequency (TOF) of C₃H₈ conversion increases by more than one order of magnitude in the order Ni/TiO₂ < Ni/CeO₂ < Ni/Al₂O₃ < Ni/YSZ < Ni/ZrO₂, accompanied by a parallel increase of the selectivity toward the intermediate methane produced. In situ FTIR experiments indicate that CH_x species produced via the dissociative adsorption of propane are the key reaction intermediates, with their hydrogenation to CH₄ and/or conversion to formates and, eventually, to CO, being favored over the most active Ni/ZrO₂ catalyst. Long term stability test showed that Ni/ZrO₂ exhibits excellent stability for more than 30 h on stream and thus, it can be considered as a suitable catalyst for the production of H₂ via propane steam reforming.