This review summarizes the importance of nanoporous materials and their fascinating structural properties with respect to the catalytic and photocatalytic reduction of CO₂ to methane, toward achieving a sustainable energy supply. The importance of catalysis as a bridge step for advanced energy systems and the associated environmental issues are stressed. A deep understanding of the fundamentals of these nanoporous solids is necessary to improve the design and efficiency of CO₂ methanation. The role of the support dominates the design in terms of developing an efficient methanation catalyst, specifically with respect to ensuring enhanced metal dispersion and a long catalyst lifetime. Nanoporous materials provide the best supports for Ni, Ru, Rh, Co, Fe particles because they can prevent sintering and deactivation through coking, which otherwise blocks the metal surface as carbon accumulates. This review concludes with the major challenges facing the CO₂ methanation by nanoporous materials for fuel applications.

Surface-phosphated NiO catalysts with different phosphorus contents were prepared and used for ethane oxidative dehydrogenation (ODH) in the temperature range from 300 to 425 °C. The catalysts were characterized by nitrogen adsorption at −196 °C, XRD, ICP-OES, XPS, TEM, and Raman spectroscopy. They were also characterized by in situ electrical conductivity measurements at various temperatures and oxygen partial pressures, and the temporal response of the electrical conductivity to sequential exposure to air, an ethane–air mixture (reaction mixture) and pure ethane was recorded under conditions similar to those employed in the catalytic experiments. Adding increasing amounts of phosphorus to NiO changes its physicochemical characteristics; specifically, both the concentration and mobility of the surface lattice O⁻ species in the NiO material decrease considerably, affecting its catalytic performance in ethane ODH. Thus, increasing the P content in NiO leads to a decrease in its catalytic activity with an increase in its ODH selectivity at the expense of total oxidation selectivity in the temperature range studied.

Direct hydrothermal synthesis (HT), template ion-exchange (TIE) and molecular dispersion (MD) approaches were used to introduce manganese species into MCM-48-type mesoporous materials. The tungsten was highly dispersed within the channels of mesoporous MnMCM-48 samples by chemical grafting (CG) via a liquid–solid reaction. The prepared manganesosilicate and tungstenomanganesosilicate MCM-48-type mesoporous materials were characterized by physico-chemical techniques, including TEM, N₂ sorption, XRD, XPS, UV-Vis and elemental analysis. The physico-chemical characterization revealed that all of the samples retained a high surface area, a regular cubic mesoporosity and that the Mn and W were highly dispersed. The higher unit cell parameter/pore wall thickness values of the MnMCM-48 and WMnMCM-48 samples relative to that of pure MCM-48 indicate the incorporation of Mn and W into the framework/channels of MCM-48. The Mn and W species existed as isolated sites in the framework/extra-framework or as monomolecular species. No bulk manganese or tungsten was observed outside the MCM-48-type mesoporous materials. The coexistence of Mn²⁺, Mn³⁺ or/and W⁶⁺ was evidenced by XPS and UV-Vis spectroscopic measurements. The catalytic activities of these samples were studied with respect to the conversion of methylcyclopentane (MCP) in reductive media as a function of Mn loading and reaction temperature (200–500 °C). Whatever the manganese content and irrespective of the temperature of reaction, the MnMCM-48 mesoporous samples did not exhibit catalytic activity, which suggests that the electrophilic manganese oxygen species, operative over all the samples, were inactive sites for the conversion of MCP. The addition of tungsten favored catalytic activity. When the WMnMCM-48 was not calcined, only the methane (C₁) cracking product was observed to be formed by successive rupture of C–C bonds starting at 400 °C. When the WMnMCM-48 was calcined, ring-opening products formed by the C–C rupture, at substituted and unsubstituted carbon atoms, were observed starting at 400 °C. This behavior is associated with a symbiotic process between the MnMCM-48 support and the W nanoparticles.