The phenomenon of "dead" metal in heterogeneous catalysis: opportunities for increasing the efficiency of carbon-supported metal catalysts

This review addresses the largely overlooked yet critical issue of "dead" metal in heterogeneous metal catalysts. "Dead" metal refers to the fraction of metal in a catalyst that remains inaccessible to reactants, significantly reducing the overall catalyst performance. As a representative example considered in detail here, this challenge is particularly relevant for carbon-supported metal catalysts, extensively employed in research and industrial settings. We explore key factors contributing to the formation of "dead" metal, including the morphology of the support, metal atom intercalation within the support layers, encapsulation of metal nanoparticles, interference by organic molecules during catalyst preparation, and dynamic behavior under microwave irradiation. Notably, the review outlines a series of strategic approaches to mitigate the occurrence of "dead" metal during catalyst preparation, thus boosting the catalyst efficiency. The knowledge gathered is important for enhancing the preparation of catalysts, especially those containing precious metals. Beyond the practical implications for catalyst design, this study introduces a novel perspective for understanding and optimizing the catalyst performance. The insights are expected to broadly impact different scientific disciplines, empowered with heterogeneous catalysis and driving innovation in energy, environmental science, and materials chemistry, among others. Exploring the "dead" metal phenomenon and potential mitigation strategies brings the field closer to the ultimate goal of high-efficiency, low-cost catalysis.

Catalysts Based on Ni(Mg)Al-Layered Hydroxides Prepared by Mechanical Activation for Furfural Hydrogenation

Ni(Mg)Al-layered hydroxides with molar ratios of (Ni + Mg)/Al = 2, 3, 4 and Ni/(Ni + Mg) = 0.1, 0.3, 0.5, 0.7 were synthesized by mechanochemical activation. It has been proven that the phase composition of the samples was presented by a single hydrotalcite phase up to Ni/(Ni + Mg) = 0.5. For the first time, catalysts based on Ni(Mg)Al-layered hydroxides prepared by a mechanochemical route have been studied in the reaction of furfural hydrogenation. The correlation between furfural conversion, the selectivity of the products, and the composition of the catalysts was established. The effect of phase composition, surface morphology, and microstructure on the activity of the catalysts was shown by XRD, SEM, and TEM. It was found that catalysts with Ni/(Ni + Mg) = 0.5 have the highest furfural conversion. Herewith, the product selectivity can be regulated by the (Ni + Mg)/Al ratio.