Alkali ions secure hydrides for catalytic hydrogenation

Embedding ruthenium nanoparticles in the shell layer of titanium zirconium oxide hollow spheres to catalyze the degradation of alkali lignin under mild condition

To catalyze the degradation of lignin in refractory wastewater efficiently, a new nanocomposite with Ru nanoparticles embedded on the surface of TiZrO₄ hollow spheres was fabricated with three method a "sol-gel + calcination + vacuum-impregnation" template method, and the unique binary composition of TiZrO₄/Ru prevented the aggregation of Ru and keep its high activity. During 3-h catalytic-oxidation at 160 °C and 2.0 MPa O₂, 98% alkali lignin was degraded and 70% organic carbon was mineralized with the catalysis of TiZrO₄/Ru, while the values were only 50% and 25% without analysts. The catalyst increased the catalytic-oxidation rate constant k₁ (h^-1) of alkali lignin from 0.282 h^-1 to 1.175 h^-1 because of high-efficiency hydroxyl radical production, as determined by EPR. LC-OCD showed that the catalyst decomposed alkali lignin with molecular weight 1-2 kDa to small molecules. Butyl acetate was the main intermediate product, which should be derived from the auto synthesis of butanol and acetic acid. In addition to high conversion efficiency, the catalyst had good stability with 95% capability after five cycles. In real biogas slurry treatment, an increase of biochemical to COD ratio from 0.28 to 0.51, with obvious decoloration, indicated TiZrO₄/Ru enhanced the biodegradability of the refractory wastewater significantly.

Highly selective and robust single-atom catalyst Ru1/NC for reductive amination of aldehydes/ketones

Single-atom catalysts (SACs) have emerged as a frontier in heterogeneous catalysis due to the well-defined active site structure and the maximized metal atom utilization. Nevertheless, the robustness of SACs remains a critical concern for practical applications. Herein, we report a highly active, selective and robust Ru SAC which was synthesized by pyrolysis of ruthenium acetylacetonate and N/C precursors at 900 °C in N₂ followed by treatment at 800 °C in NH₃. The resultant Ru₁-N₃ structure exhibits moderate capability for hydrogen activation even in excess NH₃, which enables the effective modulation between transimination and hydrogenation activity in the reductive amination of aldehydes/ketones towards primary amines. As a consequence, it shows superior amine productivity, unrivalled resistance against CO and sulfur, and unexpectedly high stability under harsh hydrotreating conditions compared to most SACs and nanocatalysts. This SAC strategy will open an avenue towards the rational design of highly selective and robust catalysts for other demanding transformations.

Single-atom catalyst (SAC) has emerged as a frontier in heterogeneous catalysis yet its robustness remains a critical concern. Here, a highly active, selective and robust Ru₁-N₃ SAC is explored for a challenging reaction, reductive amination of aldehydes/ketones for synthesis of primary amines.

Insights into the Interfacial Effects in Heterogeneous Metal Nanocatalysts toward Selective Hydrogenation

Heterogeneous metal catalysts are distinguished by their structure inhomogeneity and complexity. The chameleonic nature of heterogeneous metal catalysts have prevented us from deeply understanding their catalytic mechanisms at the molecular level and thus developing industrial catalysts with perfect catalytic selectivity toward desired products. This Perspective aims to summarize recent research advances in deciphering complicated interfacial effects in heterogeneous hydrogenation metal nanocatalysts toward the design of practical heterogeneous catalysts with clear catalytic mechanism and thus nearly perfect selectivity. The molecular insights on how the three key components (i.e., catalytic metal, support, and ligand modifier) of a heterogeneous metal nanocatalyst induce effective interfaces determining the hydrogenation activity and selectivity are provided. The interfaces influence not only the H₂ activation pathway but also the interaction of substrates to be hydrogenated with catalytic metal surface and thus the hydrogen transfer process. As for alloy nanocatalysts, together with the electronic and geometric ensemble effects, spillover hydrogenation occurring on catalytically "inert" metal by utilizing hydrogen atom spillover from active metal is highlighted. The metal-support interface effects are then discussed with emphasis on the molecular involvement of ligands located at the metal-support interface as well as cationic species from the support in hydrogenation. The mechanisms of how organic modifiers, with the ability to induce both 3D steric and electronic effects, on metal nanocatalysts manipulate the hydrogenation pathways are demonstrated. A brief summary is finally provided together with a perspective on the development of enzyme-like heterogeneous hydrogenation metal catalysts.