Subsurface Carbon as a Selectivity Promotor to Enhance Catalytic Performance in Acetylene Semihydrogenation

Oxygen-bridged Schottky junction in ZnO-Ni3ZnC0.7 promotes photocatalytic reduction of CO2 to CO: Steering charge flow and modulating electron density of active sites

Developing carbon dioxide (CO2) photocatalysts from transition metal carbides (TMCs) with abundant active sites, modulable electron cloud density, as well as low cost and high stability is of great significance for artificial photosynthesis. Building an efficient electron transfer channel between the photo-excitation site and the reaction-active site to extract and steer photo-induced electron flow is necessary but challenging for the highly selective conversion of CO2. In this study, we achieved an oxygen-bridged Schottky junction between ZnO and Ni3ZnC0.7 (denoted as Znoxide-O-ZnTMC) through a ligand-vacancy strategy of MOF. The ZnO-Ni3ZnC0.7 heterostructure integrates the photo-exciter (ZnO), high-speed electron transport channel (Znoxide-O-ZnTMC), and reaction-active species (Ni3ZnC0.7), where Znoxide-O-ZnTMC facilitates the transfer of excited electrons in ZnO to Ni3ZnC0.7. The Zn atoms in Ni3ZnC0.7 serve as electron-rich active sites, regulating the CO2 adsorption energy, promoting the transformation of *COOH to CO, and inhibiting H2 production. The ZnO-Ni3ZnC0.7 shows a high CO yield of 2674.80 μmol g-1h-1 with a selectivity of 93.40 % and an apparent quantum yield of 18.30 % (λ = 420 nm) with triethanolamine as a sacrificial agent. The CO production rate remains at 96.40 % after 18 h. Notably, ZnO-Ni3ZnC0.7 exhibits a high CO yield of 873.60 μmol g-1h-1 with a selectivity of 90.20 % in seawater.

Cu-Pd bimetal-decorated siloxene nanosheets for semi-hydrogenation of acetylene

Metallic Pd has been proved highly promising when paired with Cu for industrially important acetylene semi-hydrogenation. Herein, we demonstrate that high-surface-area siloxene can feasibly enable alloying between Pd and Cu via room-temperature reduction with Si-H bonds. Unprecedentedly small Cu nanoparticles with isolated Pd were in situ loaded on siloxene, addressing the core problem of low selectivity of Pd and low activity of Cu. This devised structure outclassed the traditional impregnated SiO2 in every aspect of the catalytic performance for the semi-hydrogenation of acetylene under industry conditions, with a 91% acetylene conversion and an impressive 93% selectivity to ethylene at 200 °C, and showed long-term stability with negligible activity decay at this harsh temperature. This work provides new insights for the design of economic bimetallic loaded catalysts for balancing the activity-selectivity dilemma, demonstrating the viability of siloxene as both a synthetic reagent and a carrier material for efficient catalysis.

Enhancing heterogeneous Fenton-like catalysis through pyrrolidine modification of Fe2O3-CuO composites with oxygen-vacancy defects

Enhancing the generation of reactive hydroxyl radicals (•OH) is crucial for overcoming the limitations of the low reactivity of heterogeneous Fenton Fe-based catalysts. Researchers have explored various methods to modify catalyst structures to enhance reactivity, yet often at the expense of stability. Herein, suitable carbon and nitrogen-codoped Fe2O3-CuO composites were synthesized via pyrolysis method, demonstrating high Fenton reaction activity and remarkable stability. Experimental findings and density functional theory calculations (DFT) revealed that the presence of oxygen vacancies on the catalyst surface facilitated an increase in exposed FeNC active sites, promoting electron transfer and the accelerating the rate of •OH generation. Moreover, carbon and nitrogen, particularly in the form of pyrrole nitrogen bonded to Fe imparted exceptional stability to the FeNC active sites, mitigating their dissolution. Additionally, the Fe-based catalysts exhibited strong magnetism, enabling easy separation from the reaction solution while maintaining a high degradation efficiency for various organic pollutants, even in the presence of multiple anions. Furthermore, a comprehensive mechanism for methylene blue (MB) degradation was identified, enhancing the potential practical applications of these catalysts.

Active site tuning based on pseudo-binary alloys for low-temperature acetylene semihydrogenation

The development of an efficient catalytic system for low-temperature acetylene semihydrogenation using nonnoble metals is important for the cost-effective production of polymer-grade pure ethylene. However, it remains challenging owing to the intrinsic low activity. Herein, we report a flexibly tunable catalyst design concept based on a pseudo-binary alloy, which enabled a remarkable enhancement in the catalytic activity, selectivity, and durability of a Ni-based material. A series of (Ni1-xCux)3Ga/TiO2 catalysts exhibiting L12-type pseudo-binary alloy structures with various Cu contents (x = 0.2, 0.25, 0.33, 0.5, 0.6, and 0.75) were prepared for active site tuning. The optimal catalyst, (Ni0.8Cu0.2)3Ga/TiO2, exhibited outstandingly high catalytic activity among reported 3d transition metal-based systems and excellent ethylene selectivity (96%) and long-term stability (100 h) with near full conversion even at 150 °C. A mechanistic study revealed that Ni2Cu hollow sites on the (111) surface weakened the strong adsorption of acetylene and vinyl adsorbate, which significantly accelerated the hydrogenation process and inhibited undesired ethane formation.

Hierarchical Ohmic Contact Interface Engineering for Efficient Hydrazine-Assisted Hydrogen Evolution Reaction

Hydrazine oxidation reaction coupled with hydrogen evolution reaction (HER) is an effective strategy to achieve low energy water splitting for hydrogen production. In order to realize the application of hydrazine-assisted HER system, researchers have been focusing on the development of electrocatalysts with integrated dual active sites, while the performance under high current density is still unsatisfying. In this work, hierarchical Ohmic contact interface engineering is designed and used as a bridge between the NiMo and Ni2 P heterojunction toward industrial current density applications, with the charge transfer impedance greatly eliminated via such a pathway with low energy barrier. As a proof-of-concept, the importance of charge redistribution and energy barrier at the Ohmic contact interface is investigated by significantly reducing the voltage of overall hydrazine splitting (OHzS) at high current density. Intriguingly, the NiMo/Ni2 P hierarchical Ohmic contact heterojunction can drive current densities of 100 and 500 mA cm-2 with only 181 and 343 mV cell voltage in the OHzS electrolyzer with high electrocatalytic stability. The proposed hierarchical Ohmic contact interface engineering paves new avenue for hydrogen production with low energy consumption.

In-Situ-Formed Potassium-Modified Nickel-Zinc Carbide Boosts Production of Higher Alcohols beyond CH4 in CO2 Hydrogenation

Ni-based catalysts have been widely studied in the hydrogenation of CO2 to CH4 , but selective and efficient synthesis of higher alcohols (C2+ OH) from CO2 hydrogenation over Ni-based catalyst is still challenging due to successive hydrogenation of C1 intermediates leading to methanation. Herein, we report an unprecedented synthesis of C2+ OH from CO2 hydrogenation over K-modified Ni-Zn bimetal catalyst with promising activity and selectivity. Systematic experiments (including XRD, in situ spectroscopic characterization) and computational studies reveal the in situ generation of an active K-modified Ni-Zn carbide (K-Ni3 Zn1 C0.7 ) by carburization of Zn-incorporated Ni0 , which can significantly enhance CO2 adsorption and the surface coverage of alkyl intermediates, and boost the C-C coupling to C2+ OH rather than conventional CH4 . This work opens a new catalytic avenue toward CO2 hydrogenation to C2+ OH, and also provides an insightful example for the rational design of selective and efficient Ni-based catalysts for CO2 hydrogenation to multiple carbon products.

A solid-state synthetic strategy toward nickel-based bimetallic interstitial compounds (MNi3Cx, M = Zn, In, Ga)

Bimetallic interstitial compounds with unique geometric properties have attracted increasing attention in energy-related fields and diverse chemical transformations. Current synthesis of these compounds generally involves at least one wet-chemistry step with the use of various solvents to prepare the bimetallic precursors, and no universal protocols for different compositions are yet available. Herein, a novel synthetic strategy toward a platform of nickel-based bimetallic interstitial compounds with the formula MNi3Cx, M = Zn, In, and Ga, was developed based on a straightforward solid-state transformation, i.e., simply annealing the hydroxides of the respective metals in the presence of different carbon precursors (cyanamide, dicyandiamide, melamine, and urea) in a hydrogen stream. The key process parameters influencing the compositions of the final products are studied and the formation mechanism is discussed based on advanced characterization techniques. Powder X-ray diffraction reveals MNi3Cx as a single phase and electron microscopy shows that the MNi3Cx particles are covered with N-doped carbon shells. Extrapolation to other bimetallic interstitial compounds failed when following the above protocol, and the successful examples are linked to the formation of the corresponding bimetallic alloys in the absence of carbon precursors. When evaluated for the selective hydrogenation of dimethyl oxalate, both InNi3C0.5 and ZnNi3C0.7 show comparable high activity. While ZnNi3C0.7 delivers the highest selectivity for methyl glycolate, tunable methyl glycolate and ethylene glycol are formed on InNi3C0.5. In general, this facile solvent-free strategy affords an interesting scaffold to fabricate more advanced multi-metallic interstitial compounds with broad applications.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Mechanism driven design of trimer Ni1Sb2 site delivering superior hydrogenation selectivity to ethylene

Mechanism driven catalyst design with atomically uniform ensemble sites is an important yet challenging issue in heterogeneous catalysis associated with breaking the activity-selectivity trade-off. Herein, a trimer Ni₁Sb₂ site in NiSb intermetallic featuring superior selectivity is elaborated for acetylene semi-hydrogenation via a theoretical guidance with a precise synthesis strategy. The trimer Ni₁Sb₂ site in NiSb intermetallic is predicted to endow acetylene reactant with an adequately but not excessively strong σ-adsorption mode while ethylene product with a weak π-adsorption one, where such compromise delivers higher ethylene formation rate. An in-situ trapping of molten Sb by Ni strategy is developed to realize the construction of Ni₁Sb₂ site in the intermetallic P6₃/mmc NiSb catalysts. Such catalyst exhibits ethylene selectivity up to 93.2% at 100% of acetylene conversion, significantly prevailing over the referred Ni catalyst. These insights shed new lights on rational catalyst design by taming active sites to energetically match targeted reaction pathway.

Designing atomically uniform ensemble sites for matching targeted reaction pathway is important yet challenging in heterogeneous catalysis. Here, the authors fabricate a trimer Ni₁Sb₂ site featuring superior selectivity for acetylene semi-hydrogenation via a mechanism-driven design strategy.