The role of the counterion in metal-catalyzed reactions can be crucial as this often-unconsidered component of the catalyst can modify the performance of the catalyst and influence the reaction rate and/or selectivity of the transformation under study. Herein, we disclose the effects of counterion variation in cationic halogen bond-assembled Rh(I) catalysts in the hydroboration reaction of terminal alkynes, which leads to rather elusive branched (or internal) hydroboration products. Our studies showed that the higher the coordination ability of the counterion, the higher the activity and selectivity toward the hydroboration products. This observation was demonstrated by catalytic and spectroscopic (NMR, IR and X-ray) studies. An array of structurally diverse alkynes was efficiently transformed into the corresponding hydroboration products employing the highest performing catalyst XBphos-Rh-OTf. The practicality of our synthetic method was demonstrated by developing one-pot hydroboration/Csp2-Csp2 coupling processes.

Mononuclear copper complexes relevant to the active site of copper nitrite reductases (CuNiRs) are known to be catalytically active for the reduction of nitrite. Yet, their catalytic mechanism has thus far not been resolved. Here, we provide a complete description of the electrocatalytic nitrite reduction mechanism of a bio-inspired CuNiR catalyst Cu(tmpa) (tmpa = tris(2-pyridylmethyl)amine) in aqueous solution. Through a combination of electrochemical studies, reaction kinetics, and density functional theory (DFT) computations, we show that the protonation steps take place in a stepwise manner and are decoupled from electron transfer. The rate-determining step is a general acid-catalyzed protonation of a copper-ligated nitrous acid (HNO2) species. In view of the growing urge to convert nitrogen-containing compounds, this work provides principal reaction parameters for efficient electrochemical nitrite reduction. This contributes to the investigation and development of nitrite reduction catalysts, which is crucial to restore the biogeochemical nitrogen cycle.

Supported Pd catalysts are most promising in heterogeneous CO2 hydrogenation into formic acid (FA), while their applications are immensely restricted due to relatively poorer activity and lower utilization of Pd atoms compared to homogeneous catalysts. Herein, anatase TiO2{101}-supported Pd and PdAg catalysts were used for the hydrogenation of CO2 into FA. The electronic properties of supported Pd species were finely tuned by altering the Pd contents and Pd:Ag ratios. As the Pd loading decreased, the weakened metallicity limited the hydrogenation property, resulting in the steep decline of the reaction rate. The introduction of Ag not only improves the metallicity of supported Pd species but also promotes the utilization of Pd atoms, jointly contributing to the reaction activity. However, more Ag loadings adversely suppress the H-spillover effect that blocks the hydrogenation process. Consequently, an optimal Pd:Ag mole ratio of 5 over the Pd0.2Ag0.04/TiO2 catalyst with a Pd–Ag coordination number of 2 exhibits a very high FA yield, affording a value of 1429 h–1. In situ DRIFTS spectra coupled with kinetics results confirm the reaction proceeding through the bicarbonate intermediate, in which hydrogenation toward formate is the rate-determining step. These results not only deepen the fundamental understanding of supported Pd catalysts in CO2 hydrogenation but also broaden the concept of morphology engineering strategy for developing efficient and low-cost heterogeneous catalysts for FA production.

Large-scale development of electrochemical cells is currently hindered by the lack of Earth-abundant electrocatalysts with high catalytic activity, product selectivity, and interfacial mass transfer. Herein, we developed an electrocatalyst fabrication approach which responds to these requirements by irradiating plasmonic titanium nitride (TiN) nanocubes self-assembled on a carbon gas diffusion layer in the presence of polymeric binders. The localized heating produced upon illumination creates unique conditions for the formation of TiN/F-doped carbon hybrids that show up to nearly 20 times the activity of the pristine electrodes. In alkaline conditions, they exhibit enhanced stability, a maximum H2O2 selectivity of 90%, and achieve a H2O2 productivity of 207 mmol gTiN–1 h–1 at 0.2 V vs RHE. A detailed electrochemical investigation with different electrode arrangements demonstrated the key role of nanocomposite formation to achieve high currents. In particular, an increased TiOxNy surface content promoted a higher H2O2 selectivity, and fluorinated nanocarbons imparted good stability to the electrodes due to their superhydrophobic properties.

Fe-modified BiVO4 represents a promising anode material for the photoelectrochemical (PEC) oxygen evolution reaction in neural electrolytes, the bottleneck reaction in PEC water splitting. To reveal the catalytic role of Fe in this composite catalytic system, here we utilize combined theoretical and experimental techniques to identify the location and structure of FeOx phases and optimize the catalytic performance. By using the machine-learning interface search method, we screen out a coherent ε-FeOOH1.5(011)/BiVO4(001) interface from thousands of likely interface candidates. The interface has a low formation energy (0.74 J/m2), a narrow band structure (∼1.6 eV), and desirable catalytic activity (reaction barrier ∼ 0.64 eV) when the ε-FeOOH1.5 overlayer is two atomic layers thick. Guided by the theoretical findings, our orthogonal PEC experiments are performed to identify the optimal synthetic conditions. The best PEC activity reaches 5.4 mA/cm2 (1.23 V vs reversible hydrogen electrode) when using FeSO4 as the precursor with the chemical bath method at 40 °C for 4 h, which is ∼0.9 mV/ cm2 higher compared to the previous experiment. By analyzing transmission electron microscopy (TEM) pictures and performing TEM simulations, we confirm that the grass-like FeOx structures grown on BiVO4 are ε-FeOOH crystals as predicted by theory.

Understanding the reduction mechanism of ZnO/CuOx interfaces by hydrogen is of great importance in advancing the performance of industrial catalysts used for CO and CO2 hydrogenation to oxygenates, the water-gas shift, and the reforming of methanol. Here, the reduction of pristine and ZnO-modified CuOx/Cu(111) by H2 was investigated using ambient-pressure scanning tunneling microscopy (AP-STM), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and density functional theory (DFT). The morphological changes and reaction rates seen for the reduction of CuOx/Cu(111) and ZnO/CuOx/Cu(111) are very different. On CuOx/Cu(111), perfect “44” and “29” structures displayed a very low reactivity toward H2 at room temperature. A long induction period associated with an autocatalytic process was observed to enable the reduction by the removal of chemisorbed nonlattice oxygen initially and lattice oxygen sequentially at the CuOx–Cu interface, which led to the formation of oxygen-deficient “5–7” hex and honeycomb structures. In the final stages of the reduction process, regions of residual oxygen species and metallic Cu were seen. The addition of ZnO particles to CuOx/Cu(111) opened additional reaction channels. On the ZnO sites, the dissociation of H2 was fast and H adatoms easily migrated to adjacent regions of copper oxide. This hydrogen spillover substantially enhanced the rate of oxygen removal, resulting in the rapid reduction of the copper oxide located in the periphery of the zinc oxide islands with no signs of the reduction of ZnO. The deposited ZnO completely modified the dynamics for H2 dissociation and hydrogen migration, providing an excellent source for CO2 hydrogenation processes on the inverse oxide/metal system.

Using first-principles calculations, we showed that the monoclinic WO3(001) preferentially forms a reconstructed monolayer on the anatase TiO2(001) surface. We thoroughly examined the structure of the WO3/TiO2 surface under ambient conditions, i.e., in equilibrium with gas-phase O2/H2O or H2/H2O under a range of pressure and temperature or in aqueous solution under a range of pH and electrochemical potential. Based on the WO3/TiO2 surface structures at different potentials, we proposed the proton-coupled electron-transfer (PCET) reaction pathway during charging and oxygen reduction reaction (ORR) pathways during discharging, which account for its reversible electron storage ability. With electronic structure analysis, we depicted the charge separation effect of WO3 on TiO2 and the electron storage effect of WO3.

Plasmonic nanoparticles (PNPs) constitute a significant category of photoresponsive materials whose exploitation in photoboosted catalysis is a forward-looking strategy. Here, it is demonstrated that photoexcited core–shell Ag0@SiO2 PNPs can dramatically enhance formic acid dehydrogenation (FADH), catalyzed by the molecular catalyst [Fe(BF4)2·6H2O/P(CH2CH2PPh2)3, PP3]. In the presence of photoexcited Ag0@SiO2 PNPs, the optimized catalytic system [(Fe/PP3)/HCOOH/Ag0@SiO2/hv] achieves an almost 10-fold increase of the H2-gas-production rate vs [(Fe/PP3)/HCOOH] (173 vs 17 mL H2 min–1, using 12.5 μmol of catalyst), while the turnover numbers (TONs) are boosted by ∼400% (35,643 vs 9615) and the turnover frequencies (TOFs) by ∼600% (17,821 h–1 vs 2885 h–1). Selective excitation at wavelengths (λex) spanning the photoresponse profile of Ag0@SiO2 NPs demonstrates that the FADH enhancement is maximal at λex = 405 nm, which is at the peak of the photoplasmonic response of Ag0@SiO2 NPs. Monitoring of the solution potential (Eh) under catalytic conditions reveals that the photoexcitation of Ag0@SiO2 PNPs injects hot electrons, as reducing agents, into the reaction solution. Varying the SiO2-shell thickness of Ag0@SiO2 PNPs in the range of 3–5 nm allowed control of the hot-electron injection rates and the ensuing FADH rates. The present results are discussed in the context of the catalytic cycle of the [(Fe/PP3)/HCOOH] system, where plasmonically generated hot electrons boost H2 production via FADH by molecular catalysts, in distinction to the thermoplasmonic effects that seem to play a secondary role. The present H2-production rate data demonstrate the possibility to approach industrial-scale H2-production rates via FADH, using low-cost Fe-based catalysts and no sacrificial cocatalysts. We consider that the phenomenon exemplified herein for a standard molecular-catalysis system, such as [(Fe/PP3)/HCOOH], can be valid for many other pertinent molecular FADH catalysts.

The catalytic conversion of greenhouse gas CO2 into valuable chemicals is a vital goal toward carbon balance and sustainability. In recent decades, the chemical fixation of CO2 into cyclic carbonates has gained much attention. In this work, a series of zinc complexes bearing tetradentate aminopyridine (N4) ligands have been synthesized and characterized. These zinc complexes were applied to the coupling of CO2 with epoxides in excellent yields and with a broad substrate scope under cocatalyst- and solvent-free conditions. Moreover, the zinc catalysts could be readily recovered and reused five times without an obvious loss in catalytic activity. Based on spectroscopic characterizations and experimental results, catalyst Zn-3 (DAP-ZnBr2, DAP = 1,4-bis(2-pyridymethyl)-1,4-diazepane) has been found to be a multifunctional catalyst because of the presence of a Lewis acidic zinc center and a nuclephilic halide anion, and one pyridine is released for the activation of CO2 during the reaction.

Hydrogen is an attractive energy carrier because of its high energy density and clean emission. Herein, we report the construction of Ptδ+–O(H)–Ti3+ species on titania-supported Pt nanoparticles with strong metal–support interaction (SMSI), which boost the catalytic production of hydrogen from methanol steam reforming and water-gas shift at low temperatures. Characterizations of in-situ FTIR spectroscopy confirmed the formation of Ptδ+–O(H)–Ti3+ species, which resulted from the reduction of titania and dissociation of water at the Pt–titania interfaces. Compared with the general titania-supported Pt NPs without SMSI, the Pt/TiO2 with SMSI exhibited an improved hydrogen production rate by 9 times, and the CO concentration in the effluent was lower than 200 ppm. These findings gave a model for exploring the structure-performance interplay and provided an efficient strategy to optimize the catalysts to accelerate the production of hydrogen.

Copper-based hydrogen evolution electrocatalysts are promising materials to scale-up hydrogen production due to their reported high current densities; however, electrode durability remains a challenge. Here, we report a facile, cost-effective, and scalable synthetic route to produce Cu2–xS electrocatalysts, exhibiting hydrogen evolution rates that increase for ∼1 month of operation. Our Cu2–xS electrodes reach a state-of-the-art performance of ∼400 mA cm–2 at −1 V vs RHE under mild conditions (pH 8.6), with almost 100% Faradaic efficiency for hydrogen evolution. The rise in current density was found to scale with the electrode electrochemically active surface area. The increased performance of our Cu2–xS electrodes correlates with a decrease in the Tafel slope, while analyses by X-ray photoemission spectroscopy, operando X-ray diffraction, and in situ spectroelectrochemistry cooperatively revealed the Cu-centered nature of the catalytically active species. These results allowed us to increase fundamental understanding of heterogeneous electrocatalyst transformation and consequent structure–activity relationship. This facile synthesis of highly durable and efficient Cu2–xS electrocatalysts enables the development of competitive electrodes for hydrogen evolution under mild pH conditions.

Hydrogenation of toluene (TOL) to methylcyclohexane (MCH) is one of the hydrogen carrier systems desired for social integration. Supported Pt nanoparticle catalysts are effective for this application. However, Pt is rare, expensive, and in short supply, limiting its practical applications. Therefore, the key issue for TOL hydrogenation is how to substantially reduce the amount of Pt required for the catalyst. Because a specific ensemble of Pt atoms, that is dominantly formed on the surface of the Pt nanoparticle, is required for achieving higher catalytic performance, there is a limit to the number of precious Pt that can be conserved by simply reducing the particle size. The structure sensitivity established in the existing heterogeneous catalyst so far makes it difficult to design precious metal-conserving catalysts with both high activity and atomic efficiency. Here, a strategy for breaking the above limitations is reported. Our approach uses the heteroatom ensemble (HAE) on Pt single-atom alloyed 3d transition-metal nanoparticle catalysts (Pt1M SAAs, M = Co, Ni, Cu). The role of the TOL fixation/activation site is assigned to the atomic M sites on HAE, whereas the H2-activation site is to the Pt single-atom site on HAE. The atomic-scale division of roles within the HAE improves the efficiency of competitive adsorption of TOL/H2, which is important for boosting TOL hydrogenation. To maximize the synergistic effect at the adjacent sites, the atomic composition, geometric configuration, and electronic state of these active sites as well as the density of the HAE were tuned by the chemical composition and particle size of Pt1M SAAs. High activity was observed on the Pt1Co SAA with a particle size of 1.8 nm and Pt/Co molar ratio of 0.002. The Pt mass-specific activity reached 219 mol/gPt/h, which was 23 times higher than that in a conventional Pt nanoparticle-supported catalyst. Using a set of well-defined Pt1M SAAs, high-angle annular dark-field scanning transmission electron microscopy, Pt LIII-edge X-ray absorption fine structure spectroscopy, coupled with periodic density functional theory and ab initio molecular dynamics simulation, we proved the origin of the structure sensitivity at an atom-to-nanometer scale. The present work sheds light on the significance of regulations of the coordination environment of the Pt single-atom site, atomic composition, and particle size of Pt1M SAA for creating high activity, durability, and Pt-utilization efficiency for catalytic applications relevant to hydrogen carrier systems.

The Z-scheme heterostructure is a highly promising photocatalyst for its unique electronic structure. However, a thorough examination of the heterostructure design space through experimental or computational means is prohibitively expensive. Here, we propose a highly efficient data-driven approach for fast discovering van der Waals (vdW) Z-scheme heterostructures, bypassing the need for costly calculations and experimentation. By conducting high-throughput calculations with the Heyd–Scuseria–Ernzerhof hybrid density functional (HSE06), we first generate a variety of data of electronic structures for 18 experimentally synthesized 2D transition metal dichalcogenides (TMDs) and 20 of 153 heterostructures (constructed with the 18 TMDs). Using these data, we develop an innovative and robust descriptor: Allen “material” electronegativity. Leveraging this descriptor, we identify 27 2D vdW Z-scheme heterostructures from the pool of 153 heterostructures without expensive HSE calculations. We finally refine our findings by selecting six Z-scheme heterostructures with minimal lattice mismatch, further validating them using high-fidelity ab initio calculations and studying their optical absorption. Our research not only paves the way for discovering high-performance Z-scheme photocatalysts using data-driven methods but also contributes a universal charge transfer mechanism for vdW device applications.

An enantiotopic group-selective monosilylation of silanediols using List’s counteranion-directed silylation methodology is reported. A silylium-ion-like silicon electrophile generated from an allylic silane paired with an imidodiphosphorimidate (IDPi) enables the enantioselective discrimination of the two hydroxy groups attached to the prochiral silicon atom. The enantioselectivity achieved in the desymmetrization step is further improved by a subsequent kinetic resolution to arrive at silicon-stereogenic disiloxanes with high enantiocontrol, along with minor amounts of the achiral trisiloxane byproduct.

Transition metal-catalyzed reactions are developed together with ligands. While transition metal-catalyzed photoreactions have been extensively reported in recent years, the development of ligands for photoreactions is limited to only a few cases. Therefore, establishing ligands that shed light on transition metal-catalyzed photoreactions is an important research goal. We successfully synthesized four acridine-containing PNP-pincer ligands and formed transition metal complexes with Ni, Pd, Pt, Cu, and Co. We found that the platinum complex induced photoreactions of olefins under visible light irradiation: transfer hydrogenation, which required only a stoichiometric amount of hydrogen source, and hydroxy/alkoxy alkylation of olefins. These reactions did not proceed with existing well-known ligands, demonstrating that the development of photoreaction-oriented ligands reveals unknown reactivities of transition metals.

Reminiscent to nature’s NAD+/NADH hydride storage and transfer system, we demonstrate here that an iridium complex containing a pyridinium ligand, IrPYE+, is capable of reversibly storing a hydride upon reaction with formate. The hydride in IrPYEH is stable toward air and water, yet it is released in the presence of electrophiles such as acids or carbonyl compounds. The full reversibility of the hydride storage provides access to the hydrogenation procedure that is catalytic in IrPYEH, reaching up to 100,000 turnover numbers and surpassing other related catalysts by several orders of magnitude. With deuterated formate, IrPYED allows for selective deuterium isotope labeling without notable scrambling even in the presence of acids, air, and moisture.

Nitrilases are a class of enzymes that hydrolyze nitriles to carboxylic acids and ammonia. However, as research has progressed, the hydration activities that convert nitriles to amides are also found in nitrilases from different sources, which result in difficulties for high-purity production of carboxylic acids and meanwhile endow the enzyme with potential for valuable amides biosynthesis. In this study, the distance between the residues Cys and Glu in the catalytic triad (DC-E), as well as that between the cyano group of nitrile substrates and Glu (DCN-E) were determined to coaffect the reaction pathway. A strategy of switching the characteristic distance “DC-E–DCN-E” of nitrilase was proposed to regulate its reaction specificity. By computer-aided in silico analysis and mutagenesis of hotspot residues, a triple mutant K200R/R224W/N246V and a hexamutant A87M/I91P/I136Q/M164V/R224S/V226R were obtained with strict hydrolysis and hydration activity, respectively. With phenylacetonitrile as a substrate, the content of phenylacetic acid produced by the triple mutant was increased from 50.9% to 98.5%, while that of phenylacetamide was increased from 49.1% to 96.4% by the hexamutant. The established computational design strategy provided important guidance to engineer nitrilases with inverse reaction specificity and meanwhile broadened their application fields.

Silver-modified zeolites exhibit high selectivity for alkene transformation to aromatic hydrocarbons. To inquire into the effect of silver cations in zeolite on the pathways of propene aromatization, the transformations of propene on H-ZSM-5 and Ag/H-ZSM-5 zeolites have been investigated by 13C MAS NMR and Fourier-transform infrared spectroscopy. It is established that propene transformation on H-ZSM-5 at 296–773 K occurs on Brønsted acid sites (BAS) by the mechanism of conjunct polymerization, as evidenced by the detection of cyclopentenyl cation intermediates. On the contrary, propene forms very stable π-complexes with Ag+ sites on Ag/H-ZSM-5, which prevents the alkene from converting on BAS at 296–623 K. At T ≥ 623 K, transformation proceeds with the assistance of silver cations via carbanionic allyl-like intermediate formation. Thus, the change in the reaction mechanism from conjunct polymerization on BAS to the mechanism with Ag+ ion involvement provides high selectivity for aromatic hydrocarbons on Ag+/H-ZSM-5 zeolite.

The complex and precise structure of natural monooxygenases makes it difficult to clone their structure and activity, and the reported artificial copper-based monooxygenase catalysts for the oxidation of inert C(sp3)–H bonds exhibit limited catalytic activities. Inspired by monooxygenases, we report a metal–organic framework (SiW12@CuMOF-1) comprising a binuclear copper HAT catalyst, photosensitizing nicotinamide adenine dinucleotide (NAD+) mimic bridging ligand, and embedded polyoxometalate. SiW12@CuMOF-1 accelerates the oxidative dehydrogenation of 3,5-DTBC with a catalytic efficiency comparable to that of natural polyphenol oxidase. In the presence of pyridine hydrochloride, irradiation of SiW12@CuMOF-1 afforded the highly active chlorine radical and CuI species via a ligand-to-metal charge transfer process. The chlorine radical abstracts a hydrogen atom selectively from C(sp3)–H bonds to generate the radical intermediate. The CuI species interacted with the active oxygen species 1O2 that formed from the photoinduced energy transfer from the excited state of the NAD+ mimics, giving the active oxygen species O2•– for further oxidization. The well-modified binuclear copper sites cleave the O–O bond to give the final products selectively. Meanwhile, the embedded polyoxometalates interacted with the alcohol substrates via hydrogen bonding interactions to help the catalytic conversion with high efficiency. The well-defined structural characters, the finely modified catalytic properties, and the sustainable multiphoton excitation photocatalytic processes provide a new avenue to develop robust artificial enzymes with uniform active sites and improved catalytic performances.

Solar hydrogen production by metal-free photocatalysts represents one of the important routes to realize a low-carbon energy system. Herein, the core–shell β-silicon carbide@potassium-doped polymeric carbon nitride (β-SiC@PPCN) heterojunction with β-SiC as a core and PPCN as a shell for photo-thermo catalytic hydrogen production is developed. With such a heterojunction, not only can the H–OH bond of absorbed water be activated, but also the migration of photogenerated carriers can be promoted due to the created internal-electric-field. Owing to the excellent photothermal conversion property of β-SiC, the temperature-dependent catalytic activity is also studied. The core–shell β-SiC@PPCN heterojunction can be run at an elevated temperature upon illumination, which enhances photoinduced electron–hole separation. Density functional theory calculations demonstrate that the elevated running temperature can activate absorbed water. Remarkably, the synergy of photocatalysis and thermocatalysis makes the core–shell β-SiC-50@PPCN heterojunction yield a photo-thermo catalytic hydrogen production rate as high as 13046.7 μmol·g–1·h–1. The present study provides a promising strategy for large-scale solar hydrogen production.