Steam-Assisted Selective CO2 Hydrogenation to Ethanol over Ru-In Catalysts.

Multicomponent catalysts can be designed to synergistically combine reaction intermediates at interfacial active sites, but restructuring makes systematic control and understanding of such dynamics challenging. We here unveil how reducibility and mobility of indium oxide species in Ru-based catalysts crucially control the direct, selective conversion of CO2 to ethanol. When uncontrolled, reduced indium oxide species occupy the Ru surface, leading to deactivation. With the addition of steam as a mild oxidant and using porous polymer layers to control In mobility, Ru-In2O3 interface sites are stabilized, and ethanol can be produced with superior overall selectivity (70%, rest CO). Our work highlights how engineering of bifunctional active ensembles enables cooperativity and synergy at tailored interfaces, which unlocks unprecedented performance in heterogeneous catalysts.

Highly Dispersed Pd-CeOx Nanoparticles in Zeolite Nanosheets for Efficient CO2-Mediated Hydrogen Storage and Release.

Formic acid (FA) dehydrogenation and CO2 hydrogenation to FA/formate represent promising methodologies for the efficient and clean storage and release of hydrogen, forming a CO2-neutral energy cycle. Here, we report the synthesis of highly dispersed and stable bimetallic Pd-based nanoparticles, immobilized on self-pillared silicalite-1 (SP-S-1) zeolite nanosheets using an incipient wetness co-impregnation technique. Owing to the highly accessible active sites, effective mass transfer, exceptional hydrophilicity, and the synergistic effect of the bimetallic species, the optimized PdCe0.2/SP-S-1 catalyst demonstrated unparalleled catalytic performance in both FA dehydrogenation and CO2 hydrogenation to formate. Remarkably, it achieved a hydrogen generation rate of 5974 molH2 molPd-1 h-1 and a formate production rate of 536 molformate molPd-1 h-1 at 50 °C, surpassing most previously reported heterogeneous catalysts under similar conditions. Density functional theory calculations reveal that the interfacial effect between Pd and cerium oxide clusters substantially reduces the activation barriers for both reactions, thereby increasing the catalytic performance. Our research not only showcases a compelling application of zeolite nanosheet-supported bimetallic nanocatalysts in CO2-mediated hydrogen storage and release but also contributes valuable insights towards the development of safe, efficient, and sustainable hydrogen technologies.

One-pot conversion of xylose to 1,2-pentanediol catalyzed by an organic acid-assisted Pt/NC in aqueous phase.

The direct synthesis of 1,2-pentanediol (1,2-PeD) from renewable xylose and its derivatives derived from hemicellulose is appealing yet challenging due to its low selectivity for the target product. In this study, one-pot catalytic conversion of xylose to 1,2-PeD was performed by using nitrogen-doped carbon (NC) supported Pt catalysts with the assistance of organic acids. A remarkable yield of 49.3% for 1,2-PeD was achieved by reacting 0.1869 g xylose in 30 mL water at 200 °C under a hydrogen pressure of 3 MPa for 8 h in the presence of 0.1 g of 2.5Pt/NC600 catalyst and 0.1869 g propanoic acid co-catalyst. The presence of vicinal Pt-acid pair sites on the surface of the 2.5Pt/NC600 catalyst exhibited a synergistic effect in promoting the hydrogenation of furfural to furfuryl alcohol intermediate and subsequent hydrogenation and ring-opening reactions leading to the formation of 1,2-PeD. The addition of organic acids, may serve as both acid catalyst for dehydration of xylose and hydrogen donor for hydrogenation of furfural and furfuryl alcohol, thereby promoting the one-pot conversion of xylose to 1,2-PeD. Remarkably, the 2.5Pt/NC600 catalyst demonstrated outstanding catalytic performance and good reusability over five consecutive cycles without significant deactivation.

Applications of Ene-Reductases in the Synthesis of Flavors and Fragrances.

Flavors and fragrances (F&F) are interesting organic compounds in chemistry. These compounds are widely used in the food, cosmetic, and medical industries. Enzymatic synthesis exhibits several advantages over natural extraction and chemical preparation, including a high yield, stable quality, mildness, and environmental friendliness. To date, many oxidoreductases and hydrolases have been used to biosynthesize F&F. Ene-reductases (ERs) are a class of biocatalysts that can catalyze the asymmetric reduction of α,ß-unsaturated compounds and offer superior specificity and selectivity; therefore, ERs have been increasingly considered an ideal alternative to their chemical counterparts. This review summarizes the research progress on the use of ERs in F&F synthesis over the past 20 years, including the achievements of various scholars, the differences and similarities among the findings, and the discussions of future research trends related to ERs. We hope this review can inspire researchers to promote the development of biotechnology in the F&F industry.

Pnictogen-Bonding Enzymes.

The objective of this study was to create artificial enzymes that capitalize on pnictogen bonding, a s-hole interaction that is essentially absent in biocatalysis.  For this purpose, stibine catalysts were equipped with a biotin derivative and combined with streptavidin mutants to identify an efficient transfer hydrogenation catalyst for the reduction of a fluorogenic quinoline substrate.  Increased catalytic activity from wild-type streptavidin to the best mutants coincides with the depth of the s hole on the Sb(V) center, and the emergence of saturation kinetic behavior.  Michaelis-Menten analysis reveals transition-state recognition in the low micromolar range, more than three orders of magnitude stronger than the millimolar substrate recognition.  Carboxylates preferred by the best mutants contribute to transition-state recognition by hydrogen-bonded ion pairing and anion-π interactions with the emerging pyridinium product.  The emergence of challenging stereoselectivity in aqueous systems further emphasizes compatibility of pnictogen bonding with higher order systems catalysis.

Embedding Single Pd Atoms on NiGa Intermetallic Surfaces for Efficient and Selective Alkyne Semi-hydrogenation.

Catalytic removal of alkynes is essential in industry for producing polymer-grade alkenes from steam cracking processes. Non-noble Ni-based catalysts hold promise as effective alternatives to industrial Pd-based catalysts but suffer from low activity. Here we report embedding of single-atom Pd onto the NiGa intermetallic surface with replacing Ga atoms via a well-defined synthesis strategy to design Pd1-NiGa catalyst for alkyne semi-hydrogenation. The fabricated Pd1Ni2Ga1 ensemble sites deliver remarkably higher specific mass activity under superb alkene selectivity of >96% than the state-of-the-art catalysts under industry-relevant conditions. Integrated experimental and computational studies reveal that the single-atom Pd located synergizes with the neighbouring Ni sites to facilitate the σ-adsorption of alkyne and dissociation of hydrogen while suppress the alkene adsorption. Such synergistic effects confer the single-atom Pd on the NiGa intermetallic with a Midas touch for alkyne semi-hydrogenation, providing an effective strategy for stimulating low active Ni-based catalysts for other selective hydrogenations in industry.

Lewis Acid-Tethered (cAAC)-Copper Complexes: Reactivity for Hydride Transfer and Catalytic CO2 Hydrogenation.

We present a series of borane-tethered cyclic (alkyl)(amino)carbene (cAAC)-copper complexes, including a borane-capped Cu(I) hydride. This hydride is unusually hydridic and reacts rapidly with both CO2 and 2,6-dimethylphenol at room temperature. Its reactivity is distinct from variants without a tethered borane, and the underlying principles governing the enhanced hydricity were evaluated experimentally and theoretically. These stoichiometric results were extended to catalytic CO2 hydrogenation, and the borane-tethered (intramolecular) system exhibits ~3-fold enhancement relative to an intermolecular system.

Hydrogen Spillover Mechanism at the Metal-Metal Interface in Electrocatalytic Hydrogenation.

Hydrogen spillover in metal-supported catalysts can largely enhance electrocatalytic hydrogenation performance and reduce energy consumption. However, its fundamental mechanism, especially at the metal-metal interface, remains further explored, impeding relevant catalyst design. Here, we theoretically profile that a large free energy difference in hydrogen adsorption on two different metals (|ΔGH-metal(i) - ΔGH-metal(ii)|) induces a high kinetic barrier to hydrogen spillover between the metals. Minimizing the difference in their d-band centers (Δεd) should reduce |ΔGH-metal(i) - ΔGH-metal(ii)|, lowering the kinetic barrier to hydrogen spillover for improved electrocatalytic hydrogenation. We demonstrated this concept using copper-supported ruthenium-platinum alloys with the smallest Δεd, which delivered record high electrocatalytic nitrate hydrogenation performance, with ammonia production rate of 3.45±0.12 mmol h-1 cm-2 and Faraday efficiency of 99.8±0.2 %, at low energy consumption of 21.4 kWh kgamm-1. Using these catalysts, we further achieve continuous ammonia and formic acid production with a record high-profit space.

Tailoring Catalysis of Encapsulated Pt Nanoparticles by Pore Wall Engineering of Covalent Organic Frameworks.

While supported metal nanoparticles (NPs) have shown significant promise in heterogeneous catalysis, precise control over their interaction with the support, which profoundly impacts their catalytic performance, remains a significant challenge. In this study, Pt NPs are incorporated into thioether-functionalized covalent organic frameworks (denoted COF-Sx), enabling precise control over the size and electronic state of Pt NPs by adjusting the thioether density dangling on the COF pore walls. Notably, the resulting Pt@COF-Sx demonstrate exceptional selectivity (>99%) in catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline, in sharp contrast to the poor selectivity of Pt NPs embedded in thioether-free COFs. Furthermore, the conversion over Pt@COF-Sx exhibits a volcano-type curve as the thioether density increases, due to the corresponding change of accessible Pt sites. This work provides an effective approach to regulating the catalysis of metal NPs via their microenvironment modulation, with the aid of rational design and precise tailoring of support structure.

How the addition of atomic hydrogen to a multiple bond can be catalyzed by water molecules.

Observational data show complex organic molecules in the interstellar medium (ISM). Hydrogenation of small unsaturated carbon double bond could be one way for molecular complexification. It is important to understand how such reactivity occurs in the very cold and low-pressure ISM. Yet, there is water ice in the ISM, either as grain or as mantle around grains. Therefore, the addition of atomic hydrogen on double-bonded carbon in a series of seven molecules have been studied and it was found that water catalyzes this reaction. The origin of the catalysis is a weak charge transfer between the π MO of the unsaturated molecule and H atom, allowing a stabilizing interaction with H2O. This mechanism is rationalized using the non-covalent interaction and the quantum theory of atoms in molecules approaches.

Hydrogenation of the benzene rings in PET degraded chemicals over meso-HZSM-5 supported Ru catalyst.

Chemical upcycling of waste polyethylene terephthalate (PET) to value-added products can reduce the emission of CO2, microplastics and toxic chemicals. In this work, mesoporous H-type Zeolite Socony Mobil-5 (HZSM-5) supported Ru catalyst (Ru/m-HZSM-5) was synthesized and tested in the hydrogenation of PET degraded chemicals (bis(2-hydroxyethyl) terephthalate, dimethyl terephthalate, diethyl terephthalate, and terephthalic acid). Characterizations disclosed that Ru/m-HZSM-5 catalyst possesses mesopores (a dominant channel of 5.32 nm), enlarged specific surface area (404 m2·g-1), and Ru NPs dispersed highly (40.6 %) compared to that of Ru/HZSM-5. And also, it was found that Ru/m-HZSM-5 was capable for the hydrogenation of benzene rings in these PET degraded chemicals with large sizes (1.09-1.82 nm). In particular, the conversion of BHET and the selectivity of BHCD over Ru/m-HZSM-5 reached 95.5 % and 95.6 % at 120 °C within 2 h. And Ru/m-HZSM-5 could be recycled at least five times without obvious loss of activity and selectivity.

Bridging dehydrogenation and hydrogenation in heterogeneous catalysis: A demonstration of a unified catalytic approach.

In the pursuit of enhancing the applications of hydrogen as an energy carrier, this research delved into the utilization of a singular hybrid catalyst capable of performing both dehydrogenation and hydrogenation processes for Liquid Organic Hydrogen Carriers (LOHCs). This study presents the synthesis and characterization of a hybrid catalyst, combining an organometallic pincer complex with Pd-Ru heterostructures supported on γ-alumina. Unlike conventional transition and noble metal nanoparticles, the use of a pincer complex offers exceptional thermal stability due to its aryl backbone, which is advantageous for various endothermic dehydrogenation reactions of hydrocarbons in LOHCs. This pioneering hybrid catalyst is a novel approach, demonstrating a proof of concept. In this study, we utilized the hybrid catalyst to investigate the dehydrogenation and hydrogenation of a lower enthalpic system, specifically the cyclooctane-cyclooctene system. The dehydrogenation of cyclooctane was conducted at 443 K using tertiary butyl ethylene as a sacrificial hydrogen acceptor, while the hydrogenation of cyclooctene reaction catalyzed by Pd-Ru nanostructures occurred at 298 K and 1 atm H2. The results showed successful tandem dehydrogenation-hydrogenation reactions. However, challenges were noted in terms of catalytic activity and recyclability, providing valuable insights for further refinement and optimization.

Thermally Stable P-Chiral Supramolecular Phosphines, their Self-Assembly and Implication in Rh-Catalyzed Asymmetric Hydrogenation.

P-chiral supramolecular phosphine ligands are crucial for asymmetric transformations, but their synthesis is tedious. We report a one-step synthesis of thermally stable P-chiral supramolecular phosphines and their performance in the asymmetric hydrogenation of functionalized alkenes. A rational designing and synthesis of (R, R)-QuinoxP* ligated palladium complex (Pd-2) in excellent yield is reported. This Pd-2 catalyzed a direct P-C coupling of 2,3-dihydro-1-H-phosphindole (A1)/1,2,3,4-tetrahydrophosphindoline (A2) with 1-(3-iodophenyl)urea/2-iodo (B1)/6-hydroxy pyridine (B2) and, produced corresponding ligands L1-L3. The P-C coupling between A1 and B2 produced 6-(2,3-dihydro-1H-phosphindol-1-yl)pyridine-2(1H)-one (L2) with an excellent enantiomeric excess of up to 99%. L2 was found to be remarkably stable even at 150 °C and did not oxidize/hydrolyze for at least 24 hours in open air. Such thermal stability and an impediment to oxidation are unprecedented. L2 self-assembled and produced L2-C1 (Pt), L2-C2(Pd), and L2-C3(Rh) assemblies. The utility of the self-assembled P-chiral ligand was demonstrated in the Rh-catalyzed asymmetric hydrogenation (AH) of functionalized olefins. The L2-C3 catalyzed AH of functionalized alkenes and delivered chiral products with excellent enantioselectivity of >99%. A small library of 16 substrates was subjected to AH using L2-C3 to produce chiral compounds with excellent conversion and ee.

Green synthesis of silver nanoparticles-capped aminated lignin as a robust active catalyst for dye discoloration.

Considering the severity of global environmental issues, biomass-derived products have received significant attention as alternatives to foster sustainability and eco-friendliness. The use of metal nanoparticle catalysts for dye decomposition is emerging as a promising approach for environmentally friendly dye removal. In this study, an aminosilane-modified lignin (AML)/silver nanoparticle (AgNP) composite was fabricated and used as a hydrogenation catalyst. The AgNPs were well dispersed on the AML surface and formed strong bonds within the AML/AgNP complex. AML also served as an effective reducing and capping agent for Ag(I) ions. The AML/AgNPs were found to be an efficient catalyst with excellent dye degradation ability and easy reusability. Biomass-derived lignin can be used as a reducing and capping agent for metals and this complex can be used as a high-value bio-catalyst for wastewater remediation.

In-Situ Characterization Techniques for Mechanism Studies of CO2 Hydrogenation.

The paramount concerns of global warming, fossil fuel depletion, and energy crises have prompted the need of hydrocarbons productions via CO2 conversion. In order to achieve global carbon neutrality, much attention needs to be diverted towards CO2 management. Catalytic hydrogenation of CO2 is an exciting opportunity to curb the increasing CO2 and produce value-added products. However, the comprehensive understanding of CO2 hydrogenation is still a matter of discussion due to its complex reaction mechanism and involvement of various species. This review comprehensively discusses three processes: reverse water gas shift (RWGS) reaction, modified Fischer Tropsch synthesis (MFTS), and methanol-mediated route (MeOH) for CO2 hydrogenation to hydrocarbons. It is also very important to understand the real-time evolvement of catalytic process and reaction intermediates by employing in-situ characterization techniques. Subsequently, in second part of this review, we provided a systematic analysis of advancements in in-situ techniques aimed to monitor the evolution of catalysts during CO2 reduction process. The section also highlights the key components of in-situ cells, their working principles, and applications in identifying reaction mechanisms for CO2 hydrogenation. Finally, by reviewing respective achievements in the field, we identify key gaps and present some future directions for CO2 hydrogenation and in-situ studies.

Carbon dioxide conversion to fuel over alumina-supported ruthenium catalysts.

In this study, ruthenium-based catalysts were prepared for CO2 hydrogenation. Incipient-wetness-impregnation of the alumina-support with ruthenium (III) nitrosyl nitrate solution to achieve 0.5 wt% Ru loading on supports was used to prepare these catalysts. Potassium (0-3 % wt%) was used to further promote the catalysts. TPR, CO2-TPD, XRD, TEM, XPS, SEM, and EDS analyses were used to characterize catalyst properties. The hydrogenation of CO2 catalytic tests were conducted and the effect of operating conditions (temperature, pressure, and space velocity) were investigated. These studies were conducted in a tubular fixed-bed reactor. The CO2 conversion over these catalysts was found to be low and the dominating product observed was CH4 with a small amount of C2+ forming when K was added to the catalyst. The optimum potassium loading for improved C2+ product yield over Ru/Al2O3 was 1%K for CO2 hydrogenation.

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis.

Nanoparticle (NP) size and proximity are two physical descriptors applicable to practically all NP-supported catalysts. However, with conventional catalyst design, independent variation of these descriptors to investigate their individual effects on thermocatalysis remains challenging. Using a raspberry-colloid-templating approach, we synthesized a well-defined catalyst series comprising Pd12Au88 alloy NPs of three distinct sizes and at two different interparticle distances. We show that NP size and interparticle distance independently control activity and selectivity, respectively, in the hydrogenation of benzaldehyde to benzyl alcohol and toluene. Surface-sensitive spectroscopic analysis indicates that the surfaces of smaller NPs expose a greater fraction of reactive Pd dimers, compared to inactive Pd single atoms, thereby increasing intrinsic catalytic activity. Computational simulations reveal how a larger interparticle distance improves catalytic selectivity by diminishing the local benzyl alcohol concentration profile between NPs, thus suppressing its readsorption and consequently, undesired formation of toluene. Accordingly, benzyl alcohol yield is maximized using catalysts with smaller NPs separated by larger interparticle distances, overcoming activity-selectivity trade-offs. This work exemplifies the high suitability of the modular raspberry-colloid-templating method as a model catalyst platform to isolate individual descriptors and establish clear structure-property relationships, thereby bridging the materials gap between surface science and technical catalysts.

Expedited Synthesis of Metal Phosphides Maximizes Dispersion, Air Stability, and Catalytic Performance in Selective Hydrogenation.

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation substantially lower the appeal and performance of metal phosphides in catalysis. We show here that a 1-step procedure that relies on safe and cheap precursors can furnish an air-stable Ni2P/Al2O3 catalyst containing 3.2 nm nanoparticles. Ni2P/Al2O3 1-step is kinetically competitive with the palladium-based Lindlar catalyst in selective hydrogenation catalysis, and a loading corresponding to 4 ppm Ni was sufficient to convert 0.1 mol alkyne. The 1-step synthetic procedure alters the surface ligand speciation of Ni2P/Al2O3, which protects the nanoparticle surface from oxidation, and ensures that 85 % of the initial catalytic activity was retained after the catalyst was stored under air for 1.5 years. Preparation of Ni2P on a variety of supports (silica, TiO2, SBA-15, ZrO2, C and HAP) as well as Co2P/Al2O3, Co2P/TiO2 and bimetallic NiCoP/TiO2 demonstrates the generality with which supported metal phosphides can be accessed in a safe and straightforward fashion with small sizes and high dispersion.

Implications for the Hydrogenation of Propyne and Propene with Parahydrogen due to the in†situ Transformation of Rh2C to Rh0/C.

NMR spectroscopy studies using parahydrogen-induced polarization have previously established the existence of the pairwise hydrogen addition route in the hydrogenation of unsaturated hydrocarbons over heterogeneous catalysts, including those based on rhodium (Rh0). This pathway requires the incorporation of both hydrogen atoms from one hydrogen molecule to the same product molecule. However, the underlying mechanism for such pairwise hydrogen addition must be better understood. The involvement of carbon, either in the form of carbonaceous deposits on the surface of a catalyst or as a metal carbide phase, is known to modify catalytic properties significantly and thus could also affect the pairwise hydrogen addition route. Here, we explored carbon's role by studying the hydrogenation of propene and propyne with parahydrogen on a Rh2C catalyst and comparing the results with those for a Rh0/C catalyst obtained from Rh2C via H2 pretreatment. While the catalysts Rh2C and Rh0/C differ notably in the rate of conversion of parahydrogen to normal hydrogen as well as in terms of hydrogenation activity, our findings suggest that the carbide phase does not play a significant role in the pairwise H2 addition route on rhodium catalysts.

A composite of AgNPs and lignin porous microspheres via in-situ reduction of Ag+ and its catalytic performance.

Despite the widespread utilization of nano silver composites in the domain of catalytic hydrogenation of aromatic pollutants in wastewater, certain challenges persist, including the excessive consumption of chemical reagents during the preparation process and the difficulty in recycling. In this study, silver ions were reduced in-situ by taking advantage of the adsorptive and reducing capacities of hydroxyls and amino groups on lignin porous microspheres (LPMs) under mild ultrasonic conditions, and lignin porous microspheres loaded with silver nanoparticles (Ag@LPMs) were conveniently prepared. Ag@LPMs had excellent catalytic and cycling performances for p-nitrophenol (4-NP), methylene blue (MB) and methyl orange (MO). The 4-NP could be completely reduced to 4-AP within 155 s under the catalysis of Ag@LPMs, with a pseudo-first-order kinetic constant of 1.28 min-1. Furthermore, Ag@LPMs could still complete the catalytic reduction of 4-NP within 10 min after five cycles. Ag@LPMs with the particle size ranging from 100 to 200 µm conferred ease of recycling, and the porous structure effectively resolved the issue of sluggish mass transfer encountered during the catalytic process. At the same time, the binding force of nano silver and LPMs obtained by ultrasonic was stronger than that of heating, so the materials prepared by ultrasonic had better cycling performance. Silver ions concentration and pH value in the preparation process affected the catalytic performance of Ag@LPMs, 50 mmol/L Ag+ and pH value of 7 turned out to be the optimization conditions.