Oxygen vacancy induced superior catalytic performance in Nd-Ce confined inside carbon nanotubes for N2O-assisted dehydrogenation of ethylbenzene.

Binary Nd-Ce oxides encapsuled in carbon nanotubes (CNTs) catalysts were synthesized and evaluated in the coupling reaction of ethylbenzene (EB) dehydrogenation and N2O decomposition, a promising strategy for styrene (ST) production while mitigating greenhouse gas emissions. The optimized Nd - Ce@CNTs exhibited competitive catalytic performance with an EB conversion of 76 % and a ST selectivity of 71 % compared to Ce@CNTs, highlighting a synergic effect between Ce and Nd in the oxidation dehydrogenation of EB with N2O as an oxidant (N2O-ODEB). Characterization results indicated that Nd incorporation induced lattice distortions, evident in the expansion or contraction of Ce - O bonds surrounding Nd. Defect densities increased to 1.381, 1.495 and 1.534 for CNTs, Ce@CNTs, and Nd - Ce@CNTs, respectively. This interaction not only facilitated the generation of oxygen vacancies, with a lower formation energy of oxygen vacancy on Nd - Ce@CNTs (2.13 eV) than that on Ce@CNTs (2.49 eV), thereby enhancing oxygen activation and migration, but also optimized the distribution of acid sites, promoting CH activation and EB dehydrogenation. In - situ diffuse reflectance infrared Fourier-transform spectra (DRIFTS) and density functional theory (DFT) calculations revealed that the lower adsorption energy of N2O (-1.84 eV) on Nd - Ce@CNTs suggested a more favorable coordinated configuration than Ce@CNTs (-0.90 eV), supported by stronger adsorption intensities at 1270 cm-1 and 1302 cm-1. Furthermore, the elongated NO bond (1.35 Å) of N2O on the Nd - Ce@CNTs surface indicated its greater ease of cleavage, providing active oxygen species that collectively contributed to the enhanced catalytic performance in the N2O-ODEB.

Formic acid dehydrogenation using Ruthenium-POP pincer complexes in ionic liquids.

Formic acid is one of the most promising candidates for the long-term storage of hydrogen in liquid form. Herein, we present a new collection of ruthenium pincer complexes of the general formula [RuHCl(POP)(PPh3)] using commercially available or easy-to-synthesize tridentate xantphos-type POP pincer ligands. We applied these complexes in the dehydrogenation of formic acid to CO2 and H2 using the ionic liquid BMIM OAc (1-butyl-3-methylimidazolium acetate) as solvent under mild, reflux-free conditions. The best performing catalyst with respect to maximum turnover frequency, the literature-known complex [RuHCl(xantphos)(PPh3)] Ru-1, produced a maximum turnover frequency of 4525 h-1 with 74% conversion after 10 min at 90 °C and complete conversion (> 98%) occurring within 3 h. On the other hand, the best overall performing catalyst, the novel complex [RuHCl(iPr-dbfphos)(PPh3)] Ru-2, facilitated full conversion within 1 h leading to an overall turnover frequency of 1009 h-1. Moreover, catalytic activity was observed at temperatures as low as 60 °C. Only CO2 and H2 are observed in the gas phase, with no CO detected. High-resolution mass spectrometry suggests the presence of N-heterocyclic carbene complexes in the reaction mixture.

Progressive Fabrication of a Pt-Based High-Entropy-Alloy Catalyst toward Highly Efficient Propane Dehydrogenation.

High-entropy alloys (HEAs) have emerged as burgeoning heterogeneous catalysts due to their vast material space, unique structure, and superior stability. However, the dominant trial-and-error approaches hamper the exploration of efficient catalysts, necessitating the development of rational design strategies. Here, we report a progressive approach to the design and fabrication of HEA catalysts guided by alloying effects toward propane dehydrogenation. Cu, Sn, Au, and Pd are selected and demonstrated to induce dilution, encapsulation, surface enrichment, and inhomogeneity effects on Pt. The fabricated HEA, PtCuSnAuPd/SiO2, exhibits excellent activity, selectivity, and stability. The propylene formation rates reach 256 and 390 molC3H6 gPt-1 h-1 at 550 and 600 °C, respectively. Systematic characterizations reveal that the random elemental mixing, structural stability, and high Pt exposure promote the exposure of abundant stable isolated Pt sites. This work comprehensively explores the rational design and fabrication of HEA catalysts from a unique perspective, offering opportunities for developing advanced catalysts.

Sustainable Hydrogen Production by Glycerol and Monosaccharides Catalytic Acceptorless Dehydrogenation (AD) in Homogeneous Phase.

In the quest for sustainable hydrogen production, the use of biomass-derived feedstock is gaining importance. Acceptorless Dehydrogenation (AD) in the presence of efficient and selective catalysts has been explored worldwide as a suitable method to produce hydrogen from hydrogen-rich simple organic molecules. Among these, glycerol and sugars have the advantage of being cheap, abundant, and obtainable from fatty acid basic hydrolysis (biodiesel industry) and from biomass by biochemical and thermochemical processing, respectively. Although heterogeneous catalysts are more widely used for hydrogen production from biomass-based feedstock, the harsh reaction conditions applied limit applicability due to deactivation of active sites due to coking  of carbonaceous materials. Moreover, heterogeneous catalyst are more difficult to fine-tune than homogeneous counterparts, and the latter also allow for high process selectivities under milder conditions. The present Concept article summarizes the main features of the most active homogeneous catalysts reported for glycerol and monosaccharides AD. In order to directly compare  hydrogen production efficiencies, the choice of literature works was limited to reports where hydrogen was clearly quantified by yields and turnover numbers (TONs). The types of transition metals and ligands is discussed, together with a perspective view on future challenges of homogeneous AD reactions for practical applications.

Regulating Peripheral Nitrogen Dopants in Single-Atom Catalysts to Enhance Propane Dehydrogenation.

For single-atom catalysts (SACs), the dopants situated near the metal site have demonstrated a significant impact on the catalytic properties. However, the effect of dopants situated further away from the metal centers and their working mechanisms remain to be elucidated. Herein, we conduct density functional theory-driven studies on regulating the peripheral nitrogen dopants in graphene-based SACs, with a particular focus on Ir1 SAC, for propane dehydrogenation (PDH). It is found that increasing the distance between the N dopant and the Ir1 site results in a different energy change for the reaction process compared to the dense doping model with only first and second-shell N species. The proposed stochastic doping models demonstrate statistically that increasing the N dopant in farther shells not only enhances the activity of Ir1 but also maintains a high selectivity for propene, which is verified by experimental tests. The modulation of the d-band center of Ir1 by stochastic N dopants effectively modifies the binding strength of reaction intermediates, thereby enabling the optimization of the potential energy surface of PDH. These results deepen the understanding of dopant states around metal sites and provide an important implication for the doping engineering in heterogeneous catalysis.

Facile and Environmentally Friendly Synthesis of Ga2O3/MFI Catalysts for Propane Dehydrogenation.

A GaOx-based catalyst is recognized as a promising catalyst for dehydrogenation of light alkanes. Conventionally, impregnation and calcination are necessary processes for the loading of GaOx. However, the incomplete impregnation of gallium salt solution would generate wastewater, and the calcination for the dissociation of gallium salt would release harmful gases, such as SOx, NOx, and HCl. Meanwhile, the high temperature results in an excessive energy cost and undesired GaOx particle aggregation. Here, we report a facile and environmentally friendly method for the synthesis of GaOx-based catalysts. The gallium salt solution was replaced directly with liquid gallium (LG). Through a simple physical mixing method at room temperature, uniform GaOx nanoparticles with diameters of around 3.5 nm were loaded onto the surface of silicalite-1 (S-1). With the optimal GaOx/MFI catalyst, the propane conversion and propylene selectivity reached 22.9 and 90.1%, respectively, in the propane dehydrogenation reaction. The work offers a clean and economical strategy utilizing liquid metal (LM) as an impregnation solution for the preparation of GaOx-based catalysts.

Boosting Propane Dehydrogenation to Propylene via Electron Hole-Hydrogen Coupling on Cobalt Metal Surface.

Nonoxidative dehydrogenation of propane is useful for the high selectivity to propylene but is suffering from the heavy coke deposition on the catalyst surface. Herein, we present a proof-of-concept application of a hole-hydrogen (H) couple on a metallic cobalt surface to decrease the deactivation rate. The coupled H atoms on the Co surface, partially resulting from propane dehydrogenation, enabled the desorption of propylene to avoid deep hydrogenolysis and coke deposition and realize selective and durable propylene production, while conventional Co metal-based catalysts do not generate propylene. The optimized hole-H coupled Co catalyst provided a low deactivation rate (0.0036 h-1) and a high turnover frequency (55.6 h-1) for propylene production with a high propane flux (48 vol.% C3H8 in gas feeds) at 550 °C.

Metal-Organic Skeleton-Derived W-Doped Ga2O3-NC Catalysts for Aerobic Oxidative Dehydrogenation of N-Heterocycles.

N-heterocycles with quinoline structures hold significant importance within the chemical and pharmaceutical industries. However, achieving their efficient transformations remains a vital yet challenging endeavor. Herein, a series of W-doped Ga2O3-NC catalysts were synthesized using a Ga-MOF-derived strategy through a simple solvothermal method, with a remarkably high activity and selectivity towards the oxidative dehydrogenation of N-heterocycles. Furthermore, the MOF-derived W-doped Ga2O3-NC catalysts exhibit remarkable substrate tolerance and recyclability. The outstanding catalytic activity was attributed to the robust synergistic interaction between the W species and the Ga2O3-NC carrier, which facilitates the activation of hydrogen atoms in the C-H and C=N bonds on both the oxygen molecule and the substrate to produce H2O2. Additionally, the solvent effect of methanol can significantly enhance dehydrogenation due to its strong ability to donate and accept protons of hydrogen bonding. The present work provides a new approach to MOF-derived non-precious metal catalysts for achieving the efficient oxidation dehydrogenation of N-heterocycles.

Molten-salt-mediated Chemical Looping Oxidative Dehydrogenation of Ethane with In-situ Carbon Capture and Utilization.

The molten-salt-mediated oxidative dehydrogenation (MM-ODH) of ethane (C2H6) via a chemical looping scheme represents an effective carbon capture and utilization (CCU) method for the valorization of ethane-rich shale gas and concurrent mitigation of carbon dioxide (CO2) emissions. Here, stepwise experimentation with Li2CO3-Na2CO3-K2CO3 (LNK) ternary salts (i) assessed how each component of the LNK mixture impacted ethane MM-ODH performance and (ii) explored physicochemical and thermodynamic mechanisms behind melt-induced changes to ethylene (C2H4) and carbon monoxide (CO) yields. Of fifteen screened LNK compositions, nine exhibited ethylene yields greater than 50% at 800°C while maintaining C2H4 selectivities of 85% or higher. LNK salts rich in Li2CO3 content yielded more ethylene and CO on average than their counterparts, and net CO2 capture per cycle reached a maximum of ~75%. Extended MM-ODH cycling also demonstrated long-term stability of a high-performing LNK medium. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations suggested that the molten salt does not directly activate C2H6. Meanwhile, an empirical model informed by experimental data and reaction thermodynamics adequately predicted overall MM-ODH performance from LNK composition and provided insights into the system's primary drivers.

Liquid Organic Hydrogen Carrier Concepts and Catalysts for Hydrogenation and Dehydrogenation Reactions.

BACKGROUND: The issue of renewable energy (RE) source intermittency, such as wind and solar, along with the geographically uneven distribution of the global RE potential, makes it imperative to establish an energy transport medium to balance the energy demand and supply areas. A promising energy vector to address this situation is hydrogen, which is considered a clean energy carrier for various mobile and portable applications. Unfortunately, at standard pressure and temperature, its energy content per volume is very low (0.01 kJ/L). This necessitates alternative storage technologies to achieve reasonable capacities and enable economically viable long-distance transportation. Among the hydrogen storage technologies using chemical methods, liquid organic hydrogen carrier (LOHC) systems are considered a promising solution. They can be easily managed under ambient conditions, the H2 storage/release processes are carbon-free, and the carrier liquid is reusable. However, the evolution of the proposals from the carrier liquid type and catalyst elemental composition point of view is scarcely studied, considering that both are critical in the performance of the system (operational parameters, kinetic of the reactions, gravimetric hydrogen content, and others) and impact in the final cost of the technology deployed. The latter is due to the use of the Pt group elements (PGEs) in the catalyst that, for example, have a high demand in the hydrogen production sector, particularly for polymer electrolyte membrane (PEM) water electrolysis. With that in mind, our objective was to examine the evolution and the focus of the research in recent years related to proposals of LOHCs and catalysts for hydrogenation and dehydrogenation reactions in LOHC systems which can be useful in defining routes/strategies for new participants interested in becoming involved in the development of this technology. DATA SOURCES: For this systematic review, we searched the SCOPUS database and forward and backward citations for studies published in the database between January 2011 and December 2022. ELIGIBILITY CRITERIA: The criteria include articles which assessed or studied the effect of the type of catalyst, type of organic liquid, reactor design(s)/configuration(s), and modification of the reactor operational parameters, among others, over the performance of the LOHC system (de/hydrogenation reaction(s)). DATA EXTRACTION AND ANALYSIS: The relevant data from each reviewed study were collected and organized into a pre-designed table on an Excel spreadsheet, categorized by reference, year, carrier organic liquid, reaction (hydrogenation and/or dehydrogenation), investigated catalyst, and primary catalyst element. For processing the data obtained from the selected scientific publications, the data analysis software Orbit Intellixir was employed. RESULTS: For the study, 233 studies were included. For the liquid carrier side, benzyltoluene and carbazole dominate the research strategies. Meanwhile, platinum (Pt) and palladium (Pd) are the most employed catalysts for dehydrogenation reactions, while ruthenium (Ru) is preferred for hydrogenation reactions. CONCLUSIONS: From the investigated liquid carrier, those based on benzyltoluene and carbazole together account for over 50% of the total scientific publications. Proposals based on indole, biphenyl, cyclohexane, and cyclohexyl could be considered to be emerging within the time considered in this review, and, therefore, should be monitored for their evolution. A great activity was detected in the development of catalysts oriented toward the dehydrogenation reaction, because this reaction requires high temperatures and presents slow H2 release kinetics, conditioning the success of the implementation of the technology. Finally, from the perspective of the catalyst composition (monometallic and/or bimetallic), it was identified that, for the dehydrogenation reaction, the most used elements are platinum (Pt) and palladium (Pd), while, for the hydrogenation reaction, ruthenium (Ru) widely leads its use in the different catalyst designs. Therefore, the near-term initiatives driving progress in this field are expected to focus on the development of new or improved catalysts for the dehydrogenation reaction of organic liquids based on benzyltoluene and carbazole.

Unveiling the Potential of Heterogeneous Systems for Reversible Hydrogen Storage in Liquid Organic Hydrogen Carriers.

Transitioning towards a carbon-free economy is the current global need of the hour. The transportation sector is one of the major contributors of CO2 emissions in the atmosphere disturbing the delicate balance on the Earth, leading to global warming. Hydrogen has emerged as a promising alternative energy carrier capable of replacing fossil fuels, with advancements in systems facilitating its storage and long-distance transport. In this context, the concept of liquid organic hydrogen carriers (LOHCs) is taking the lead, offering a plausible solution because of its compatibility with the existing gasoline infrastructure, while eliminating the challenges associated with conventional hydrogen storage methods. Key LOHC systems, such as methylcyclohexane/toluene and H-18-dibenzyltoluene/dibenzyltoluene (H-18-DBT/DBT), have been extensively researched for large-scale applications. However, challenges persist, particularly concerning the endothermic nature of the reactions involved. In this regard, of particular interest are the multifunctional heterogeneous catalysts supported on a single support, offering cost-effective and energy-efficient solutions to circumvent issues related to the endothermicity of the reactions. In this review, solid heterogeneous catalysts that have been developed and investigated for reversible dehydrogenation and hydrogenation reactions have been presented. These catalysts include monometallic, bimetallic, and pincer complexes supported on materials designed for efficient hydrogen uptake and release.

Theoretical screening of single-atom catalysts (SACs) on Mo2TiC2O2 MXene for methane activation.

Producing value-added chemicals and fuels from methane (CH4) under mild conditions efficiently utilizes this cheap and abundant feedstock, promoting economic growth, energy security, and environmental sustainability. However, the first CH bond activation is a significant challenge and requires high energy. Efficient catalysts have been sought for utilizing CH4 at low temperatures including emerging single-atom catalysts (SACs). In this work, we screened fourteen transition metals (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Pt) doped at a single oxygen vacancy in Mo2TiC2O2 (TMSA-Mo2TiC2O2 SACs) for methane activation using density functional theory (DFT) calculations. Our results reveal that methane adsorption is thermodynamically stable on all simulated TMSA-Mo2TiC2O2 SACs, with the adsorption energies (Eads) ranging from -0.92 to -0.40 eV. For the CH activation process, Ru-SAC exhibits the lowest activation barrier (Ea) of 0.22 eV. In summary, Ru-, Rh-, Co-, V-, Cr-, Ti-, and Pt-SACs demonstrate promising catalytic properties for methane activation, with Ea values below 1.0 eV and an exothermic nature. Our findings pave the way for the design and development of novel single-atom catalysts in MXene materials, applicable not only for methane activation but also for other alkane dehydrogenation processes.

An Effective Strategy to Boost Formic Acid Dehydrogenation over Pd/AC-NH2 Catalyst through Pd Size Control.

Formic acid (FA, HCOOH) is regarded as one of the most promising carriers for hydrogen storage. However, the catalyst design for FA dehydrogenation into H2 with high efficiency is not clear. Here, we elucidate the rationale of size effect over the most commonly used Pd-based catalyst through supporting different Pd species, including single atoms, nanoclusters, and nanoparticles, on amine-functionalized active carbon (Pd/AC-NH2). The activity test presents that Pd/AC-NH2 with Pd nanoclusters exhibits the best turnover frequency (TOF) value of 40856 h-1 for 1 M FA at 328 K and even 1504 h-1 for neat FA at 308 K, which is comparable to the homogeneous catalysts and has been the first heterogeneous catalyst used in neat FA dehydrogenation under mild conditions. The comprehensive characterizations reveal that the size of Pd species affects the ratios of Pd0/Pd2+ and hydrogen spillover effect, which is crucial for the C-H cleavage and H2 desorption. Besides, the influences of amine groups on catalytic performance were further examined. This work provided an ingenious guideline to design efficient and practical catalysts for hydrogen storage under ambient conditions.

A density functional benchmark for dehydrogenation and dehalogenation reactions on coinage metal surfaces.

The on-surface synthesis of low-dimensional organic nanostructures has been extensively investigated through both experimental and theoretical methods, particularly by density functional theory (DFT). However, the complex mixture of interactions often poses challenges within the DFT framework, and there is a knowledge-gap regarding how the choice of DFT approach affects the computed results. Here, five different approaches including vdW interactions, i.e., PBE+D3, PBE+vdWsurf, rev-vdW-DF2, r2SCAN+rVV10 and BEEF-vdW, are employed to describe three prototypical on-surface reactions; dehydrogenation of benzene, debromination of bromobenzene, and deiodination of iodobenzene on the (111) facets of the coinage metals. Overall, rev-vdW-DF2 outperforms the other methods in describing benzene adsorption, whereas BEEF-vdW falls short. For dehydrogenation and debromination on Cu(111), all functionals except BEEF-vdW give reasonable activation energies compared to experiments. A similar trend is observed for Ag(111) and Au(111), with BEEF-vdW yielding significantly higher activation and reaction energies. For dehalogenation, all the five vdW approaches correctly capture the reactivity trend - Cu(111) > Ag(111) > Au(111) - and the expected hierarchy between bromobenzene desorption and carbon- bromine activation. Only BEEF-vdW fails to predict the faster kinetics of deiodination than the iodobenzene desorption. Our work forms a basis for evaluating density functionals in describing chemical reactions on surfaces.

Catalysts for Liquid Organic Hydrogen Carriers (LOHCs): Efficient Storage and Transport for Renewable Energy.

Restructuring the current energy industry towards sustainability requires transitioning from carbon based to renewable energy sources, reducing CO2 emissions. Hydrogen, is considered a significant clean energy carrier. However, it faces challenges in transportation and storage due to its high reactivity, flammability, and low density under ambient conditions. Liquid organic hydrogen carriers offer a solution for storing hydrogen because they allow for the economical and practical storage of organic compounds in regular vessels through hydrogenation and dehydrogenation. This review evaluates several hydrogen technologies aimed at addressing the challenges associated with hydrogen transportation and its economic viablity. The discussion delves into exploring the catalysts and their activity in the context of catalysts' development. This review highlights the pivotal role of various catalyst materials in enhancing the hydrogenation and dehydrogenation activities of multiple LOHC systems, including benzene/cyclohexane, toluene/methylcyclohexane (MCH), N-ethylcarbazole (NEC)/dodecahydro-N-ethylcarbazole (H12-NEC), and dibenzyltoluene (DBT)/perhydrodibenzyltoluene (H18-DBT). By exploring the catalytic properties of noble metals, transition metals, and multimetallic catalysts, the review provides valuable insights into their design and optimization. Also, the discussion revolved around the implementation of a hydrogen economy on a global scale, with a particular focus on the plans pertaining to Saudi Arabia and the GCC (Gulf Cooperation Council) countries. The review lays out the challenges this technology will face, including the need to increase its H2 capacity, reduce energy consumption by providing solutions, and guarantee the thermal stability of the materials.

An efficient electrode for reversible oxygen reduction/evolution and ethylene electro-production on protonic ceramic electrochemical cells.

Protonic ceramic electrochemical cells (PCECs) have demonstrated great promise for applications in the generation of electricity, and the synthesis of chemicals (for example, ethylene). However, enhancing the electrochemical reactions kinetics and stability of PCECs electrodes is one grand challenge. Here, we present a novel electrode material via a co-doping of cesium (Cs) and niobium (Nb) on PrBaCo2O6-δ with the composition of PrBa0.9Cs0.1Co1.9Nb0.1O6-δ (PBCCN), which naturally decomposes into dual phases of a double-perovskite PBCCN (DP-PBCCN, ∼92.3 wt%) and a single-perovskite Ba0.9Cs0.1Co0.95Nb0.05O3-δ (SP-BCCN, ∼7.7 wt%) under typical powder processing conditions. PBCCN exhibits a low area-specific resistance (ASR) value of 0.107 Ω cm2, an outstanding performance of 2.04 W cm-2 in fuel cell (FC) mode, a current density of -2.84 A cm-2 at 1.3 V in electrolysis cell (EC) mode, and promising reversible operational durability of 53 cycles in ∼212 h at +/- 0.5 A cm-2 and 650 °C. Cs doping generates more oxygen vacancies and accelerates the oxygen exchange kinetics, while Nb doping effectively enhances the stability, as illustrated by the analyses of X-ray photoelectron spectroscopy, and electrical conductivity relaxations. When applied as the positrode for electrochemical non-oxidative dehydrogenation of ethane (C2H6) to ethylene (C2H4) on PCECs, it displays an encouraging C2H6 conversion of 12.75% and a C2H4 selectivity of 98.4% at 1.2 V.

Recent Advances in Visible-Light-Driven Photocatalytic Oxidation Reactions in Water.

Oxidation reactions, which represent a fundamental process in organic transformations, have consistently advanced over several decades. Owing to the widespread application of aqueous and photochemical synthesis, research on light-induced oxidation in water, involving radical processes, has also experienced rapid development. Recently, numerous strategies for light-induced aqueous oxidation have been ingeniously designed and developed. This review aims to discuss the notable recent advancements in this rapidly evolving field of oxidation reactions, with a focus on delving into the reaction mechanisms. It hopes to inspire the development of aqueous photocatalytic oxidation reactions.

Boosting the Stability of Subnanometer Pt Catalysts by the Presence of Framework Indium(III) Sites in Zeolite.

Subnanometer metal clusters show advantages over conventional metal nanoparticles in numerous catalytic reactions owing to their high percentage of exposed surface sites, abundance of under-coordinated metal sites and unique electronic structures. However, the applications of subnanometer metal clusters in high-temperature catalytic reactions (>600 °C) are still hindered, because of their low stability under harsh reaction conditions. In this work, we have developed a zeolite-confined bimetallic PtIn catalyst with exceptionally high stability against sintering. A combination of experimental and theoretical studies shows that the isolated framework In(III) species serve as the anchoring sites for Pt species, precluding the migration and sintering of Pt species in the oxidative atmosphere at ≥650 °C. The catalyst comprising subnanometer PtIn clusters exhibits long-term stability of >1000 h during a cyclic reaction-regeneration test for ethane dehydrogenation reaction.

Recent Advances and Insights in Designing ZnxCd1-xS-Based Photocatalysts for Hydrogen Production and Synergistic Selective Oxidation to Value-Added Chemical Production.

Combining the hydrogen (H2) extraction process and organic oxidation synthesis in photooxidation-reduction reactions mediated by semiconductors is a desirable strategy because rich chemicals are evolved as byproducts along with hydrogen in trifling conditions upon irradiation, which is the only effort. The bifunctional photocatalytic strategy facilitates the feasible formation of a C═O/C─C bond from a large number of compounds containing a X-H (X = C, O) bond; therefore, the production of H2 can be easily realized without support from third agents like chemical substances, thus providing an eco-friendly and appealing organic synthesis strategy. Among the widely studied semiconductor nanomaterials, ZnxCd1-xS has been continuously studied and explored by researchers over the years, and it has attracted much consideration owing to its unique advantages such as adjustable band edge position, rich elemental composition, excellent photoelectric properties, and ability to respond to visible light. Therefore, nanostructures based on ZnxCd1-xS have been widely studied as a feasible way to efficiently prepare hydrogen energy and selectively oxidize it into high-value fine chemicals. In this Review, first, the crystal and energy band structures of ZnxCd1-xS, the model of twin nanocrystals, the photogenerated charge separation mechanism of the ZB-WZ-ZB homojunction with crisscross bands, and the Volmer-Weber growth mechanism of ZnxCd1-xS are described. Second, the morphology, structure, modification, synthesis, and vacancy engineering of ZnxCd1-xS are surveyed, summarized, and discussed. Then, the research progress in ZnxCd1-xS-based photocatalysis in photocatalytic hydrogen extraction (PHE) technology, the mechanism of PHE, organic substance (benzyl alcohol, methanol, etc.) dehydrogenation, the factors affecting the efficiency of photocatalytic discerning oxidation of organic derivatives, and selective C-H activation and C-C coupling for synergistic efficient dehydrogenation of photocatalysts are described. Conclusively, the challenges in the applicability of ZnxCd1-xS-based photocatalysts are addressed for further research development along this line.

Highly Stable Propane Dehydrogenation on a Self-Supporting Single-Component Zn2SiO4 Catalyst.

Current industrial propane dehydrogenation (PDH) processes predominantly use either toxic Cr-based or expensive Pt-based catalysts, necessitating urgent exploration for alternatives. Herein, we present Zn2SiO4, an easily prepared, cost-effective material, as a highly efficient and stable catalyst for PDH. Uniquely, Zn2SiO4 nanocrystals do not require dispersion on support materials, commonly needed for catalytic active oxide clusters, but function as a self-supporting catalyst instead. During the reaction's induction period, surface Zn species on the Zn2SiO4 crystal reduce to coordinately unsaturated ZnOx single sites, serving as highly active catalytic centers. The Zn2SiO4 catalyst demonstrates a stable performance over 200 hours of PDH operation at 550 °C. We further find that introducing a minuscule amount of CO2 into the propane feed significantly extends the catalyst lifespan to over 2000 hours. This enhancement arises from the special role of CO2 in facilitating the removal of strongly adsorbed H*, preventing the complete reduction of ZnOx. After prolonged reaction, the activity of Zn2SiO4 can be fully restored by etching the surface layer to expose fresh Zn species, available throughout the crystals. The combination of CO2introduction and catalytic site regeneration strategies is expected to enable a year-long PDH operation using a single batch of Zn2SiO4 catalyst.