Journal of Catalysis最新文献

A novel mesoporous SiO₂ encapsulated core-shell NiRh@NiO nanostructure was constructed to enhance the activity and stability of ethanol steam reforming (ESR). At 550 °C and ethanol-WHSV = 21 h⁻¹, the specific activity and conversion loss (17 h) of NiRh@NiO@m-SiO₂ were 0.42 mol_ethanol/(g_cat.·h) and 10.9 %. The alloying of NiRh core, dominated NiO in shell, and abundant mesopore of SiO₂ were confirmed by systematic characterization techniques. The in situ DRIFTS results indicated that alloying Ni and Rh boosted ethoxide dehydrogenation to acetaldehyde and acetate demethanation to carbonate. ReaxFF molecular dynamics (MD) simulations suggested that NiO shell was conducive to water activation, which, in turn, promoted the conversion of CH_xO_y species. The SiO₂ encapsulation derived confinement effect inhibited both metal core sintering and leaching caused by the filamentous carbon. The abundant mesopores of SiO₂ ensured the facile in-diffusion of water and out-diffusion of carbonaceous products, suppressing carbon deposition within the SiO₂ encapsulation and the destruction of core-shell structure.

The defect chemistry of doped-ceria is vital but tangled for sustainable conversion of biomass resources. In this work, a group of Zr-doped CeO₂ solid solutions were prepared and the defect chemistry in CeZr_xO_y (0.02 ≤ x ≤ 5) catalyst was elucidated over the oxidative coupling of lignin-based aniline and benzyl alcohol. Varying the Zr molar fraction enabled to successfully adjust the defect sites of catalysts and further influence their catalytic performances. In addition, the optimal CeZr₁O_y catalyst exhibited a flexible temperature adaptability, wide substrate scope and superior reusability. Various characterizations, kinetic investigations, controlled experiments, DFT calculations and in situ DRIFT-IR technique were used to unravel the roles of Ce³⁺ and oxygen defects and the reaction mechanism. It was disclosed that Zr-doped defects can obviously increase surface Ce³⁺ cations, oxygen species (peroxide and superoxide anions) and oxygen vacancies. These coordinatively unsaturated sites were shown to play critical roles in absorbing and activating substrates hence can accelerate the formation rate of bio-based imines.

CO₂ methanation at low temperatures is still a challenge. Herein, Ni_nCeO_x (n = 1–3) and Ni_2.5Pd_0.1CeO_x nanofibers by electrospinning is reported. The main advantage of this method is to obtain the highly dispersed precursor of palladium, nickel, and cerium, overcoming the difficulty of uniform mixing in conventional preparation methods. The Ni_2.5Pd_0.1CeO_x nanofiber catalyst exhibited outstanding catalytic performance at low temperatures (CO₂ conversion rate = 90.4 %, CH₄ selectivity = 99.6 % at 230 °C) along with exceptional stability over 300 h. EPR, Raman, and O 1s XPS confirmed that Pd²⁺ doping increased oxygen vacancy concentration. In-situ infrared spectroscopy indicated that CO₂ methanation on Ni_2.5CeO_x and Ni_2.5Pd_0.1CeO_x catalysts followed the formate pathways. Pd²⁺ doping increased the number of surface oxygen vacancies and hydroxyl groups, thus increasing the amount of bicarbonates and formates. DFT calculations suggested that Pd²⁺ doping increased CO₂ adsorption energy, and confirmed surface hydroxyl groups and bicarbonate being beneficial for CO₂ methanation, consequently enhancing the activity of Ni_2.5Pd_0.1CeO_x catalyst especially at low temperatures.

Photoelectrochemical (PEC) water splitting provides a potential method to produce renewable hydrogen energy, but there is still plenty of room for improving the efficiency and stability of photoelectrodes. In this paper, we present a metal–insulator-semiconductor (MIS) structure based on p-Si that enables stable and efficient water splitting by engineering the interfacial insulating layer. The silicon oxide (SiO_x) film with appropriate thickness and low defects is regrown by a chemical oxidation process, which provides a high-quality insulating layer to passivate the p-Si. The carrier flux, barrier height and interfacial resistance of p-Si based MIS junction can be systematically tuned by controlling the thickness and quality of SiO_x layer. Under AM 1.5G illumination, the optimized p-Si/SiO_x/Ti/Pt photoelectrode shows an onset potential of 0.5 V vs. RHE, a maximum photocurrent of 28 mA/cm² and a high applied bias photon-to-current efficiency (ABPE) of 6 %. These results have significant implications for constructing MIS photoelectrodes towards effective water splitting.

Rational design and engineering of cost-effective, high-performance reversible oxygen electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is imperative in advancing the progress of rechargeable metal-air batteries (r-MABs). Herein, nanocomposites based on Co@Ru core@shell nanoparticles embedded within N-doped carbon nanosheets (Co@Ru/CS) are prepared via facile galvanic exchange reactions of RuCl₃ with Co/NC and used as an effective oxygen electrocatalyst for rechargeable zinc-air battery (r-ZAB). Electrochemical studies demonstrate a remarkable bifunctional catalytic performance of Co@Ru/CS towards both ORR and OER, featuring a low potential gap (ΔE) of only 0.69 V between the OER potential (E_10,OER) at 10 mA cm⁻² and half-wave potential (E_1/2,ORR) of ORR, which is much lower than that of commercial Pt/C + RuO₂ catalysts (0.76 V). Combined studies of experimental characterizations and density functional theory calculations show that the ORR activity arises primarily from the N-doped carbon and CoN_x moieties in the composites, whereas RuO₂/CoOOH produced at high electrode potentials is responsible for the OER activity. Co@Ru/CS based r-ZAB exhibits an open circuit voltage of 1.447 V, specific capacity of 781 mAh g_Zn⁻¹, and maximum power density of 115 mW cm⁻² at 0.83 V, a performance better than that with commercial Pt/C + RuO₂ (1.412 V, 760.56 mAh g_Zn⁻¹, and 91 mW cm⁻²). Results from this research underline the substantial impact of structural engineering on optimizing the electrocatalytic activity of nanocomposites for r-MABs.

Conventional hydrogenation of lignin-derived compounds requires high H₂ pressures and temperatures, and yet, achieving the desired conversion and selectivity remains a challenge. Herein, a novel reaction system with a ruthenium catalyst and water as a solvent is developed for the selective hydrogenation of lignin-derived aromatics to corresponding ring-saturated products under ambient conditions (room temperature, and 1 bar H₂ pressure). Using a synergistic combination of catalytic experiments, advanced characterization techniques and quantum mechanical simulations, we elucidate that Ru catalyst switches its selectivity from deoxygenation in gas phase to ring hydrogenation in the condensed phase. Water partially dissociates and adsorbs on the catalyst surface as a combination of hydroxyl fragments, H atoms, and physisorbed molecules, and this is critical for Ru to flip its selectivity in the aqueous phase. Experimental results demonstrate a high conversion (>99 %) and >75 % selectivity towards the total hydrogenated products in the presence of water, corroborating the computational results in which kinetic free energy barriers for direct hydrogenation steps reduced to 70 kJ/mol and barrier for direct dehydroxylation increased from 63 kJ/mol to 202 kJ/mol in the case of phenol. Furthermore, H from dissociated water molecules is utilized in the hydrogenation and water also gets regenerated utilizing external hydrogen supply, thus acting as a shuttler for the external hydrogen.

The development of heterogeneous catalysts for converting abundant biomass feedstocks to higher value products is one of the most challenges these days. 2,5-dihydroxymethylfuran (DHMF) and 2,5-dihydroxymethyltetrahydrofuran (DHMTHF), synthesized from HMF hydrogenation, serve as crucial precursors in various applications. Non-noble metal catalysts are particularly attractive for this reaction, given their affordability and impressive catalytic efficiency. This work unveils the origin of the unique selectivity over Ni and Cu through mechanistic investigation using density functional theory (DFT), thermodynamic and kinetic analyses. The results emphasize that temperature and solvent play a crucial role in altering the energetic stabilities of intermediates, thereby influencing the energetic span (δG), turnover frequency (TOF), and selectivity of the reaction. The theoretical results align well with experimental observations. At 373.15 K, the highest TOF values over Ni and Cu are predicted in the HMF-to-DHMTHF path (1.79 × 10³h⁻¹) and the HMF-to-DHMF path (4.01 × 10⁵h⁻¹), respectively, in gas phase—under low dielectric constant ε condition. In contrast, the highest TOF value for Ni is observed in the HMF-to-DHMF path under implicit water condition (ε = 78.4) at 298.15 K. Competitive DHMF desorption and further hydrogenation influence the reaction’s selectivity. These insightful fundamental findings reveal key descriptors essential for designing new heterogeneous catalysts or enhancing existing ones, with the aim of potentially impacting biomass upgrading and other hydrogenation reactions.

The growing emphasis on decarbonization and the use of renewable energy has sparked considerable interest in ammonia (NH₃) synthesis under mild conditions, accompanied by the concurrent development of catalysts. Among these catalysts, BaO-promoted Ru has often been reported as a highly efficient catalyst for this reaction. Despite MgO being traditionally regarded as an optimal support for this catalytic system, its precise role has remained ambiguous. This study aims to elucidate the specific role of MgO as a support for Ru-BaO catalysts. Using pure MgO and MgO-Al₂O₃ mixed oxide (MgAlO_x) with different MgO contents (MgO wt% = 5, 30, and 70) as supports, catalysts impregnated with equal amounts of Ba and Ru were prepared and analyzed to explore their NH₃ synthesis activity and structural properties. Our observations reveal that while MgO does not directly promote Ru, it maintains robust basicity of BaO, enabling BaO to effectively function as an electronic promoter. In contrast, BaO supported on AlO_x domain shows suppressed basicity, resulting in inertness as a promoter. Consequently, the Ru-Ba/MgO catalyst forms highly active Ru-BaO-MgO interfacial sites, leading to significantly higher activity, lower activation energy, and a distinct reaction mechanism compared to Ru-Ba/MgAlO_x catalysts. This work sheds light on the importance of sequential interactions, i.e. support–promoter and promoter–active center interactions, in facilitating catalytic activity, thereby providing valuable insights essential for the design of advanced catalysts.

The selectivity and stability of catalysts for methanol synthesis from CO₂ still remain to be enhanced. In this work, we synthesized a series of Pd/ZrO₂ catalysts inversely loaded with various metal oxide promoters (ZnO, In₂O₃, and CeO₂), those would partially cover Pd metal surface and form some new metal-promoter interface, to explore the nature in the performance of CO₂ hydrogenation to methanol. The catalyst synthesized by this approach could limit the growth of Pd particles during the reduction and form new metal–metal oxide interfaces with different functions of CO₂ hydrogenation, improving the reaction performance of Pd-ZrO₂ catalysts. As a result, the ZnO-Pd/ZrO₂ catalyst exhibited the highest CO₂ conversion (12.0 %), methanol selectivity (95.6 %), and STY of methanol (472 g_MeOHkg_cat^-1h⁻¹), with excellent stability. The results of HRTEM, H₂-TPR, XPS, and XAFS showed that the ZnO-Pd/ZrO₂ catalyst had the typical Pd-ZnO interface with Pd²⁺ species after the H₂ reduction, which could enhance the adsorption and activation of CO₂. In addition, the in situ DRIFTS and NAP-XPS results implied that the Pd-ZnO interface significantly improved the formation of formate (HCOO*) and methoxy (H₃CO*) species, which were considered to be the key intermediates of methanol generation, and thus greatly enhanced the selectivity of methanol.

Regulating the selectivity of reaction pathways to desirable products via controlling adsorption/activation behaviors towards reactants is significant for the design of excellent catalysts for selective hydrogenation but remains challenging. Exemplified with dimethyl oxalate (DMO) hydrogenation, we herein propose an in situ exsolution strategy for constructing interfacial Ni⁰/Ni^δ+ sites by using pre-synthesized Ni phyllosilicate as the precursor to control the reaction pathways of selective hydrogenation. Structural characterizations, including in situ spectroscopic and isotopic studies, and theoretical calculations elucidate that the interfacial Ni⁰/Ni^δ+ sites can selectively activate monoester group of DMO via a tilted adsorption configuration and hence boost hydrogen dissociation. With such activation behaviors the reaction pathway is steered to methyl glycolate, other than the pathway to ethylene glycol on the reference active sites where both ester groups are activated and methyl formate is formed via breaking the C–C bond of DMO.