Heterogeneous Metal Catalysts Research Articles

Asymmetric Coupled Binuclear-Site Catalysts for Low-Temperature Selective Acetylene Semi-hydrogenation.

Heterogeneous metal catalysts with bifunctional active sites are widely used in chemical industries. Although their improvement process is typically based on trial-and-error, it is hindered by the lack of model catalysts. Herein, we report an effective vacancy-pair capturing strategy to fabricate 12 heterogeneous binuclear-site catalysts (HBSCs) comprising combinations of transition metals on titania. During the synthesis of these HBSCs, proton-passivation treatment and step-by-step electrostatic anchorage enabled the suppression of single-atom formation and the successive capture of two target metal cations on the titanium-oxygen vacancy-pair site. Additionally, during acetylene hydrogenation at 20 °C, the HBSCs (e.g., Pt1Pd1-TiO2) consistently generated more than two times the ethylene produced by their single-atom counterparts (e.g., Pd1-TiO2). Furthermore, the Pt1Pd1 binuclear sites in Pt1Pd1-TiO2 were demonstrated to catalyze C2H2 hydrogenation via a bifunctional active-site mechanism: initially C2H2 chemisorb on the Pt1 site, then H2 dissociates and migrates from Pd1 to Pt1, and finally hydrogenation occurs at the Pt1-Pd1 interface.

Controlled incorporation of Zn into nitrogen-doped porous carbon boosts the alcohol dehydrogenation to carboxylic acids

The dehydrogenation of primary alcohols to carboxylic acids is a crucial process in chemical industries such as fibers and plastics. Carboxylic acids, the resulting products, are not only important chemical raw materials but also fundamental pharmaceutical intermediates. Zn-based catalysts have gained attention as a promising option for this transformation owing to their economic cost and abundant reserves. However, stability issues, including structure collapse and morphological changes, have plagued the reported Zn-based catalysts during this transformation. In response to these challenges, this study focused on the design and development of Zn-based catalysts via controlled incorporation of Zn into nitrogen-doped porous carbon to modulate the numbers of defects and Lewis acid-base site pairs. Through extensive screening of various parameters, the best-performing catalyst, namely Zn@NC-800, exhibited high activity and remarkable stability, surpassing all the reported Zn-based catalysts. Moreover, this catalyst demonstrated great recyclability since it could maintain approximately 90 % yields after 9 cycles. Notably, the product formation rate of this catalyst could reach 3833 μmol·gcat.−1·h−1, exceeding that of most reported non-noble metal heterogeneous catalysts. Consequently, this study offers a promising approach for efficiently and stably catalyzing alcohol dehydrogenation reactions using non-noble metals.

Catalytic Applications in the Production of Hydrotreated Vegetable Oil (HVO) as a Renewable Fuel: A Review

The significance and challenges of hydrotreatment processes for vegetable oils have recently become apparent, encompassing various reactions like decarbonylation, decarboxylation, and hydrogenation. Heterogeneous noble or transition metal catalysts play a crucial role in these reactions, offering high selectivity in removing oxygen and yielding desired hydrocarbons. Notably, both sulphided and non-sulphided catalysts exhibit effectiveness, with the latter gaining attention due to health and toxicity concerns associated with sulphiding agents. Nickel-based catalysts, such as NiP and NiC, demonstrate specific properties and tendencies in deoxygenation reactions, while palladium supported on activated carbon catalysts shows superior activity in hydrodeoxygenation. Comparisons between the performances of different catalysts in various hydrotreatment processes underscore the need for tailored approaches. Transition metal phosphides (TMP) emerge as promising catalysts due to their cost-effectiveness and environmental friendliness. Ultimately, there is an ongoing pursuit of efficient catalysts and the importance of further advancements in catalysis for the future of vegetable oil hydrotreatment.

Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics into Six Products.

A full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2-supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, the application of oxygen-isolated characterization techniques proved indispensable in identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N-containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Towards the valorisation of glycerol by designing the surface chemistry of carbon xerogels by doping and oxygen functionalization

Research on innovative approaches to the valorisation of glycerol as a subproduct of biodiesel production has acquired an increasing demand in the development of a circular economy around energy generation, especially, in the line of improvement of the heterogeneous metallic catalysts used. In this regard, carbon xerogels have gained importance due to their stability and modifiability, while transition metals such as copper stand out as a cost-effective alternative, resulting in a technology where surface engineering plays a crucial role in achieving competitive catalytic activity. Building upon this, current research evaluates doped xerogels (Si, N, or GO) as supports of Cu and catalysts by themselves for glycerol oxidation. Benefits from the incorporation of oxygenated functional groups (OFG) were also evaluated. Results showed a consistently higher selectivity towards lactic acid (LA) across all catalysts and competitive catalytic conversion. In this performance, dopants played a crucial role in surface acid-base characteristics, while oxygenated functional groups (OFG) influenced copper adsorption, dispersion, and reducibility. Notably, the Cu/CXN-f catalyst demonstrated the highest LA yield by combining the effect of N as a doping species, with the presence of OFG and the formation of appropriated metallic Cu domains. This research underscores the potential of carbon xerogels in the tailored catalyst design, contributing to sustainable chemical production through their customizable textural and chemical properties.

Development Trends in Selective Hydrogenation Upgrading of 5-Hydroxymethylfurfural Catalyzed by Heterogeneous Metal Catalysts

Development Trends in Selective Hydrogenation Upgrading of 5-Hydroxymethylfurfural Catalyzed by Heterogeneous Metal Catalysts

Constructing Co@C nanoparticles with chainmail-structure for highly efficient hydroformylation of 1-hexene

Constructing highly active noble-metal-free heterogeneous catalysts is the crux for the hydroformylation of long-chain α-olefins. Herein, novel chainmail-structured cobalt oxide nanoparticles (CoO@C|SBA-15) are fabricated by the channel confinement strategy, which display excellent activity for the 1-hexene hydroformylation. Specifically, the obtained catalyst shows 100% 1-hexene conversion and 94% heptanal selectivity, as well as up to 2.0 linear to branch (l/b) ratio, outperforming most of heterogeneous noble metal catalysts. Remarkably, in-situ DRIFT spectra combined with density functional theory calculations disclosed the metallic Co derived from in-situ reconstruction of CoO is the key active site for 1-hexene hydroformylation. Specifically, the reconstructed Co site is responsible for the adsorption of 1-hexene, and the graphite carbon layer promotes the adsorption of H2 and CO by interacting with the reconstructed Co. Moreover, the graphite carbon layer provides a strong protective effect on the internal cobalt active sites and thus enhances the catalytic stability during the harsh condition. This work provides a new method for designing the low-cost heterogeneous catalyst and emphasizes the intrinsic active sites for 1-hexene hydroformylation reaction.

An efficient and stable LDH-derived Ni catalyst for highly selective hydrogenation of nitriles to primary amines

Transformation of nitriles into amines is highly desired, yet stable non-noble metal heterogeneous catalysts for efficiently selective production of primary amine are still lacking.Herein, for the first time we reported a Zr-doped yolk-shell structured Ni-based catalyst derived from layered double hydroxides (LDH) in the selective hydrogenation of nitriles to primary amines. The prepared catalyst exhibited higher primary amine yield (benzylamine yield >99.9 %) and significantly higher stability (>200 h) than highly efficient Ni catalysts that are reported previously in the selective hydrogenation of benzonitrile. Other nitriles are transformed into primary amines with good yields (90–100 %). The strong interaction between Ni0yolk and shell investsNiAl catalysts with robust stability. Importantly, Zr promotes the migration of Ni2+in the shell, resulting in appropriate acidity and better hydrogen activation capability, which drives the reaction aggressively to the BA formation pathway, and thussuccessfully enhances the yield of primary amine above 99.9 %.

Revealing the Role of Binary Distortion in PMS Activation over Spinel toward Efficient New Pollutants Removal

AbstractImproving peroxymonosulfate (PMS) activation efficiency to enhance simultaneous generation of radicals and non‐radicals is essential for removing new pollutants (NPs) in complex waters. However, achieving this with standard lattice‐structured heterogeneous catalysts remains challenging due to inefficient electron transfer. Here, CuCo2O4 properties are successfully tuned by controlling lattice distortion, enabling simultaneous PMS oxidation and reduction. Unlike the slow rate of electron transfer in heterogeneous metal catalysts with standard lattice structures, the highly active binary lattice distortion in CuCo2O4 alters the structure and electron distribution, exposes more Cu and Co sites, lowers the PMS adsorption barriers, and realizes the synergistic production of SO4•−/•OH), and 1O2. The k‐value for ciprofloxacin is as high as 17.83 min−1 M−1, 29.42 times higher than that with non‐binary lattice distortion. Additionally, the developed intermittent reactor consistently maintains a removal rate above 95% over five cycles in actual wastewater treatment scenarios. This work provides a new avenue for achieving the removal of new pollutants in complex water bodies.

Reactant-Induced Structural Evolution of Pt Catalysts Confined in Zeolite.

Reactant-induced structural evolutions of heterogeneous metal catalysts are frequently observed in numerous catalytic systems, which can be associated with the formation or deactivation of active sites. In this work, we will show the structural transformation of subnanometer Pt clusters in pure-silica MFI zeolite structure in the presence of CO, O2, and/or H2O and the catalytic consequences of the Pt-zeolite materials derived from various treatment conditions. By applying the appropriate pretreatment under a reactant atmosphere, we can precisely modulate the size distribution of Pt species spanning from single Pt atoms to small Pt nanoparticles (1-5 nm) in the zeolite matrix, resulting in the desirably active and stable Pt species for CO oxidation. We also show the incorporation of Fe into the zeolite framework greatly promotes the stability of Pt species against undesired sintering under harsh conditions (up to 650 °C in the presence of CO, O2, and moisture).

Scale-up of dehydrogenation reaction system via heterogeneous metal catalysts for the utilization of by-product glycerol from biodiesel production process

Due to the increased waste glycerol from biodiesel process, this study focuses on scale-up of a reaction system for glycerol dehydrogenation to lactic acid and its derivatives using the Pt/ZrO2 catalyst. A concentration–time profile was obtained, based on which reaction mechanism and a reaction rate model were determined. The Langmuir–Hinshelwood model was used to develop the reaction rate model, which accurately predicted conversion of glycerol and yield of lactate, within a 5% error bounds. Based on these predictions, the volume of a continuous stirred-tank reactor (CSTR) was successfully estimated under the same reaction conditions. The calculated volume was approximately 60% of the batch volume indicating that reactor can become significantly more compact if the continuous reactor type could be used. Additionally, a pilot-scale CSTR volume was calculated by reflecting the adjusted reaction rate parameters, which were estimated from the experimental study of the pelletized catalyst. Furthermore, a reaction system with three CSTRs in series could reduce the total reactor volume by 65% than that obtained using a single CSTR. The results could be used as basic data for the scale-up of the continuous reaction system, where glycerol dehydrogenation takes place over the Pt/ZrO2 catalyst.

Green Catalysts for Sustainable Biodiesel Production from Waste Cooking Oil

Biodiesel manufacturing from waste cooking oil has emerged as a potential alternative in the search of sustainable energy. This process helps mitigate environmental pollution and reduces reliance on fossil fuels. This research examines the catalytic efficiency of environmentally friendly catalysts in this process, with a specific emphasis on catalysts based on enzymes. It assesses their effectiveness in terms of the production of biodiesel, the rate of the chemical reactions, cost efficiency, and their influence on the environment. Experimental evidence demonstrates that enzyme-based catalysts have enhanced catalytic activity, leading to an average biodiesel production of 90%, outperforming traditional catalysts such as solid acids, bases, and heterogeneous metal catalysts. Moreover, enzyme catalysts exhibit enhanced reaction rates due to their unique enzymatic activity and gentle reaction conditions. The cost study shows that the manufacturing costs for enzyme catalysts are competitive, with an average total cost of $800, which is equivalent to traditional catalysts. Environmental impact evaluation emphasizes the sustainability of enzyme catalysts by demonstrating their lower energy consumption, waste production, and greenhouse gas emissions compared to traditional alternatives. The results highlight the capacity of green catalysts, namely enzyme-based catalysts, to enhance sustainable biodiesel production methods, hence promoting a more eco-friendly and robust energy framework.

α-Alkylation of ketones with primary alcohols by an active non-noble metal Cu/CuOx catalyst.

Development of convenient and effective heterogeneous non-noble metal catalysts for α-alkylation of ketones with alcohols is challenging in heterogeneous catalysis. Here, we report active non-noble metal Cu/CuOx catalysts for the construction of C-C bonds by the α-alkylation of ketones with alcohols through the borrowing hydrogen methodology. The optimal Cu/CuOx-250 catalyst exhibits good catalytic performance in the reactions to give the corresponding products in 50-96% yields. The Cu/CuOx catalysts are characterized by different analysis techniques such as XRD, TEM, XPS, H2-TPR, BET, and ICP. Moreover, the catalyst can be reused at least for five successive cycles without significant loss of activity. The present study provides meaningful insights into the development of non-noble metal heterogeneous catalysts for α-alkylation of ketones with alcohols.

Recent advances and perspective on transition metal heterogeneous catalysts for efficient electrochemical water splitting

AbstractThe development of advanced technology for producing high‐purity and low‐cost hydrogen is crucial for the upcoming hydrogen economy. One of the most promising technologies to achieve carbon peak and carbon neutrality is hydrogen production through water electrolysis coupled with renewable energy. However, the efficiency of water electrolysis is limited by the catalyst material employed, thereby the pursuit of highly efficient catalysts is of paramount scientific significance. In this review, we focus on the synthesis of electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) through various strategies such as hydrogen spillover, heterostructure construction, element doping, monatomic construction, LDH structure modification, high entropy alloy, and other approaches. The article also provides a comprehensive overview of the challenges encountered in enhancing the activity, stability, and durability of transition metal heterogeneous catalysts for both HER and OER. Moreover, the mechanisms of HER and OER are illustrated. The electrocatalysts prepared by these strategies have exhibited promising results in terms of water splitting performance. However, there are still unresolved issues that need to be addressed, such as improving long‐term stability and reducing overall cost. Future prospects include exploring new materials and optimizing the preparation methods to further enhance the electrocatalytic activity.

Recent Advances in the Reverse Water-Gas Conversion Reaction.

The increase in carbon dioxide emissions has significantly impacted human society and the global environment. As carbon dioxide is the most abundant and cheap C1 resource, the conversion and utilization of carbon dioxide have received extensive attention from researchers. Among the many carbon dioxide conversion and utilization methods, the reverse water-gas conversion (RWGS) reaction is considered one of the most effective. This review discusses the research progress made in RWGS with various heterogeneous metal catalyst types, covering topics such as catalyst performance, thermodynamic analysis, kinetics and reaction mechanisms, and catalyst design and preparation, and suggests future research on RWGS heterogeneous catalysts.

Fluorescent Noncovalent Organic Framework for Supporting Gold Nanoparticles as Heterogeneous Catalyst with Merits of Easy Detection and Recycle.

A porous noncovalent organic framework with AIE effect is designed and synthesized as the support for gold nanoparticles (AuNPs). The framework is fabricated through the electrostatic complexation between carboxymethyl cellulose and tetraphenylethene-containing ammonium surfactant, which can complex AuNPs via the noncovalent interactions to offer a heterogeneous catalyst. Compared to the covalent modification on cellulose, this noncovalent framework gains superiorities in the catalyst synthesis and the size control of AuNPs. The AIE property and water-insolubility allow such heterogeneous catalysts to be easily detected, separated, and recycled, opening a new pathway for the reduction of nitrobenzene compounds and some dye compounds in aqueous conditions, which present the features of green chemistry. The use of cellulose for developing new heterogeneous metal catalysts, especially in a noncovalent way, would promote the value-added utilization of cellulose. This work provides a design strategy for gaining heterogeneous metal catalysts by taking advantage of natural bioresources.

Atomically‐Dispersed Metal Heterocatalysts: A Practical Step Toward Sustainability

AbstractAtomically‐dispersed heterogeneous metal catalysts can be considered as an “upgraded” version of classical solid metal catalysts. Unlike traditional heterogeneous metallic catalysts that contain nanoparticles or bulk micro‐sized transition metal species, the active sites of these novel types of catalysts are atomically distributed on the support's surface. This provides several advantages compared to classical catalysts such as higher activity and need for just very small amounts of metal precursors for the catalyst preparation. The latter issue is a key point in green chemical processes and of importance to achieve low‐cost pathways for industrial‐scale synthesis. The atomically dispersed metal sites permit a maximum of metal dispersion and additionally allow to achieve more reproducible heterogeneous catalysts. This review summarizes an overview on breakthrough findings in synthesis, applications and characterization techniques developed in the area of single‐atom, dual‐atom, single‐atom‐layer, single‐site as well as single‐atom nanozyme/enzyme catalysis. The characteristics and properties of each system provide an appropriate understanding for designing a nanomaterial that is optimized for a specific requirement.

The Acquisition of Primary Amines from Alcohols through Reductive Amination over Heterogeneous Catalysts

The synthesis of primary amines via the reductive amination of alcohols involves a hydrogen-borrowing or hydrogen-transfer mechanism, which consists of three main steps: alcohol hydroxyl dehydrogenation, carbonyl imidization, and imine hydrogenation. Heterogeneous catalysts are widely used for this reaction because of their high performance and amenability to separation and reuse. However, the efficiency of reductive amination is limited by the dehydrogenation step, which is severely affected by the competitive adsorption of NH3. We hope to improve the efficiency of reductive amination by increasing dehydrogenation efficiency. Therefore, in this overview, we introduce the research progress of alcohol reductive amination reaction catalyzed by heterogeneous metal catalysts, focusing on methods of enhancing dehydrogenation efficiency by screening the metal component and the acidity/alkalinity of the support. Finally, we propose some new strategies for the preparation of catalysts from the perspective of overcoming the competitive adsorption of NH3 and speculate on the design and synthesis of novel catalysts with high performance in the future.

Advances in Selective Hydrogenation of 5-Hydroxymethylfurfural over Heterogeneous Metal Catalysts

Biomass is an excellent renewable organic energy in nature. 5-hydroxymethylfurfural (HMF) is a significant platform chemical derived from biomass. It can be obtained from biomass and has the potential to produce high value-added derivatives. For the past few years, the chemocatalysis pathway has been extensively studied and is the main pathway of HMF transformation. In this paper, the influence factors and reaction mechanisms of different catalyst types on HMF hydrogenation processes were discussed. The latest progress on the efficient catalytic system using hydrogen, alcohol and other hydrogen sources to catalyze HMF was introduced. Future research prospects of catalytic hydrogenation of HMF were also prospected.

Pd@MgAl LDH/2-ThCA: A sustainable, active and recyclable nanocatalyst system for the rapid and efficient catalytic reduction of organic pollutants

Catalytic reduction of toxic pollutants such as nitroaromatics and organic dyes found in water/wastewater by heterogeneous nano-structured metallic catalysts is a promising method for wastewater treatment. The need for effective and reusable catalyst systems is recently increasing due to the soaring water pollution. For this purpose, in this study, a newly Pd@MgAl LDH/2-ThCA catalyst system was successfully developed by depositing palladium nanoparticles onto a modified MgAl LDH support, characterized and then used to eliminate these contaminants in the presence of NaBH4. Catalytic applications indicated that Pd@MgAl LDH/2-ThCA catalyst efficiently reduced 2-nitroaniline (2-NA), 4-nitrophenole (4-NP), 4-nitroaniline (4-NA), and 4-nitro-o-phenylenediamine (4-NPDA) with rate constants of 0.011 s−1, 0.0075 s−1, 0.017 s−1, and 0.02 s−1, respectively. Additionally, Pd@MgAl LDH/2-ThCA successfully degraded methyl orange (MO) and rhodamine B (RhB) with rate constants of 0.019 s−1 and 0.015 s−1, respectively. Furthermore, it was found that methylene blue (MB) was immediately degraded by Pd@MgAl LDH/2-ThCA. Reusability tests revealed that Pd@MgAl LDH/2-ThCA maintained its activity/stability after the 5 successive cycles, verifying its practical application potential. This paper reveals that Pd@MgAl LDH/2-ThCA is an effective, sustainable, and alternative catalyst system for the treatment of toxic environmental pollutants.