Heterogeneous Catalytic Materials Research Articles

A comparative study on the twinning boundaries of five-fold twinned copper and gold nanorods

Five-fold twinned copper and gold nanorods are important materials in heterogeneous catalysis. However, knowledges on the twinning boundary structures and their catalytic activities are quite limited. In this work, we conducted large-scale structure searching on the basis of forcefield potential and evolutionary algorithm, and precise quantum calculations on electronic structures and chemisorption energies using first-principles density functional theory. We determined the optimal twinning structures of the five-fold twinned copper and gold nanorods and analyzed their geometric differences via computing the standard deviation of metal bond lengths and the degrees of order. It was found that Au twinning boundary has a generally more regular structure but could involve noticeable point or line defects in some local areas, whereas Cu shows an incompact structure with fewer defects in the twinning region. Further by surface adsorption calculations using probe molecules of benzene and CO2, we show different degrees of chemisorption enhancement at various sites in or beside the twinning boundaries. Together with calculated charge transfer between adsorbates and metals or among different twinning regions, our results may provide some useful insights into the structural and chemisorption characteristics of twinned nanomaterials.

Editorial Special Issue “Heterogeneous Catalytic Materials: Synthesis, Characterization and Applications for Energetic Purposes”

Solid catalytic materials play a key role in the development of industrial chemistry, showing important advantages over liquid materials thanks to their easier separation from the reaction liquid medium, their reusability and stability, and their environmentally friendly character [...]

Nano High‐Entropy Materials: Synthesis Strategies and Catalytic Applications

The multicomponent combinations of metals in nanoscale high‐entropy materials (HEMs) have unique structure and physical and chemical properties, which provide them tailorable active sites and catalytic performance and attract intensive researches in recent years. Herein, an overview of the development of the synthesis strategies for various types of HEMs and their formation mechanisms is provided. These synthesis methods are compared, and their advantages and challenges are illustrated. The superior catalytic behavior of HEMs compared with their traditional analogue materials in heterogeneous catalysis are discussed and the underlying structure–activity correlation is revealed. The perspectives for future HEMs design are provided to achieve significant progress for catalytic applications.

Synthesis of stable and highly efficient Au@ZIF-8 for selective hydrogenation of nitrophenol

A series of nanoparticles (NPs) with different Au content was successfully encapsulated into metal organic framework ZIF-8 with highly porous structure through room-temperature crystallization. X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption and transmission electron microscopy were carried out to characterize the obtained Au@ZIF-8 heterogeneous catalytic material comprehensively. Au NPs were dispersed uniformly in the ZIF-8 and the Au NP diameter was 5–6 nm. The crystal structure of ZIF-8 was unchanged when compared with that before Au loading. It was found that the Au content plays an important role in the hydrogenation reaction. The obtained Au@ZIF-8 exhibited high hydrogenation activity to nitrophenol and excellent selectivity to aminophenol. The recyclability of the Au@ZIF-8 catalysts showed excellent catalytic performance and great stability in the recycling reaction.

Investigating the stability of graphitic carbon materials in electrocatalysis using electronic structure methods

As carbon materials are cheap and versatile, they are widely used materials for heterogeneous catalysis in general and for electrocatalysis in particular. However, they are prone to degradation, particularly under oxidative conditions. While electronic structure theory has been applied to study structure and thermodynamics in materials science, in many cases kinetic stability is the key feature which is associated with mechanisms and barriers. To compute these in aqueous medium and under electrode potential, we devise a DFT + implicit solvation scheme using a constant potential approach. Considering both pH and potential on a polycyclic aromatic hydrocarbon (PAH) model, we find a low energy pathway for graphitic carbon degradation. Depending on the pH and the potential, barrierless hydroxylation followed by deprotonation is observed at the PAH’s edges. At low pH and potential, the material is expected to remain pristine, at intermediate potential it exhibits few ketone and alcohol groups at its edges, and at high potential no barriers are found for hydroxylation processes, leading to CO2 formation and significant deformation of the material. We also observe smaller PAHs and nitrogen doped PAHs exhibit increased stability, which we attribute to their increased oxidation potentials.

Self‐Supported Electrocatalysts Derived from Nickel‐Cobalt Modified Polyaniline Polymer for H2‐Evolution and O2‐Evolution Reactions

AbstractThe water splitting aims to produce H2 for fuel cells and a number of industrial processes such as the ammonia synthesis and the metals refining. There is actually a major limitation about the development of cost‐effective and efficient electrocatalysts to lower the cell voltage that must be overcome to perform sequentially the overall reaction that is 2H2O →2H2+O2. In the present study, we combined Ni and Co as the promising alternative catalytic metals to Pt‐group metals as well as N and S as the doping elements to fabricate self‐supported electrocatalysts for hydrogen evolution (HER) and oxygen evolution (OER) in alkaline media. To these ends, the polymerization of the aniline into polyaniline (PANI) in the presence of Ni(II) and Co(II) followed by calcination in air resulted in the formation of heterogeneous catalytic materials self‐supported onto a matrix made of C, N, S, Ni and Co. Enhanced activity and durability were recorded for the hybrid and bimetallic PANI‐NiCo composite.

Controlling the Oxidation State of Pt Single Atoms for Maximizing Catalytic Activity.

Single-atom catalysts (SACs) have emerged as promising materials in heterogeneous catalysis. Previous studies reported controversial results about the relative level in activity for SACs and nanoparticles (NPs). These works have focused on the effect of metal atom arrangement, without considering the oxidation state of the SACs. Here, we immobilized Pt single atoms on defective ceria and controlled the oxidation state of Pt SACs, from highly oxidized (Pt0 : 16.6 at %) to highly metallic states (Pt0 : 83.8 at %). The Pt SACs with controlled oxidation states were then employed for oxidation of CO, CH4 , or NO, and their activities compared with those of Pt NPs. The highly oxidized Pt SACs presented poorer activities than Pt NPs, whereas metallic Pt SACs showed higher activities. The Pt SAC reduced at 300 °C showed the highest activity for all the oxidations. The Pt SACs with controlled oxidation states revealed a crucial missing link between activity and SACs.

Effects of transition metals on the evolution of polymer-derived SiOC ceramics

This study focuses on catalytic graphitization from different metals, iron (Fe), cobalt (Co), and nickel (Ni), for inducing carbon growth in silicon oxycarbides (SiOCs) during the pyrolysis. Fe, Co, and Ni-modified SiOCs were synthesized by pyrolysis to 900, 1100, and 1300 °C respectively in Ar. The transition metals induced the formation of the corresponding metal silicides, β-SiC, and graphitic carbon with the catalytic activity in the order of Fe > Co > Ni, in agreement with the activation energy calculation based on the carbon types and amounts. Lateral growth of turbostratic carbon followed a 2D grain growth process and its point-like defect density decreased based on the catalytic order of the transition metals, with SiOC/Fe having the lowest defect density. Quantitative analysis of the XPS results with Rietveld refinement illustrated that the phase separation of SiOC is more dominant than local carbothermal reduction between SiO2 and C in the SiOC/M (M = Ni, Co, or Fe) systems. Understanding the catalytic graphitization effect of Ni, Co, and Fe on polymer derived ceramics offers new strategies in increasing high-temperature phase amounts and thus creating novel materials for heterogeneous catalysis, magnetic, and other applications.

1D Co4S3 nanoneedle array with mesoporous carbon derived from double comb copolymer as an efficient solar conversion catalyst

This study investigates the use of a one-dimensional (1D) cobalt sulfide/mesoporous carbon heterogeneous electrocatalyst as counter electrode for high solar energy conversion efficiency in dye-sensitized solar cells (DSSCs). The 1D cobalt oxide (Co3O4) was in situ hydrothermally grown on the fluorine-doped tin oxide glass substrate, followed by sulfurization to form 1D cobalt sulfide (Co4S3) nanoneedle array. The Co4S3 is characterized by a high electrocatalytic activity for reducing/oxidizing the redox couple in the electrolyte. Additionally, the 1D structural feature of the Co4S3 allows fast electron transport through the oriented diffusion pathway. However, the Co4S3 still has relatively low chemical stability and poor electrical conductivity than conventional Pt catalyst. Herein, we incorporated the mesoporous carbon layer derived from the double comb copolymer, i.e., PVDC-g-POEM, which can act as a mesoporous structural template and sufficient carbon source. This strategy increased the electrocatalytic activity and chemical durability of the heterogeneous catalytic materials. The 1D Co4S3/mesoporous carbon heterogeneous catalyst exhibited excellent electrocatalytic activity for the reduction of triiodide, thereby outperforming the conventional Pt counter electrode. The catalytic properties were demonstrated by electrochemical analysis, i.e., cyclic voltammetry and electrochemical impedance spectroscopy. Results suggest that solid-state DSSCs (ssDSSCs) fabricated with the 1D Co4S3/mesoporous carbon counter electrode exhibited a higher solar energy conversion efficiency of 6.2% than the corresponding ssDSSC with conventional Pt (5.7%). The pure 1D Co4S3 or mesoporous carbon showed relatively lower performance than conventional Pt. Accordingly, the 1D Co4S3/mesoporous carbon synergetic approach represents a new strategy for enhancing the catalytic activity and chemical stability for highly efficient ssDSSCs.

Metal Organic Framework-Encapsulated Phosphotungstic Acid: An Effective Catalyst for Highly Efficient Acetalization of Vanillin Propylene Glycol

Metal organic frameworks (MOFs) have exhibited potential for application as heterogeneous catalytic materials because they consist of empty space, which can be used for encapsulation. Encapsulation of H3PW12O40 (HPW) in MOFs, such as the fabrication of MIL-101, by direct synthesis method or impregnation has drawn significant interest. However, few researches have used MOFs as catalysts for acetalization. This study evaluates the use of HPW encapsulated in MIL-101(Cr) to make it a catalyst in the acetalization of vanillin propylene glycol. Samples fabricated using various techniques (encapsulation and impregnation) were characterized by SEM, TEM, N2 adsorption–desorption, XRD, and FT-IR. The synthesis conditions of HPW@MIL-101 and their effects on vanillin conversion were examined. The reaction kinetics was also investigated under optimal conditions. Vanillin conversion showed that introducing HPW directly into MIL-101(Cr) during synthesis induced a 14% increase, compared with impregnation. The results indicated that HPW@MIL-101(Cr) is an effective method for vanillin propylene glycol acetal production and is reusable.

A Review on Bio-Based Catalysts (Immobilized Enzymes) Used for Biodiesel Production

The continuous increase of the world’s population results in an increased demand for energy drastically from the industrial and domestic sectors as well. Moreover, the current public awareness regarding issues such as pollution and overuse of petroleum fuel has resulted in the development of research approaches concerning alternative renewable energy sources. Amongst the various options for renewable energies used in transportation systems, biodiesel is considered the most suitable replacement for fossil-based diesel. In what concerns the industrial application for biodiesel production, homogeneous catalysts such as sodium hydroxide, potassium hydroxide, sulfuric acid, and hydrochloric acid are usually selected, but their removal after reaction could prove to be rather complex and sometimes polluting, resulting in increases on the production costs. Therefore, there is an open field for research on new catalysts regarding biodiesel production, which can comprise heterogeneous catalysts. Apart from that, there are other alternatives to these chemical catalysts. Enzymatic catalysts have also been used in biodiesel production by employing lipases as biocatalysts. For economic reasons, and reusability and recycling, the lipases urged to be immobilized on suitable supports, thus the concept of heterogeneous biocatalysis comes in existence. Just like other heterogeneous catalytic materials, this one also presents similar issues with inefficiency and mass-transfer limitations. A solution to overcome the said limitations can be to consider the use of nanostructures to support enzyme immobilization, thus obtaining new heterogeneous biocatalysts. This review mainly focuses on the application of enzymatic catalysts as well as nano(bio)catalysts in transesterification reaction and their multiple methods of synthesis.

Effect of Precious Metals on NO Reduction by CO in Oxidative Conditions

Carbon dioxide has become an environmental challenge, where the emissions have reached higher level than can be handled. In this regard, conversion of CO2 to value-added chemicals and thus recycling of CO2 appear a viable option. Prior to valorization, CO2 must be purified. Among several opportunities, oxyfuel combustion is a process in rapid development. However, the gases resulting from this process contain some traces of impurities that can hinder the recovery of CO2 such as NO and CO. This work has, therefore, focused on the study of the NO-CO reaction in an oxidizing medium, using heterogeneous catalytic materials based on various supported noble metals. These materials were extensively characterized by a variety of methods including Brunauer–Emmett–Teller (BET) surface area measurements, hydrogen chemisorption, transmission electron microscopy (TEM) and H2 temperature programmed reduction (H2-TPR). The results obtained show that the catalytic behavior of M/Al2O3 catalysts in CO oxidation and NO reduction with CO in oxidative conditions depends mainly on the nature of the metal. The best result for both reactions is obtained with Pt/Al2O3 catalyst. The Pt nanoparticles in their metallic form (Pt°) as evidenced by TPR could explain the activity.

Intermetallic compound PtMny-derived Pt−MnOx supported on mesoporous CeO2: Highly efficient catalysts for the combustion of toluene

Intermetallic compounds are a kind of important materials in heterogeneous catalysis. In this work, we first synthesized the PtMny intermetallic nanocrystals using the polyvinyl pyrrolidone-assisted ethylene glycol reduction method, and then loaded them on the surface of mesoporous CeO2 (meso-CeO2) derived from a KIT-6-templating route, generating the mPt−nMnOx/meso-CeO2 (m = 0−0.39 wt%, n = 0−1.21 wt%) catalysts after calcination at 500 °C in air. It is found that the as-obtained catalysts displayed an ordered mesoporous architecture with surface areas of 95−108 m2/g. The 0.37Pt−0.16MnOx/meso-CeO2 sample exhibited the best catalytic performance for toluene combustion (T50 % =162 °C and T90 % =171 °C at space velocity = 40,000 mL/(g h)). Kinetic analysis reveals that the apparent activation energy (57 kJ/mol) obtained over the best-performing 0.37Pt−0.16MnOx/meso-CeO2 sample was lower than those (63−75 kJ/mol) obtained over the other samples. Furthermore, the 0.37Pt−0.16MnOx/meso-CeO2 sample possessed good thermal stability and water-resistant performance. Benzyl alcohol, benzoic acid, and maleic anhydride were proven to be the main intermediates of toluene combustion, hence, toluene combustion might take place through a sequence of toluene → benzyl alcohol and benzoic acid → maleic anhydride → carbon dioxide and water, which might obey the Eley−Rideal reaction mechanism. It is concluded that loading of Pt and MnOx enhanced the adsorbed oxygen and Mn2+ species concentration and low-temperature reducibility, thus promoting toluene combustion over 0.37Pt−0.16MnOx/meso-CeO2.

Progress of Catalytic Valorization of Bio-Glycerol with Urea into Glycerol Carbonate as a Monomer for Polymeric Materials

Versatile polymers with highly adjustable characteristics and a broad range of applications are possibly developed owing to the contemporary industrial polymerization techniques. However, industrial production of large amounts of chemicals and polymers heavily depends on petroleum resources which are dwindling and unsustainable. Of particular interest is to utilize sustainable and green resources for the manufacture of polymeric materials. The efficient transformation of bio-glycerol to the relevant functional derivatives are being widely investigated owing to the increasing demand for enhancing the value of glycerol manufactured by biodiesel and oleochemical industries. With respect to glycerol-based polymer chemistry and technology, considering the economy and environmental benefits, using effective catalysts for the selective transformation of bio-glycerol and urea into glycerol carbonate (GC) as a polymer monomer is of great significance. In this review, recent studies on GC synthesis involving the catalysts such as zinc, magnesium, tungsten, ionic liquid-based catalysts, reaction conditions, and possible pathways are primarily described. Some critical issues and challenges with respect to the rational development of heterogeneous catalytic materials like well-balanced acid-base sites are also illustrated.

Pollutant degradation behaviors in a heterogeneous Fenton system through Fe/S-doped aerogel

To prepare a heterogeneous Fenton catalytic material with high pollutant degradation efficiency, Fe/alginate acid hydrogel was used as a template to obtain a Fe/S-doped aerogel (GFe2) and a Fe/O aerogel (GFe3). GFe2 and GFe3 exhibit different iron component crystal patterns; from our results, we deduced that S-doping improves the electron transportation in the Fenton reaction. GFe2 also exhibits a better spherical structure and a higher specific area than GFe3 due to the support of the FeS nanospheres. To further increase structural advantage, polyvinyl alcohol (PVA) was added to alginate hydrogel during in-situ pyrolysis, which further converts GFe2 into a more porous structure (PGFe). Experiments show that the organic removal efficiency of the samples are ordered as GFe3 < GFe2 < PGFe, which acts as additional evidence for the importance of S doping and the structural support that PVA offers which produces more active sites and faster electron transportation. PGFe shows a high reusability after 5 runs of repetitive use in tetracycline (TC) and perfluorooctanoic acid (PFOA) degradation. The removal rate of PFOA increased from 15.4% to 21.6% using PGFe; though not as significant as its effects on TC. The C7, C8, F23, and O24 atoms of PFOA are found easier to be attacked by hydroxyl radicals. Having used drinking and black odorous water to further evaluate the practical properties and industrial potentials of the aerogel, PGFe also shows a significant effect in degrading a variety of pollutants, both organic and heavy metal. This clearly demonstrates the promising potentials of Fe/S-doped carbon aerogel.

A Brief Summary of Research Progress on the Application of Rare Earth Materials in Heterogeneous Catalysis

A Brief Summary of Research Progress on the Application of Rare Earth Materials in Heterogeneous Catalysis

Study of the versatility of CuBTC@IL-derived materials for heterogeneous catalysis

The versatility of CuBTC (HKUST-1) MOF materials to be functionalized to improve their catalytic activity performance was evaluated. CuBTC@IL catalysts are selective for the cycloaddition of CO2 to epoxides, giving rise to value-added products.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites.

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

Dual-Ionically Bound Single-Site Rhodium on Porous Ionic Polymer Rivals Commercial Methanol Carbonylation Catalysts.

Novel porous polymers can serve as self-supporting solid carriers and provide abundant coordination or charged sites for single-site metals, and thus are emerging as advanced functional materials in heterogeneous catalysis for various transformations traditionally catalyzed by homogeneous systems. A brief overview of the development of this heterogenization given, including the recent advances regarding electrovalent bonds by employing charged supports represented by porous ionic polymers (PIPs), which is exemplified herein with a novel single-site Rh1 /PIP catalyst, featuring a new active site [Rh(CO)I3 ]2- dual-ionically bound onto a quaternary phosphonium cationic framework polymer, different from the single-ionically bound [Rh(CO)2 I2 ]- in previous studies. Such a unique metal configuration of Rh1 /PIP leads to excellent performance in vapor-phase methanol carbonylation, outperforming commercial homo- and heterogeneous catalysts.

Estimating vibrational and thermodynamic properties of adsorbates with uncertainty using data driven surrogates

AbstractIn this work, we propose a strategy to develop data driven local surrogate models of ab initio potential energy functions describing the interaction of adsorbates on heterogeneous catalytic materials. We show that these multivariable surrogate models, based on orthogonal polynomial expansion and trained on sampled ab‐initio energies/forces, can be used to compute harmonic vibrational frequencies and the entropy of adsorbates. Further, we show that the errors in our surrogate model can be estimated and propagated to calculate the uncertainty in the computed properties. We show proof‐of‐concept illustrations of our method to calculate the vibrational frequencies of ethene on 1D edges of molybdenum sulfide (MoS2), (b) 2D surfaces of Pt(111), and (c) 3D micropores of a HZSM‐5 zeolite; the entropy of ethane adsorbed on Pt(111); and the associated uncertainties in all the cases.