Heterogeneous Catalytic Reactions Research Articles

Rapid removal of methylene blue by a heterogeneous photo-Fenton process using economical and simple-synthesized magnetite–zeolite composite

A hetero-Fenton zeolite-supported Fe3O4 catalyst was synthesized using a simple impregnation–precipitation method. The structure, morphology, and components of the catalyst were characterized using various analytical methods (XRD, SEM, and ICP-MS). Subsequently, the catalyst was used to degrade the azo dye methylene blue (MB), via a heterogeneous photo-Fenton process under UV irradiation in an aqueous solution. This study investigated the influence of different parameters on MB decolorization efficiency, such as the initial concentration of hydrogen peroxide, amount of catalyst, initial dye concentration, and reusability of the catalyst. The removal efficiency was nearly 100% within only 5 min with an initial concentration of methylene blue of 50 mg L−1 under the following experimental conditions: a pH solution of 3, a catalyst of 0.6 g L−1, an H2O2 concentration of 66 mg L−1, and a UV lamp power of 6 W. Moreover, the Fe3O4/zeolite A catalyst (Fe/ZA) showed good stability in the photo-Fenton degradation of methylene blue after four consecutive cycles, implying that the Fe/ZA catalyst could be a potential wastewater treatment option. Furthermore, the findings of the reaction kinetics study demonstrate that the kinetics of the dye removal reaction can be fitted using the Langmuir–Hinshelwood model for heterogeneous catalytic reactions.

Recent Progress of Single‐Atom Alloys in Heterogeneous Catalytic Reactions

AbstractIn decades, heterogeneous catalysis has played a more significant role in social progress. However, the exorbitant price and low reserves vastly limit the application of noble metal catalysts, which are extensively used in heterogeneous catalysis. The single‐atom‐alloy catalysts (SAAs) have been regarded as a crucial way to improve the dispersion ratio of noble metal while maintaining great heterogeneous catalytic performance by dispersing noble metal single atoms on the surface of another metal. Besides the benefit from the metal bonds between noble metals and support metals, SAAs is also a unique method to construct metallic metal single atoms and obtain its characteristic catalytic performance, which is not possessed by other single atoms catalysts with positive electricity metal atoms. Most recently, SAAs have been demonstrated to catalyze a lot of significant heterogeneous reactions. This review will introduce the synthesis methods of SAAs and then summarize their applications in heterogeneous catalysis.

Hydrogen for CO2 processing in heterogeneous catalytic reactions

Efficient catalytic technologies for converting CO2 with hydrogen into value-added chemicals and fuels can help to solve the environmental problems related with large CO2 emissions. Among of the most interesting products that can be synthesized from CO2 are synthetic natural gas, methanol and DME, methane and higher hydrocarbons, higher alcohols. In this mini review, we highlight the recent advances in the development of heterogeneous catalysts and processes for of CO2 hydrogenation to these products. Recent research to develop highly active and selective catalysts based on controlled synthesis – active phases, promoters, supports, thermodynamics, are presented.

ABOUT THE POSSIBILITY OF USING THERMOCHEMICAL GAS ANALYZERS IN A MULTICOMPONENT MIXTURE

Kinetic parameters finding’s method of heterogeneous catalytic oxidation reactions of combustible gas’s small impurities in air on a thin platinum wire was described. It consists in obtaining from the wire’s current-voltage characteristic the dependence of the critical current values on its mass fraction in air. They corresponding to the catalytic ignition and extintion of the gas impurity. A method of determining the content of two combustible gases in the air, what based on processing the platinum wire’s current-voltage characteristic, was proposed. Depending on the level of the total gases concentration in the air, the determining experimental characteristics are not only the wire (catalyst) overheating relative to the inert wire under the conditions of catalytic ignition, but also the wire overheating during catalytic extinguishing or under conditions of self-sustaining catalytic combustion (without electric current heating).

Heterogeneous catalytic reaction of NO2 to HONO on hematite

The heterogenous catalytic reactions of NO2 on mineral dusts represent one of the important sources of HONO that promote the formation of O3 and other air pollutants, but the mechanism is poorly understood. First principles calculations, including a Hubbard-like +U correction and a dispersion correction, were employed to investigate the heterogeneous interaction of NO2 on the hematite (0001) surface. The competitive adsorption between the most common gas molecules in polluted air (NO2, CO, SO2, O3, H2O, O2, and N2) were also investigated. Under dry conditions, the (NO3δ−)(NOδ+) intermediate species can transform into surface NO3 and gaseous NO. Under wet conditions, the simulations predicted the production of HONO and HNO3 through the hydrolysis of NO2 via (NO3δ−)(NOδ+). Adsorption energies show that the surface Fe site provides strong interactions. Charge transfer occurs from the Fe atom to the adsorbate molecules. This study may facilitate the understanding of the transformations of the atmospheric gas pollutants on naturally occurring mineral dust aerosols. The heterogenous reaction may impact on global atmospheric chemistry.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnOx), an adsorption-enhanced catalyst (MnOx-PP) was constructed for catalytic organic dyes oxidative-degradation. MnOx-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnOx-PP obtains lower ionization potential and O2 adsorption energy to promote the continuous generation of active substance (O2*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts.

Characterizing the Water-Forming Reaction on Graphite- and Ceria-Supported Palladium Nanoparticles and Nanoislands by the Work Function

The water-forming reaction (WFR) between oxygen and hydrogen on metal surfaces is an important reaction in heterogeneous catalysis. Related research mostly focused on crystalline metal surfaces and thick films; however, supported nanoparticles (NP) have been rarely considered as well as a possible influence of the support on the NP catalytic activity. Here, we report on the WFR on graphite-supported palladium NPs and nanoislands (NI), which are characterized at room temperature and under ultrahigh vacuum conditions (UHV) by scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), Kelvin probe force microscopy (KPFM), and X-ray photoemission spectroscopy (XPS). We show that during the first cycles of sequential O2 and H2 pulses, atomic H reacts off preadsorbed atomic O, which can be followed by KPFM via monitoring the change in work function (WF) at the NPs and NIs. However, after a few WFR cycles, the WF changes get smaller and the mean WF of the Pd increases due to an irreversible deactivation of the catalyst: a filament structure is formed on the facets by O and C, which the latter probably gets released from the graphite during the WFR. In strong contrast to the Pd/graphite catalyst, the WFR can be followed without any changes during an unlimited number of cycles on a carbon-free Pd/cerium oxide/Cu(111) catalyst, which clearly shows that the support plays a role in the WFR on nanometer-sized Pd catalysts.

Insights into the mechanism of persulfate activation with carbonated waste metal adsorbed resin for the degradation of 2,4-dichlorophenol

Superabsorbent resin (SAR) saturated with heavy metals poses a threat to surrounding ecosystem. To promote the reutilization of waste, resins adsorbed by Fe2+ and Cu2+ were carbonized and used as catalysts (Fe@C/Cu@C) to activate persulfate (PS) for 2,4-dichlorophenol (2,4-DCP) degradation. The heterogeneous catalytic reaction was mainly responsible for 2,4-DCP removal. The synergistic effect of Fe@C and Cu@C was propitious to 2,4-DCP degradation. Fe@C/Cu@C with a ratio of 2:1 showed the highest performance of 2,4-DCP removal. 40 mg/L 2,4-DCP was completely removed within 90 min under reaction conditions of 5 mM PS, pH = 7.0 and T = 25 °C. The cooperation of Fe@C and Cu@C facilitated the redox cycling of Fe and Cu species to supply accessible PS activation sites, enhancing ROS generation for 2,4-DCP degradation. Carbon skeleton enhanced 2,4-DCP removal via radical/nonradical oxidation pathways and via its adsorption to 2,4-DCP. SO4˙ˉ, HO˙ and O2•− were the dominate radical species involved in 2,4-DCP destruction. Meanwhile, the possible pathways of 2,4-DCP degradation were proposed based on GC-MS. Finally, recycling tests proved catalysts exhibited recyclable stability. Aiming to resource utilization, Fe@C/Cu@C with satisfactory catalysis and stability, is promising catalyst for contaminated water treatment.

Photocatalytic CO2 capture on plasmonic copper nanoparticles in a biofluidic channel

A CO2 capture and photocatalytic conversion system was designed to investigate heterogeneous catalytic reactions in a biofluidic channel. The photo-reacted species produced in a microalgae fluid sample were analyzed using in situ Raman scattering and gas chromatography with mass spectroscopy (GC–MS). Nanopore copper (II) sulfide–hollow nanospheres (CuS–HNS) and copper nanocubes (CuNCs) were exposed under the visible laser irradiation during photoreduction process under hydrated conditions. Several products of C1–C4 species from CO2 were identified during photocatalytic reaction depending on the surface reaction conditions. Spectral features and time-dependent Raman spectral behaviors were different from CuS–HNS and CuNCs. Representative species of methanol (C1) and acetone (C3) during CO2 reduction reaction were examined at 633 nm. Adsorption of CO2 onto Cu surface was studied to interpret the photocatalytic reactions using the density functional theory (DFT) calculations. Based on different spectral changes of Raman spectra onto CuS–HNS and CuNCs surfaces in a biofluidic mixture of Spirulina maxima solutions, microalgae appeared to have the potential to play significant roles in carbon capture.

Dual-atom Co-Fe catalysts for oxygen reduction reaction

Controlled synthesis of dual-atom catalysts (DACs) for heterogeneous catalytic reactions is vital but still demanding. Herein, we construct a novel dual-atom catalyst containing FeN3-CoN3 sites on N-doped graphene nanosheets (CoFe-NG), which exhibits remarkable catalytic performance with a half-wave potential of 0.952 V for oxygen reduction reaction (ORR) and shows higher endurance to methanol/carbon monoxide poisoning and better durability than commercial Pt/C. The assembled Zn-air battery with CoFe-NG as the air electrode delivers a peak power density of 230 mW cm–2 and exhibits negligible change in output voltage at 5 mA cm–2 for 250 h. Theoretical calculations reveal that FeN3-CoN3 sites on N-doped graphene exhibit lower ORR barrier than FeN4 and CoN4 sites, and the rate-limiting step on the former is the transformation of *OH intermediate to H2O, different from the transformation of *O to *OH on the FeN4 site and the transformation of O2 to *OOH on the CoN4 site.

Operando magnetic resonance imaging of product distributions within the pores of catalyst pellets during Fischer–Tropsch synthesis

The optimization of a heterogeneous catalytic process requires characterization of the catalyst at industrially relevant conditions and length scales. Here we use magnetic resonance imaging to gain insight into the Fischer–Tropsch synthesis occurring in a pilot-scale fixed-bed reactor operating at 220 °C and 37 bar, for three H2/CO feed ratios. The molecular diffusion and carbon number of the hydrocarbon products are spatially resolved within both the reactor and individual 1 wt% Ru/TiO2 catalyst pellets. These data highlight the importance of mass transfer, in addition to the nanoscale catalyst activity, on catalyst performance. In particular, a start-up time of up to three weeks is required for the steady state to be achieved in the catalyst pores. Further, the average carbon number present in the pores can be as much as double that in the product wax. The operando characterization of water and oxygenates present in the pores is also achieved. The presence of a water-rich liquid at the pore surface is confirmed. The practical optimizations of heterogeneous catalytic processes and reactor engineering are intertwined, but often what occurs inside the reactor remains elusive. Now, the molecular diffusion and carbon number of hydrocarbon products during Fischer–Tropsch synthesis on a Ru/TiO2 catalyst are spatially resolved via magnetic resonance imaging in a pilot-scale fixed-bed reactor.

Numerical simulation of a heterogeneous catalytic batch reactor to produce biodiesel from vegetable oil

Numerical simulation of a heterogeneous catalytic batch reactor to produce biodiesel from vegetable oil

Rate Equations of Structure-Sensitive Catalytic Reactions with Arbitrary Kinetics

A general mathematical framework for the quantitative description of the cluster size dependence in heterogeneous catalytic reactions has been developed based on an analysis of the Gibbs energy of elementary reactions. The methodology was illustrated for a generic linear sequence of elementary reactions with three steps, a multi-step mechanism of ethanol oxidation comprising linear, nonlinear and quasi-equilibria steps and a network of parallel reactions in transformations of furfural.

Performance of Cu/ZnO Nanosheets on Electrospun Al2O3 Nanofibers in CO2 Catalytic Hydrogenation to Methanol and Dimethyl Ether

The synthesis of methanol and dimethyl ether (DME) from carbon dioxide (CO2) and green hydrogen (H2) offers a sustainable pathway to convert CO2 emissions into value-added products. This heterogeneous catalytic reaction often uses copper (Cu) catalysts due to their low cost compared with their noble metal analogs. Nevertheless, improving the activity and selectivity of these Cu catalysts for these products is highly desirable. In the present study, a new architecture of Cu- and Cu/Zn-based catalysts supported on electrospun alumina nanofibers were synthesized. The catalysts were tested under various reaction conditions using high-throughput equipment to highlight the role of the hierarchical fibrous structure on the reaction activity and selectivity. The Cu or Cu/ZnO formed a unique structure of nanosheets, covering the alumina fiber surface. This exceptional morphology provides a large surface area, up to ~300 m2/g, accessible for reaction. Maximal production of methanol (~1106 gmethanolKgCu-1∙h-1) and DME (760 gDMEKgCu-1∙h-1) were obtained for catalysts containing 7% wt. Cu/Zn with a weight ratio of 2.3 Zn to Cu (at 300 °C, 50 bar). The promising results in CO2 hydrogenation to methanol and DME obtained here point out the significant advantage of nanofiber-based catalysts in heterogeneous catalysis.

Application of Heterogeneous Catalytic Ozonation in Wastewater Treatment: An Overview

Catalytic ozonation is a non-selective mineralization technology of organic matter in water by using active free radicals generated by ozone degradation. Catalytic ozonation technology can be divided into homogeneous catalytic reactions using metal ions as catalysts and heterogeneous catalytic reactions using solid catalysts. Homogeneous catalytic ozonation technology has many problems, such as low mineralization rate, secondary pollution caused by the introduction of metal ions and low utilization efficiency of oxidants, which limit its practical application. Compared with homogeneous catalytic ozonation technology, heterogeneous catalytic ozonation technology has the advantages of easy recovery, lower cost of water treatment, higher activity and improved mineralization rate of organic matter. This overview classifies and describes catalysts for heterogeneous catalytic ozonation technology, including the different types of metal oxides, metal-free catalysts, and substrates used to immobilize catalysts. In addition, the heterogeneous catalytic ozonation process involved in the multiphase complex reaction process is discussed. The effects of different parameters on the performance of heterogeneous catalytic ozonation are also discussed.

Catalytic Distillation of Atmospheric Residue of Petroleum over HY-MCM-41 Micro-Mesoporous Materials

Catalytic distillation is a technology that combines a heterogeneous catalytic reaction and the separation of reactants and products via distillation in a single reactor/distillation system. This process combines catalysis, kinetics, and mass transfer to obtain more selective products. The heterogeneous catalyst provides the sites for catalytic reactions and the porous surface for liquid/vapor separation. The advantages of catalytic distillation are energy savings, low waste streams, catalyst longevity, higher conversion, and product selectivity; these properties are interesting for petrochemical and petroleum industries. For this study, 100 mL of atmospheric residue of petroleum (ATR) was distilled in the presence of 1.0 g of a micro/mesoporous catalyst composed of a HY-MCM-41, and the reactor used was an OptiDist automatic distillation device, operating according to ASTM D-86 methodology. The products were collected and analyzed by gas chromatography. The samples of ATR, HY/ATR, and HY-MCM-41/ATR were analyzed by thermogravimetry (TG) to determine the activation energies (Ea) relative to the thermal decomposition of the process, using the Ozawa–Flynn–Wall (OFW) kinetic model. The obtained results show a potential catalytic distillation system for use in the reaction of heavy petroleum fractions and product separation from the HY/MCM-41 micro/mesoporous catalyst. The TG data revealed two mass loss events for ATR in the ranges of 100–390 and 390–590 °C, corresponding to volatilization and thermal cracking, respectively. The Ea determined for the thermal degradation of the ATR without a catalyst was in the range of 83–194 kJ/mol, whereas in the presence of the HY-MCM-41 catalyst, it decreased to 61–105 kJ/mol, evidencing the catalytic effect of the micro-mesoporous material. The chromatography analysis allowed for the identification of gasoline and a major production of diesel and gasoil when the HY-MCM-41 mixture was used as the catalyst, evidencing the synergism of the combined effect of the acid sites, the crystalline phase, and the microporosity of the HY zeolite with the accessibility of the hexagonal mesoporous structure of the MCM-41 material.

In situ diffraction monitoring of nanocrystals structure evolving during catalytic reaction at their surface

With decreasing size of crystals the number of their surface atoms becomes comparable to the number of bulk atoms and their powder diffraction pattern becomes sensitive to a changing surface structure. On the example of nanocrystalline gold supported on also nanocrystalline {text{CeO}}_2 we show evolution of (a) the background pattern due to chemisorption phenomena, (b) peak positions due to adsorption on nonstoichiometric {text{CeO}}_{2-x} particles, (c) Au peaks intensity. The results of the measurements, complemented with mass spectrometry gas analysis, point to (1) a multiply twinned structure of gold, (2) high mobility of Au atoms enabling transport phenomena of Au atoms to the surface of ceria while varying the amount of Au in the crystalline form, and (3) reversible {text{CeO}}_2 peaks position shifts on exposure to He–X–He where X is O2, H2, CO or CO oxidation reaction mixture, suggesting solely internal alternations of the {text{CeO}}_2 crystal structure. We found no evidence of ceria lattice oxygen being consumed/supplied at any stage of the process. The work shows possibility of structurally interpreting different contributions to the multi-phase powder diffraction pattern during a complex physico-chemical process, including effects of physi-, chemisorption and surface evolution. It shows a way to structurally interpret heterogeneous catalytic reactions even if no bulk phase transition is involved.

KIT-5 Structural and Textural Changes in Response to Different Methods of Functionalization with Sulfonic Groups.

In this project, KIT-5 materials were effectively functionalized with sulfonic groups introduced by grafting or the co-condensation method and tested as heterogeneous solid acid catalyst. A co-condensation procedure leading to the stable, -SO3H functionalized KIT-5 materials was successfully established. Moreover, the influence of both synthesis methods on the structural and textural parameters, as well as surface chemistry, morphology, and catalytic activity of -SO3H/KIT-5 materials was thoroughly investigated. The syntheses with 3-mepkaptopropyltrimethoxysilane (MPTMS) acting as a modifying agent resulted in samples in which functional groups were introduced into the structure and/or onto the mesoporous silica surface. The oxidation stage of -SH to -SO3H groups was carried out under mild conditions, using a "green" oxidant (H2O2). The application of different functionalization techniques and the introduction of different amounts of modifying agent allowed for an evaluation of the influence of these parameters on the ordering of the mesoporous structure of KIT-5 materials. The applied methods of assessment of the physicochemical parameters (XRD, low-temperature N2 sorption, TEM) showed that, especially when the co-condensation method was applied, as the number of functional groups increased, the ordering of structure characteristic of KIT-5 decreased. On the other hand, the samples modified by grafting had a stable structure, regardless of the amount of introduced MPTMS. Test reactions carried out on the basis of Friedel-Crafts alkylation process showed that the synthesized materials can be considered promising acid catalysts in heterogeneous catalysis reactions.

Oxygen vacancy-engineered titanium-based perovskite for boosting H2O activation and lower-temperature hydrolysis of organic sulfur

Modulation of water activation is crucial to water-involved chemical reactions in heterogeneous catalysis. Organic sulfur (COS and CS2) hydrolysis is such a typical reaction involving water (H2O) molecule as a reactant. However, limited by the strong O-H bond in H2O, satisfactory CS2 hydrolysis performance is attained at high temperature above 310°C, which is at the sacrifice of the Claus conversion, strongly hindering sulfur recovery efficiency improvement and pollution emissions control of the Claus process. Herein, we report a facile oxygen vacancy (VO) engineering on titanium-based perovskite to motivate H2O activation for enhanced COS and CS2 hydrolysis at lower temperature. Increased amount of VO contributed to improved degree of H2O dissociation to generate more active -OH, due to lower energy barrier for H2O dissociation over surface rich in VO, particularly VO clusters. Besides, low-coordinated Ti ions adjacent to VO were active sites for H2O activation. Consequently, complete conversion of COS and CS2 was achieved over SrTiO3 after H2 reduction treatment at 225°C, a favorable temperature for the Claus conversion, at which both satisfying COS and CS2 hydrolysis performance and improved sulfur recovery efficiency can be obtained simultaneously. Additionally, the origin of enhanced hydrolysis activity from boosted H2O activation by VO was revealed via in-depth mechanism study. This provides more explicit direction for further design of efficacious catalysts for H2O-involved reactions.