Preparation Of Heterogeneous Catalysts Research Articles

Green synthesis of ester base oil with high viscosity – Part Ⅰ: Catalyst preparation, characterization, evaluation, and mechanism analysis

High viscosity ester base oil, as an eco-friendly lubricant base oil with high performance, can significantly reduce the friction, wear, and energy consumption of large machinery. However, there is less research on the preparation of heterogeneous catalysts for synthesis of high viscosity ester oil. In this work, Sn/Zr mixed oxide catalysts were prepared for the green synthesis of ester base oil with high viscosity. This approach gets rid of additional template, surfactant, organic solvent, sulfur, nitrogen, phosphorus, and halogen, thereby avoiding the potential environmental pollution. A superior powdered catalyst MO-Sn8Zr-9.0-160-18 was developed with optimized Sn/Zr molar ratio, pH, hydrothermal temperature, and hydrothermal time of 8:1, 9.0, 160 °C, and 18 h, respectively. Results of catalyst characterization indicated that the developed catalysts were mesoporous materials with hydrophobic properties, allowing for free diffusion of macromolecules, adsorption of reactants, and desorption of water. Additionally, the specific surface area, pore volume, pore diameter, and surface hydrophobicity of catalyst were enhanced by doping Zr, so the catalysts with higher [Sn/Zr]ICP/[Sn/Zr]XPS exhibited better catalytic activity. Preformed catalyst was prepared by simple mechanical mixing method to achieve better catalyst separation. The specific surface area, acid amount, and acid strength of catalyst were indeed improved significantly after catalyst molding. By programmed heating, the preformed catalyst achieved a maximum carboxyl conversion of 97.2%. Moreover, spent catalyst could be reactivated via solvent washing, drying, calcination, and hydrogen reduction, exhibiting good reusability.

Microwaves and Heterogeneous Catalysis: A Review on Selected Catalytic Processes

Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO2) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts.

Reduction of NO by CO catalyzed by Fe-oxide/Al2O3: Strong catalyst-support interaction for enhanced catalytic activity

Fe-oxide/Al2O3 catalysts were fabricated by depositing Fe-oxide nanoparticles with a lateral size less than ~2 nm in a highly dispersed manner within mesoporous Al2O3 using temperature-regulated chemical vapor deposition (TRCVD). The Fe-oxide/Al2O3 catalysts were post-annealed at either 450 °C (for 2 h) or 750 °C (for 2 or 8 h) and were used to catalyze NO reduction by CO. Catalytic activity was significantly enhanced with increased annealing temperature and time. Secondary ion mass spectrometry using Bi3+ as the primary ion shows an increase in the FeAlO+ signal from the interfaces between Fe-oxide and Al2O3 with increasing annealing temperature and time, suggesting that the enhanced interaction between Al2O3 and Fe-oxide is responsible for the increased catalytic activity. It is shown that TRCVD with a proper post-annealing step is a competitive tool for preparation of heterogeneous catalysts with highly dispersed catalyst nanostructures within mesoporous substrates that contain rich oxide/oxide interfaces and allow enhanced catalytic activity.

Design, characterization and catalytic evaluation of halometallic ionic liquid incorporated Nd2O3 nanoparticles ([smim][FeCl4]-@Nd2O3) for the synthesis of N-aryl indeno pyrrole derivatives.

Silica modified imidazolium [smim] based halometallic ionic liquids, [smim][MCl4] (M = Fe, Cu and Zn), were synthesized for the evaluation of acidic and catalytic properties. Among these ILs, [smim][FeCl4]− was used for the preparation of heterogeneous catalyst ([smim][FeCl4]−@Nd2O3) by simple immobilization of IL on Nd2O3 nanoparticles. The structure of [smim][FeCl4]−@Nd2O3 was established by various techniques including FTIR, Raman, UV-vis DRS, powder XRD, SEM/EDX, elemental mapping, TEM, TGA, EPR and XPS analyses. The stability of nano-catalyst, [smim][ FeCl4]−@Nd2O3, was established with the help of zeta potential analysis which showed a value of −40.32 mV lying under the stability range. Potentiometric titration with n-butyl amine was used to evaluate the acidic properties of [smim][MCl4] as well as [smim][FeCl4]−@Nd2O3. The catalytic potential of the material was probed through the one pot synthesis of N-aryl indeno pyrrole derivatives. The results showed excellent performance of the material by producing a high yield (98%) of indeno pyrrole derivatives. A recyclability experiment revealed that the catalyst was efficient in up to five cycles with insignificant loss in catalytic activity. The evaluation of green metrics indicated the sustainability of the present protocol in terms of high atom economy and low E-factor.

Utilizing Sabang sea urchin shell as an inexpensive and alternative heterogeneous catalyst for biodiesel synthesis

This research is focused on the utilization of sea urchin shells collected from Sabang island, Aceh, Indonesia as raw material for heterogeneous catalyst preparation and Its catalytic study on transesterification reaction of palm oil and methanol to produce fatty acid methyl esters which referred as biodiesel compound. The catalyst was prepared through thermal decomposition method, namely, it was calcined at 900°C in air atmosphere for 4 h and modified with various concentration of potassium element (5, 10, and 20wt.%) as dopant substance using impregnation process. The characterization results using X-Ray Diffraction (XRD) proved that the produced catalyst was dominated by CaO crystals, in which MgO was detected as a minor compound. Another characterization using Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) showed that the produced catalyst has been homogeneous formation on their morphology. Finally, in order to have scientific information regarding its catalytic activity, the prepared catalyst was successfully applied to the transesterification reaction of palm oil and methanol resulting in ricinoleic methyl esters as the main biodiesel product.

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry.

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.

Evaluation of the synthesis routes for the preparation of heterogeneous catalysts obtained from coconut shell and its application in the biodiesel production

Evaluation of the synthesis routes for the preparation of heterogeneous catalysts obtained from coconut shell and its application in the biodiesel production

Synthesis of γ-Al2O3–supported Pt nanoparticles using Al-based metal-organic framework as medium and their catalytic performance for total propene oxidation and selective nitrobenzene hydrogenation

The control of the shape and dispersibility of Pt nanoparticles (NPs) supported on Al2O3 is challenging. To address this issue, the use of metal-organic frameworks as a template for the preparation of heterogeneous catalysts is a promising methodology. Herein, we used an Al-based metal-organic framework as a medium to synthesize uniform Pt NPs supported on γ-Al2O3 (Pt@γ-Al2O3) in the absence of protective and capping agents and subjected these nanoparticles to instrumental analyses. Microscopic imaging indicated that nanoparticles had diameters of 2–5 nm (mean = 3.4 nm) and revealed the formation of Pt nanocubes on the alumina surface. Pt@γ-Al2O3 exhibited excellent catalytic activity for propene oxidation and displayed long-term stability, with the corresponding activation energy determined as 63.9 kJ mol−1. Moreover, Pt@γ-Al2O3 also effectively catalyzed the gas-phase hydrogenation of nitrobenzene to aniline at 100 °C, achieving a turnover frequency of 565 h−1 and a selectivity of >90%. Thus, the obtained results contribute to the further development of supported heterogeneous catalysts from metal-organic frameworks as precursors and media.

Development of heterogeneous catalyst from chicken bone and catalytic testing for biodiesel with simultaneous processing

The objective of this research is to preparation of heterogeneous catalyst from chicken bone. The catalyst was testing for biodiesel production from used cooking oil. Preparation of heterogeneous catalyst by using chemical and thermal treatment. The catalyst was characterized by morphology analysis and specific surface area. The catalytic testing was used simultaneous reaction of esterification-transesterification. The solids product of chicken bone was contained CaO composition of 42.25%. The catalyst was impregnated with FeCl3. The results of catalyst characterization were about composition of CaO of 25.60%, FeO of 1.16% and obtained surface area 32.546 m2 / g, total pore volume of 0.051 cc / g, average pore radius of 16.150 Å. The performance testing of heterogeneous catalyst was can used in biodiesel production with simultaneous reaction. In esterification and trans esterification, methyl ester can be obtained in biodiesel product. The biodiesel production conducted at mole ratio of methanol to used cooking oil 6: 1, 3% (w/w) of catalyst to cooking oil, and reaction time of 3 hours, with 22% biodiesel yield.

Low-temperature hydrogenation of dimethyl oxalate to ethylene glycol via ternary synergistic catalysis of Cu and acid−base sites

Metal-support synergistic catalysis plays a crucial role in heterogeneous reaction processes from viewpoint of both fundamental research and practical applications. Herein, a series of Cu-based nanocatalysts were prepared by virtue of topotactic structure transformation from CuMgAl-layered double hydroxide (CuMgAl − LDH) precursors. Various in situ investigations including XRD, XPS, EXAFS and FTIR demonstrate that the structural transformation of CuMgAl − LDH results in well-dispersed Cu nanoparticles (metallic Cu° as the single species) supported on mixed metal oxides (MgO and Al2O3, denoted as Cu/MMO). The optimal catalyst (Cu/MMO−S3) exhibits an excellent catalytic performance toward hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) (yield: 94.4%) at an exceptionally low operation temperature (438 K). This is, to the best of our knowledge, at least 30―40 K lower than normally accepted temperature for Cu-based catalysts (above 473 K). Structure − property correlation investigations were performed via in situ FTIR, N2O pulse chemisorption, NH3−TPD and CO2−TPD, and the results revealed that a ternary synergistic catalysis of Cu and acid − base sites makes a predominant contribution: Lewis acid sites (Al3+) and medium-strong basic sites (Mg2+−O2− pair) of supports serve as active sites for adsorption of polarized CO/CO group in DMO molecule; while H2 undergoes dissociation adsorption on Cu° site. This precise control over metal and acid − base sites based on LDHs precursor approach would lead to new possibilities in rational design and preparation of heterogeneous catalysts for hydrogenation of CO/CO group.

Colloidal Nanocrystals as Building Blocks for Well-Defined Heterogeneous Catalysts

The goal of this perspective is to highlight the use of colloidal nanocrystals in the preparation of heterogeneous catalysts of well-defined structures with the objective to advance catalytic science. Colloidal nanocrystals are prepared with control over size, shape, and composition and are used as precursors to provide supported systems of interest in different areas of catalysis. Advances in the preparation of this class of catalysts are discussed, as well as their use to understand the effect of size, shape, composition, and support chemistry in catalyzed reactions. The use of these materials for microscopy and spectroscopy studies, especially in the investigation of structural changes that occur to catalytic materials, is also highlighted. Finally, challenges and opportunities in the field are discussed to underline prospects and limitations of this approach. It is expected that this area will grow in interest in the future and that these materials will help elucidate several aspects of catalytic science through a systematic approach introduced by using controlled colloidal nanocrystals.

Simultaneous Catalytic Conversion of C6 and C5 Sugars to Methyl Lactate in Near-critical Methanol with Metal Chlorides

Cellulose and hemicellulose make up roughly two-thirds of lignocellulose. Currently, research is mainly focused on converting them to different chemicals, which causes low utilization rates and high separation costs. In this work, the simultaneous conversion of C6 and C5 sugars from cellulose and hemicellulose to methyl lactate in near-critical methanol with 15 different types of metal chlorides was studied. The trends of the catalytic conversions of C6 and C5 sugars with different metal chlorides were similar. Methyl lactate yield initially increased and then decreased steadily with an increase in the pKa value of the metal ions, which suggested that medium Lewis acidity was favorable for the production of methyl lactate. A possible reaction mechanism was proposed. The results will provide direction for the preparation of heterogeneous catalysts for simultaneously converting cellulose and hemicellulose to methyl lactate.

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4-Nitrophenol in Solution.

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation.

Innovative Sol-Gel Routes for the Bottom-Up Preparation of Heterogeneous Catalysts.

Heterogeneous catalysts can be prepared by different methods offering various levels of control on the final properties of the solid. In this account, we exemplify bottom-up preparation routes that are based on the sol-gel chemistry and allow to tailor some decisive properties of solid catalysts. First, an emulsion templating strategy is shown to lead to macrocellular self-standing monoliths with a macroscopic 3D structure. The latter can be used as catalyst or catalyst supports in flow chemistry, without requiring any subsequent shaping step. Second, the aerosol-assisted sol-gel process allows for the one-step and continuous production of porous mixed oxides. Tailored textural properties can be obtained together with an excellent control on composition and homogeneity. Third, the application of non-hydrolytic sol-gel routes, in the absence of water, leads to mixed oxides with outstanding textural properties and with peculiar surface chemistry. In all cases, the resulting catalytic performance can be correlated with the specificities of the preparation routes presented. This is exemplified in catalytic reactions in the fields of biomass conversion, petro chemistry, enantioselective organic synthesis, and air pollution mitigation.

Selective Fe Promotion on Au Nanoparticles: An Efficient Way to Activate Au/SiO2 Catalysts for the CO Oxidation Reaction

AbstractThe fabrication of the metal–metal oxide interface for the design and preparation of heterogeneous catalysts has been widely considered. In this work, a simple, aqueous‐phase Fe promotion strategy was studied on an inactive Au/SiO2 model catalyst to generate an active Au–FeOx interface for the CO oxidation. We found that the addition of either Fe2+ or Fe3+ led to significantly higher activity if the Au NPs were already deposited on the SiO2 compared to a prepromotion of the bare support. Combining X‐ray diffraction, elemental analysis, transmission electron microscopy and energy dispersive X‐ray spectroscopy characterizations with the CO oxidation tests, we proved that the postpromotion strategy could more efficiently fabricate the Au‐Fe interface, which after a proper thermal pretreatment could transform to the catalytically active Au–FeOx interface. The formation of such Au–Fe species interface was ascribed to the selective accumulation of the Fe3+ hydrolysis products on the Au nanoparticles (NPs), driven both by a heterogeneous nucleation/growth mechanism and a direct electrostatic adsorption mechanism.

Three‐dimensional Printing for Catalytic Applications: Current Status and Perspectives

Three‐dimensional (3D) printing, also known as additive manufacturing, is a fabrication method that has recently received worldwide attention. It provides a convenient and economical way to prepare 3D structures in designable ways. As the technology has developed and the operational costs have decreased, the applications of 3D printing have greatly expanded. Catalyst fabrication is a promising area for 3D printing. Printing processes result in better control of catalyst structures and catalyst distribution. In this perspective, a general overview of the commonly available 3D printing methods that are feasible for the preparation of heterogeneous catalysts is given. Additionally, recent works on printing strategies and new materials for catalysts are discussed. Future development is also addressed.

Discrete element method simulations and experiments of dry catalyst impregnation for spherical and cylindrical particles in a double cone blender

The dry impregnation of catalyst supports is a widely used process in the preparation of heterogeneous catalysts, however there has not been a lot of work done computationally on this process. In this work, discrete element method (DEM) simulations coupled with an algorithm for the transfer of fluid to and between particles are used to study dry impregnation. We use a previously developed model, which has been further validated with geometrically equivalent experiments and the results show very good agreement. The effects of rotational speed, particle size and particle morphology are explored in order to achieve the best overall mixing and fluid content uniformity in the particle bed. We study spheres and cylinders of different sizes and aspect ratios. Axial mixing analysis and liquid distributions are used to investigate the propagation of the fluid throughout the particle bed with the goal of understanding the effect of operational and material parameters and ultimately to improve fluid content uniformity in systems with particles of different morphologies. The fluid content uniformity is characterized by the relative standard deviation (RSD) of the liquid content from all the particles in the system. Our results show that cylinders always take less time to mix than spheres of the same diameter and mixing times are also shorter for cylinders of higher aspect ratios when compared to cylinders of smaller aspect ratio. Likewise, the times to reach good fluid content uniformity are shorter for cylinders with higher aspect ratios as compared with cylinders with lower aspect ratios. We also observe that mixing time in the axial direction for both spheres and cylinders followed an exponential function of the surface area to volume ratio. We found a linear correlation between the times to achieve good axial mixing and the times to achieve good fluid content uniformity in the entire particle bed, which suggests that mixing in the axial direction controls fluid uniformity in the entire particle bed.

Ferrocene as an efficient and recyclable heterogeneous catalyst for catalytic ozonation in water

Heterogeneous catalytic ozonation is a promising technique to improve ozonation for degrading organic contaminants. Preparation of heterogeneous catalysts (e.g., substrate-supported metals and metal oxides) for ozonation typically involves multiple steps and reagents. Because iron (Fe) is an abundant and non-noble metal, Fe-based heterogeneous catalysts are attractive for ozonation. Therefore, it is critical to develop a readily-available, stable and non-toxic Fe-based heterogeneous catalyst. To this end, we propose ferrocene (Fc), consisting of two cyclopentadienyl rings bound on opposite sides of a central Fe2+ atom, as a catalyst for ozonation. Degradation of the toxic dye amaranth was employed as a model test. The presence of Fc significantly improved amaranth degradation extent and kinetics, and Fc did not adsorb amaranth in water. Factors influencing amaranth degradation were investigated including Fc and ozone dosages, temperature, pH, and addition of NaCl and humic acid. Effects of radical inhibitors were also examined to provide insights into the occurrence of radical species during Fc-catalyzed ozonation. Degradation of amaranth was primarily attributed to derivative reactive oxygen species, as well as direct degradation by ozone to a lesser extent. A pathway of amaranth degradation is proposed based on degradation intermediates detected using LC/MS/MS. Fc was also re-used over multiple cycles for catalyzing ozonation to degrade amaranth without a loss of efficiency. These results indicate that Fc is a promising commercially available nanoscale heterogeneous catalyst for catalytic ozonation.

Production and Characterization of Heterogeneous Catalyst (CaO) from Snail Shell for Biodiesel Production Using Waste Cooking Oil

The waste snail shell was screened to determine its efficiency as heterogeneous catalyst for biodiesel production via trans-esterification reaction. Prior to its use, the solid oxide material (shell) was calcined at 800°C for 4 h to convert CaCO3 to CaO. Physicochemical analysis of waste cooking oil reveals the acid value (3.47 mg KOH/gm), density (0.9 g/cm3), moisture content (0.1%) and kinematic viscosity (42.2) respectively. The prepared solid oxide catalyst was characterized using X-ray Fluorescence (XRF) and Fourier Transform Infrared Spectroscopy (FT-IR) methods. The catalytic activity of the catalyst was evaluated by the transesterification reaction under the following reaction conditions: temperature (60°C), time (3 h) and methanol to oil ratio (9:1) respectively. GC-MS analysis was used to characterize the fatty acid methyl ester composition. The research signified successful application of waste snail shell as heterogeneous catalyst for prospective economic preparation of heterogeneous catalyst. It also developed an unconditional avenue for using the waste snail shell as the catalyst.

Mixed metal oxides from sucrose and cornstarch templated hydrotalcite-like LDHs as catalysts for ethyl biodiesel synthesis

Sucrose and cornstarch were used as organic templates in the synthesis of hydrotalcite-like layered double hydroxides (LDHs) prepared by the coprecipitation with partial replacement of Mg by Zn, and Al by Fe. Non-template materials were taken as references. All LDHs were used as precursors of mixed metal oxides (MMOs) by calcination and applied as catalysts for ethyl biodiesel synthesis via transesterification reactions of soybean oil and ethanol. The LDHs were characterized by XRD, TG, FTIR-ATR and the respective MMOs by SEM, BET, basicity and acidity. Crystallographic data from templated LDHs showed lower crystallinity compared to the reference homologous materials, and it was observed that cornstarch decreases the average surface areas (from 173 to 94m2g−1) and the size of the crystallites (from 147 to 92Å). FTIR spectra indicated carbohydrates were occluded inside the crystals. While this did not influence the number of acidic sites on the MMOs, it enhances the alkaline sites. Under the catalytic conditions of this experiment, cornstarch templated MMOs reach an average ethyl biodiesel conversion of 70% whereas those prepared with sucrose 45%, and the homologous reference materials only 36%. These results demonstrated the great potential of using carbohydrates as biotemplates in the preparation of heterogeneous catalysts for transesterification reactions.