Heterogeneous Chemical Catalysis Research Articles

Enhanced water-induced effects enabled by alkali-stabilized Pd-OHx species for oxidation of benzyl alcohol

The water promotion effects, where water can provide a solution-mediated reaction pathway in various heterogeneous chemical catalysis, have been presented and attracted wide attention recently, yet, the rational design of catalysts with a certain ability of enhancing water-induced reaction process is full of challenges and difficulties. Here, we show that by incorporating alkali (Na, K) cations as an electronic and/or structural promoter into Pd/rGO-ZnCr2O4 (rGO, reduced graphene oxide), the obtained Pd(Na)/rGO-ZnCr2O4 as a representative example demonstrates an outstanding benzyl alcohol oxidation activity in the Pickering emulsion system in comparison to the alkali-free counterpart. The response experiments of water injection confirm the enhanced activity, and the Na-modified catalyst can further enhance the promotion effects of water on the reaction. The effects of alkali cations for Pd nanoparticles are identified and deciphered by a series of experimental characterizations (XPS, in situ CO-DRIFTS, and CO-TPR coupled with MS), showing that there is abundant −OH on the surface of the catalyst, which is stabilized by the formation of Pd−OHx. The alkali-stabilized Pd−OHx is helpful to enhance the water-induced reaction process. According to the results of in situ Raman as well as UV-vis absorption spectra, the Na-modulated Pd(Na)/rGO-ZnCr2O4 enables the beneficial characteristics for distorting the benzyl alcohol structure and enhancing the adsorption of benzyl alcohol. Further, the mechanism for enhanced water promotion effects is rationally proposed. The strategy of alkali cations-modified catalysts can provide a new direction to effectively enhance the chemical reaction involving small molecule water.

Heterogeneous strategies for selective conversion of lignocellulosic polysaccharides

Lignocellulosic biomass is the most abundant renewable carbon resource on earth, for which many efforts have been made to convert it using various chemocatalytic processes. Heterogeneously chemocatalytic conversion conducted based on reusable solid catalysts is the process with the greatest potential studied presently. This review provides insights into the representative achievements in the research area of heterogeneous chemical catalysis technologies for the production of value-added chemicals from lignocellulosic polysaccharides (cellulose and hemicellulose). Popular approaches for the conversion of lignocellulosic polysaccharides into chemicals, including hydrolyzation (glucose, xylose and arabinose), dehydration (5-hydroxymethylfurfuran, furfural, levulinic acid and lactic acid), hydrogenation/hydrogenolysis (sorbitol, mannitol, xylitol, 1,2-propylene glycol, ethlyene glycol and ethanol), selective oxidation (gluconic acid), have been comprehensively reviewed. However, technological barriers still exist, which have to be overcome to further integrate hydrolysis with the refinery processes based on multifunctional solid catalysts, and convert ligncellulosic polysaccharides into value-added fine chemicals. In general, the approaches and technologies are discussed and critically evaluated in terms of the possibilities and potential for further industrial implementation. Heterogeneously chemocatalytic conversions conducted over reusable solid catalysts are the major processes presently studied. Popular approaches to lignocellulosic polysaccharides (cellulose and hemicellulose) conversion to chemicals have been comprehensively reviewed.

Development of Green and Clean Processes for Perfumes and Flavors Using Heterogeneous Chemical Catalysis

Background: In this review, different heterogeneous catalysts based on acid, base, metal and enzymes are discussed for the synthesis of industrially relevant perfumes and flavor compounds. These molecules are mainly produced by a variety of reaction pathways such as esterification, isomerization, hydration, alkylation, hydrogenation, oxidation, etc. All these reactions are discussed thoroughly for the synthesis of vital aromatic compounds. The review also summarizes various recent technologies applied for designing new catalysts to obtain the maximum yield of the desired product. Overall, this review highlights the green, clean and eco-friendly processes which can be industrially accepted for the synthesis of perfumes, flavors and fragrances. Objective: The objective of the current review was to emphasize on the synthesis of industrially important perfumes and flavor molecules such as α-terpineol, cyclohexyl esters, thymol, raspberry ketone, etc. using heterogeneous catalysts. Results: Three hundred and eight papers are reported in this review, the majority of which are on heterogeneous catalysis for the synthesis of molecules which impart flavor or possess perfumery characteristics. Among all, the preparation of esters is highlighted as they represent an imperative functional group in aroma chemicals. Conclusion: The review confirms the need for heterogeneous catalysis in pollution-free and costeffective synthesis of flavor and perfumery compounds.

Manganese doped magnetic cobalt ferrite nanoparticles for dye degradation via a novel heterogeneous chemical catalysis

Composite cobalt ferrites doped with manganese were successfully synthesized via sol-gel auto combustion method and were annealed at a temperature of 400 °C. The catalytic activity of a series of catalysts at different manganese contents was studied using the sodium bisulfite-assisted system for degradation of water-soluble organic pollutants such as orange Ⅱ (OⅡ). The obtained ferrite compositions were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM) and X-ray photoelectron spectrometer (XPS). The results showed that the degradation efficiency was greatly enhanced in the presence of NaHSO3. In addition, all the Mn-containing samples showed much higher capability to degrade OⅡ than the pure CoFe2O4 under the same conditions. Among all the samples containing manganese, the CoMn0.2Fe1.8O4 sample showed higher degrading ability. The CoMn0.2Fe1.8O4 sample also showed strong ferromagnetic property with the saturation magnetization and remanence magnetization of 43.1 emu/g and 22.5 emu/g respectively, which is expected to provide a good magnetic separation performance.

Synthesis of eugenyl acetate through heterogeneous catalysis

ABSTRACTThis work aimed the production of eugenyl acetate through heterogeneous chemical catalysis of eugenol and acetic anhydride as substrates by commercial Lewatit ® GF 101 resin as catalyst. From the experimental design, the highest reaction conversion (94.85%) was obtained after 10 min of reaction time (1:1 substrates molar ratio, 1 wt% of catalyst content at 70°C), and up to 45 min a complete conversion was reached. The catalyst reuse was investigated, and after 10 reuse cycles, no loss of catalytic activity was observed. Antimicrobial activity of eugenyl acetate against Gram-positive (Staphylococcus aureus ATCC 9763, and Listeria monocytogenes ATCC 15117) and Gram-negative bacteria (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853) showed higher inhibition zone against to L. monocytogenes (42 mm). Besides, the eugenyl acetate antibacterial effect was also demonstrated by the minimum inhibitory concentration, and P. aeruginosa had higher inhibition (41.77 mm) at lower eugenyl acetate concentration (2500 μg.mL−1).

Fabrication of poly(ethylene glycol) particles with a micro-spherical morphology on polymeric fibers and its application in high flux water filtration

Abstract Polymeric coatings with micro-spherical morphology have a high surface area, which is advantageous for resins for heterogeneous chemical catalysis, for adsorption processes, nano-reactors, and anti-fouling coatings for water treatment membranes. The fabrication of stable, non-leachable micro-spherical polymers on solid surfaces is challenging. Here we introduce a straightforward method for fabricating polymeric particles with micro-spherical morphology on poly(ethylene terephthalate) fibers used as media for water filtration in microfiber technology. UV-initiated grafting with poly(ethylene glycol) methacrylate (PEGMA) monomers using benzophenone in aqueous solutions resulted in stable spherical particles coated on poly(ethylene terephthalate) threads, as revealed by FTIR, gravimetric degree of grafting, and SEM analyses. The micro-spherical morphology was unique to grafting with PEGMA monomers, whereas other types of methacrylate monomers resulted in smooth coatings. Grafting with PEGMA on high-flux water filtration cassette made of poly(ethylene terephthalate) fibers lead to enhanced performance and better dust removal capacity of the filter. The improved performance in coarse filtration is beneficial for treatment of water for agriculture, pretreatment facilities for freshwater supply, cooling water systems, and wastewater treatment. The protocol developed in this study is highly promising for both industrial and medical applications.

Asymmetric one-pot reactions using heterogeneous chemical catalysis: recent steps towards sustainable processes

Asymmetric one-pot reactions applying heterogeneous chemical catalysts and unifying the benefits of these catalytic materials with the advantages of one-pot methods, are surveyed.

Combination of Redox Assembly and Biomimetic Mineralization To Prepare Graphene-Based Composite Cellular Foams for Versatile Catalysis.

Graphene-based materials with hierarchical structures and multifunctionality have gained much interest in a variety of applications. Herein, we report a facile, yet universal approach to prepare graphene-based composite cellular foams (GCCFs) through combination of redox assembly and biomimetic mineralization enabled by cationic polymers. Specifically, cationic polymers (e.g., polyethyleneimine, lysozyme, etc.) could not only reduce and simultaneously assemble graphene oxide (GO) into cellular foams but also confer the cellular foams with mineralization-inducing capability, enabling the formation of inorganic nanoparticles (e.g., silica, titania, silver, etc.). The GCCFs show highly porous structure and appropriate structural stability, where nanoparticles are well distributed on the surface of the reduced GO. Through altering polymer/inorganic pairs, a series of GCCFs are synthesized, which exhibit much enhanced catalytic performance in enzyme catalysis, heterogeneous chemical catalysis, and photocatalysis compared to nanoparticulate catalysts.

Absolute Molecular Orientation of Isopropanol at Ceria (100) Surfaces: Insight into Catalytic Selectivity from the Interfacial Structure

The initial mechanistic steps underlying heterogeneous chemical catalysis can be described in a framework where the composition, structure, and orientation of molecules adsorbed to reactive interfaces are known. However, extracting this vital information is the limiting step in most cases due in part to challenges in probing the interfacial monolayer with enough chemical specificity to characterize the surface molecular constituents. These challenges are exacerbated at complex or spatially heterogeneous interfaces where competing processes and a distribution of local environments can uniquely drive chemistry. To address these limitations, this work presents a distinctive combination of materials synthesis, surface-specific optical experiments, and theory to probe and understand molecular structure at catalytic interfaces. Specifically, isopropanol was adsorbed to surfaces of the model CeO2 catalyst that were synthesized with only the (100) facet exposed. Vibrational sum-frequency generation was used to pr...

Graphitic carbon nitride nanosheets/sulfonated poly(ether ether ketone) nanocomposite membrane for direct methanol fuel cell application

As a novel kind of two-dimensional soft nanomaterial, graphitic carbon nitride (g-C3N4) has been boomingly explored in diverse fields such as photocatalysis and heterogeneous chemical catalysis, however, its potential application in proton exchange membranes (PEMs) fuel cells remains disclosed. In this study, nanocomposite membranes with varying g-C3N4 nanosheets content are fabricated by incorporating g-C3N4 nanosheets into sulfonated poly(ether ether ketone) (SPEEK). An increase in proton conductivity from 0.0606Scm−1 of the SPEEK control membrane to 0.0786Scm−1 of the nanocomposite membrane is achieved at the g-C3N4 nanosheets content of 0.5wt% at 20°C, stemming from that the improved connectivity of the ionic groups renders the acid-base pair effect and facilitates the Grotthuss-type transport of proton. Methanol permeability at room temperature decreases with the increase of the g-C3N4 nanosheets content, stemming from that the periodic vacancies in the lattice of g-C3N4 render the molecular sieving effect and the consequent high resistance for methanol permeation. An increase up to 39% in maximum power density is obtained, indicating the potential of g-C3N4 nanosheets for fuel cell application. Moreover, the superior mechanical properties of the g-C3N4 nanosheets lead to a 68% increase in ultimate tensile strength of the nanocomposite membranes (54.31MPa at the g-C3N4 nanosheets content of 0.5wt%).

Bridging the Chemical and Biological Catalysis Gap: Challenges and Outlooks for Producing Sustainable Chemicals

Recent advances in metabolic engineering have allowed for the production of a wide array of molecules via biocatalytic routes. The high selectivity of biocatalysis to remove functionality from biomass can be used to produce platform molecules that are suitable for subsequent upgrading over heterogeneous catalysts. Accordingly, the more robust continuous processing allowed by chemical catalysis could be leveraged to upgrade biologically derived platform molecules to produce direct or functional replacements for petroleum products. Herein, we highlight recent results that utilize a combination of chemical and biological catalysis, and using the perspective of heterogeneous chemical catalysis, we identify challenges that need to be addressed to bridge the gap between the two catalytic approaches. Specifically, studies are required to address the effects on catalyst performance of impurities that originate during bioprocessing. In addition, new generations of heterogeneous catalysts are required for stable op...