Combined Catalysis Research Articles

The catalytic kinetics and cfd simulation of multi-stage combined removal of acrylonitrile tail gas

There is no kinetic data and rate equation that can be used directly for catalytic combustion of acrylonitrile tail gas, which leads to the multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal. In the actual application process, affected by the internal and external diffusion, this paper proposes the multi-stage combined catalytic kinetic research and CFD simulation analysis of acrylonitrile tail gas collaborative removal. Based on the judgment of multi-stage combined catalytic reaction rules of acrylonitrile tail gas collaborative removal, the multi-stage combined catalytic reaction network of acrylonitrile tail gas collaborative removal is solved by matrix transformation. The possible reaction path in the multi-stage combined catalytic reaction network of acrylonitrile tail gas collaborative removal is solved. For quantitative calculation of product distribution, each step of reaction parameters and dynamic factors are required. According to the mechanism of positive carbon ion reaction, materials were used Studio software and genetic algorithm are used to calculate the dynamic factors and determine the dynamic parameters; the grid automatic generator AutoGrid5 embedded in the Fine/TurboTM software package is used to generate the CFD simulation network, and the iterative algorithm is used to calculate the limit value of the CFD simulation; the S-A model in the CFD simulation platform is used to get the modified value of the dynamic mathematical model, and the dynamic factors and parameters are brought into it to establish the CA mathematical model of multi-stage combined catalytic kinetics for the CO removal of olefine and nitrile tail gas. The experimental results show that, under the same experimental device and parameters, the internal and external diffusion effects of the multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal are detected. The multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal in this study uses 10-20 mesh catalyst, and the retention time of acrylonitrile tail gas is less than 4.62 s, the internal and external diffusion will not affect the acrylonitrile tail gas collaborative removal The practical application of the kinetic model for the removal of multi-stage combined catalysis.

The role of the ceria dopant on Ni / doped-ceria anodic layer cermets for direct ethanol solid oxide fuel cell

The effect of ceria dopant aiming at stability in Ni/doped-ceria anodic layers for direct ethanol solid oxide fuel cells (SOFC) was studied. Solid solutions of ceria doped with Y, Gd, Zr, or Nb (10 mol%) impregnated with NiO were tested in a fixed bed reactor for ethanol conversion reactions and for direct (dry) ethanol SOFC. The ceria dopant showed a marked effect on both the catalytic and the electrical transport properties of the ceramic support. Catalytic activity data revealed that the studied materials deactivate in ethanol decomposition reaction but are stable for ethanol steam reforming. Thus, feeding dry ethanol to the SOFC with a Ni/doped-ceria anodic catalytic layer evidenced that water produced from the electrochemical hydrogen oxidation provides steam for the internal reforming resulting in great stability of the fuel cells tested during ~100 h. The combined catalysis and SOFC results demonstrate Ni/doped-ceria is as candidate anode layer for stable SOFC running on bioethanol.

Synthesis of two new lipid mediators from docosahexaenoic acid by combinatorial catalysis involving enzymatic and chemical reaction

Omega-3 polyunsaturated fatty acids (PUFAs) have been known to have beneficial effects in the prevention of various diseases. Recently, it was identified that the bioactivities of omega-3 are related to lipid mediators, called pro-resolving lipid mediators (SPMs), converted from PUFAs, so they have attracted much attention as potential pharmaceutical targets. Here, we aimed to build an efficient production system composed of enzymatic and chemical catalysis that converts docosahexaenoic acid (DHA) into lipid mediators. The cyanobacterial lipoxygenase, named Osc-LOX, was identified and characterized, and the binding poses of enzyme and substrates were predicted by ligand docking simulation. DHA was converted into three lipid mediators, a 17S-hydroxy-DHA, a 7S,17S-dihydroxy-DHA (RvD5), and a 7S,15R-dihydroxy-16S,17S-epoxy-DPA (new type), by an enzymatic reaction and deoxygenation. Also, two lipid mediators, 7S,15R,16S,17S-tetrahydroxy-DPA (new type) and 7S,16R,17S-trihydroxy-DHA (RvD2), were generated from 7S,15R-dihydroxy-16S,17S-epoxy-DPA by a chemical reaction. Our study suggests that discovering new enzymes that have not been functionally characterized would be a powerful strategy for producing various lipid mediators. Also, this combination catalysis approach including biological and chemical reactions could be an effective production system for the manufacturing lipid mediators.

An alternative pentose phosphate pathway in human gut bacteria for the degradation of C5 sugars in dietary fibers.

The microbial degradation of pentoses in the human gut is a crucial factor for the utilization of plant-based dietary fibers. A vast majority of gut microbes are able to use these C5-sugars as a carbon and energy source. However, the underlying metabolic pathways are not fully understood. Bioinformatic analysis showed that a large number of abundant gut bacteria lack genes encoding a transaldolase as a key enzyme of the pentose phosphate pathway. Among them was the important human gut microbe Prevotellacopri, which was able to grow in minimal media containing xylose or hemicelluloses as the sole carbon source. Therefore, we looked for an alternative pathway for pentose conversion in P.copri using bioinformatics, enzyme activity assays, and the detection of intermediates of pentose metabolism. It became evident that the organism converted C5-sugars via the sedoheptulose-1,7-bisphosphate pathway (SBPP) to connect pentose metabolism with glycolysis. To circumvent the transaldolase reaction, P.copri uses the combined catalysis of a pyrophosphate-dependent phosphofructokinase and a fructose-bisphosphate aldolase. Furthermore, we present strong evidence that the SBPP is widely distributed in important gut bacteria, including members of the phyla Bacteroides, Firmicutes, Proteobacteria, Verrucomicrobia, and Lentisphaerae.

Enhanced xylan conversion to xylitol in a bio- and chemocatalytic one-pot process

A novel hybrid process for the conversion of xylan via hydrolytic hydrogenation achieved a xylitol yield of up to 65 %. As part of this study, the hypothesis of decreased product (xylose) inhibition of enzymes during xylan hydrolysis due to rapid conversion of xylose to xylitol was investigated experimentally. We found that xylose inhibition can play an important part in the reaction kinetics of xylan hydrolysis with commercially available enzymes. For example, at 10 wt.-% xylose concentration, the activity of enzymes dropped by ca. 80 %. In contrast, the final desired product xylitol showed only a slight inhibitory effect of about 20 % activity loss of the enzymes.The one-pot process of hydrolytic hydrogenation requires enzyme stability at higher-than-optimal temperatures and pressures, to ensure their activity at harsher process conditions needed for the chemo-catalytic hydrogenation. Therefore enzyme activity was tested at elevated temperatures and pressures. The tests were carried out with two enzyme mixtures (Ecopulp TX-800 A and Alkozym CPX). Both showed no activity loss over 60 min exposure time at pressures of up to 40 bar. However, their thermal resistance differs strongly, with Alkozym already deactivating at 50 °C, while Ecopulp remained mostly active at up to 80 °C.The novel sequential process (4 consecutive steps) achieved a xylitol yield of up to 65 % with almost 80 % xylan conversion.Our findings show both limitations and potential benefits of hybrid processes which try to exploit both biological and chemical catalysis. This type of combined catalysis for reaction cascades could further accelerate the ongoing research in process development for catalytic biorefineries.

Designing Multi-Dopant Species in Microporous Architectures to Probe Reaction Pathways in Solid-Acid Catalysis.

The introduction of two distinct dopants in a microporous zeotype framework can lead to the formation of isolated, or complementary catalytically active sites. Careful selection of dopants and framework topology can facilitate enhancements in catalysts efficiency in a range of reaction pathways, leading to the use of sustainable precursors (bioethanol) for plastic production. In this work we describe our unique synthetic design procedure for creating a multi-dopant solid-acid catalyst (MgSiAPO-34), designed to improve and contrast with the performance of SiAPO-34 (mono-dopant analog), for the dehydration of ethanol to ethylene. We employ a range of characterization techniques to explore the influence of magnesium substitution, with specific attention to the acidity of the framework. Through a combined catalysis, kinetic analysis and computational fluid dynamics (CFD) study we explore the reaction pathway of the system, with emphasis on the improvements facilitated by the multi-dopant MgSiAPO-34 species. The experimental data supports the validation of the CFD results across a range of operating conditions; both of which supports our hypothesis that the presence of the multi-dopant solid acid centers enhances the catalytic performance. Furthermore, the development of a robust computational model, capable of exploring chemical catalytic flows within a reactor system, affords further avenues for enhancing reactor engineering and process optimisation, toward improved ethylene yields, under mild conditions.

Monitoring, assessment, and prediction of microbial shifts in coupled catalysis and biodegradation of 1,4-dioxane and co-contaminants

Microbial community dynamics were characterized following combined catalysis and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Although a few specific bacterial taxa are capable of removing 1,4-dioxane and individual CVOCs, many microorganisms are inhibited when these contaminants are present in mixtures. Chemical catalysis by tungstated zirconia (WOx/ZrO2) and hydrogen peroxide (H2O2) as a non-selective treatment was designed to achieve nearly 20% 1,4-dioxane and over 60% trichloroethene and 50% dichloroethene removals. Post-catalysis, bioaugmentation with 1,4-dioxane metabolizing bacterial strain,Pseudonocardia dioxanivorans CB1190, removed the remaining 1,4-dioxane. The evolution of the microbial community under different conditions was time-dependent but relatively independent of the concentrations of contaminants. The compositions of microbiomes tended to be similar regardless of complex contaminant mixtures during the biodegradation phase, indicating a r-K strategy transition attributed to the shock experienced during catalysis and the subsequent incubation. The originally dominant genera Pseudomonas and Ralstonia were sensitive to catalytic oxidation, and were overwhelmed by Sphingomonas, Rhodococcus, and other catalyst-tolerant microbes, but microbes capable of biodegradation of organics thrived during the incubation. Methane metabolism, chloroalkane-, and chloroalkene degradation pathways appeared to be responsible for CVOC degradation, based on the identifications of haloacetate dehalogenases, 2-haloacid dehalogenases, and cytochrome P450 family. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase that were in line with shifting predominant genera, confirming the deterministic processes guiding the microbial assembly. Collectively, this study demonstrated that catalysis followed by bioaugmentation is an effective treatment for 1,4-dioxane in the presence of high CVOC concentrations, and it enhanced our understanding of microbial ecological impacts resulting from abiotic-biological treatment trains. These results will be valuable for predicting treatment synergies that lead to cost savings and improve remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

A bifunctional nanoplatform based on copper manganate nanoflakes for bacterial elimination via a catalytic and photothermal synergistic effect.

Bacterial infection has been recognized as one of the greatest threats to public health. In view of the continuous increase of bacterial resistance, constructing a collaborative bactericidal platform is a promising strategy to enhance the efficiency of antimicrobial agents. Herein, we report a facile, biocompatible and versatile nano-platform based on positively charged copper manganate nanoflakes (CuMnO2 NFs), which exhibits intrinsic peroxidase-like catalytic activity and excellent photothermal properties. The CuMnO2 NFs can bind with negatively charged bacteria via electrostatic interactions, and generate hydroxyl radicals (˙OH) through catalysis involving hydrogen peroxide (H2O2) to make bacteria more susceptible to temperature. Introducing near-infrared light generates hyperthermia to fight against bacteria and enhances the peroxidase-like catalytic activity of the CuMnO2 NFs, thus producing more ˙OH to combat bacteria. The PTT-enhanced ˙OH synergistic antibacterial strategy exerts desirable antibacterial efficiencies of 98.78% and 99.92% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) at a controlled low temperature (below 50 °C), without damage to healthy tissues. Animal experiments indicate that this synergistic treatment has a better therapeutic effect on S. aureus-infected wounds in mice, compared with either treatment by itself. Therefore, this work holds great promise for developing new synergistic antimicrobial strategies to treat bacterial infections.

Sustainable and Affordable Chemistry

AbstractThe Special Issue on Sustainable and Affordable Chemistry to Meet Future Challenges in the Pharmaceutical Industry illustrates the hopes within the field of catalysis. With spectacular reports based on transition‐metal catalysis, biocatalysis, photoredox catalysis, organocatalysis, hybrid, or combined catalysis, utilizing sustainable media especially chemistry in water and flow chemistry, we hope to inspire others to join the quest for a more sustainable future.

Pd-Colloids-Catalyzed/Ag2 O-Oxidized General and Selective Esterification of Benzylic Alcohols.

Palladium colloids obtained from the degradation of Hermann-Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative-esterification successfully.

Effects of minerals containing sodium, calcium, and iron on oxy-fuel combustion reactivity and kinetics of Zhundong coal via synthetic coal

The greatly high contents of alkali and alkali earth metals in Zhundong coal have a negative impact on the combustion and utilization of the coal, which results in serious fouling and slagging problems. In the present study, the influences of different minerals on the oxy-fuel combustion of Zhundong coal via synthetic coal were investigated by thermal analysis, and two isoconversional methods were applied to conduct the kinetic analysis. Additive minerals with single metallic elements including sodium (NaCl, NaCO3, NaAlSi3O8), calcium (CaCl2, CaCO3, CaSO4), and iron (Fe2O3, Fe3O4 and FeS2) rather than complex mixtures were added into synthetic coal to avoid the combined catalysis among various minerals. The experimental results show that the thermogravimetric and derivative thermogravimetric curves of synthetic coals under oxy-fuel conditions are similar to those of Zhundong coals. Most of selected additive minerals affect the ignition temperature slightly (less than 10 °C) but tend to lower the burnout temperature (5–25 °C), which narrows the main combustion temperature zone. The addition of CaCl2 raises the burnout temperature from 645.4 to 689.5 °C and drives down the average combustion rate from 4.44 to 3.83% min−1, while other minerals exhibit negative correlation with the maximum and average combustion rates in most cases. The reaction kinetics analysis indicates that the apparent activation energy of coal combustion depends heavily on the category of additive minerals, which varies from 21.31 to 39.05 kJ mol−1 (average values calculated by KAS method). Besides, the apparent activation energy declines with an increase in the conversion rate of samples.

The carbonization of polymers: basic problems and applications

The key issue to promote the carbonization of polymeric materials is how to adjust the degradation products of polymers and control the carbonization of these products. The carbonization of polymers supplies a new strategy to prepare polymer materials with enhanced flame retardancy and provides a new way to convert waste polymeric materials into nanocarbon materials. This short review focused on the progress of the carbonization of polymeric materials in recent years in connection with those solved by our research group. We introduced three carbonization strategies, that is, “combined catalysis”, “templating carbonization” and “fast carbonization”, as well as the influencing factors of polymer carbonization and its mechanism. We also highlighted the application of polymer carbonization in improving the flame retardancy of polymer materials and preparation of carbon materials, and discussed utilizations of the resultant carbon materials in the environment remediation, energy storage, catalysis, and gas adsorption. The development prospect of polymer carbonization was also included.

Copper- and Borinic Acid-catalyzed Propargylic Etherification of Propargylic Carbonates with Benzyl Alcohols

Propargylic substitution reactions have offered useful synthetic methods because further transformations based on the alkyne moiety in the propargylic substituted products was readily achieved to construct more complex organic compounds. A large number of works have been devoted to enantioselective propargylic substitution reactions with a variety of nucleophiles. However, successful examples of the use of alcohols as nucleophiles have been quite limited until now. To achieve utilization of aliphatic alcohols, herein we report the use of combined catalysis of a copper-pybox complex and a borinic acid. In this catalytic system, aliphatic alcohols such as benzyl alcohol derivatives were successfully applied to afford the corresponding propargylic etherified products in good yields with high enantioselectivities.

Glucose isomerization catalyzed by bone char and the selective production of 5-hydroxymethylfurfural in aqueous media

Glucose isomerization and selective production of 5-hydroxymethylfurfural in aqueous media, using combined catalysis of bone char and acidic ionic liquid.

P4VP-RuII(bda) polyelectrolyte-metal complex as water oxidation catalyst: on the unique slow-diffusion and multi-charge effects of the polyelectrolyte ligand.

In this work, we analyze the catalytic mechanism of P4VP–RuII(bda) polyelectrolyte–metal complex (PMC) as a water oxidation catalyst and elucidate how the unique slow diffusion and multi-charge properties of the polyelectrolyte ligand dominate the catalytic process. Four poly(4-vinyl pyridine)–Ru(bda) (P4VP–Ru) PMCs with different chain lengths and controlled Ru loading amounts were prepared and used as catalysts for catalytic water oxidation. These catalysts present excellent catalytic performance with turnover numbers (TON) from ∼1200 to ∼1700 because of the good hydration properties. Surprisingly, the combined catalysis kinetics and kinetic isotope effect (KIE) studies for P4VP–Ru PMCs confirm the single-site water nucleophilic attack (WNA) mechanism in catalysis, rather than the interaction between two metal oxide units (I2M). A combination of dynamic light scattering characterization, zeta-potential measurement and molecular dynamics simulation reveals that the slow diffusion and multi-charge properties of the polyelectrolyte ligand are responsible for the observed mechanism difference between the P4VP–Ru PMC system and small-molecule multi-nuclear system, though the two systems actually own a similar structural feature (flexible linkages between Ru centers). Our experimental and simulation results highlight the fact that though the existence of flexible linkages between Ru centers could provide large conformation entropy for the occurrence of Ru-dimerization in small-molecule and neutral polymer systems, the entropy elasticity could not overcome the electrostatic interaction energy in the PMC system. Clearly, this work unambiguously clarified why both intra-chain and inter-chain Ru-dimerization (I2M) are prohibited for the PMC system from a perspective of macromolecular chemistry and physics.

Mild Upgrading of Bio-Crude Pyrolysis Oil: A Concept Based on Bio-Based Alcohols with Selective Water Adsorption

Biocrude pyrolysis oil is obtained by a process called fast-pyrolysis, in which almost any organic-based feedstock is thermally processed at moderate temperatures, in the range of 400–600 °C, in the absence of oxygen at short residence times. After condensing the vapors in a cooling tray, a dark-brown bioliquid is obtained. The quality of the thus obtained fast pyrolysis oil has some barriers for its direct use as transportation fuel. Low caloric value, high viscosity, and corrosion are the major challenges for its implementation in conventional engines. There have been sustained efforts to improve the quality of the oil. In this Communication we are reporting a concept on improving the acidic properties by means of a combined catalysis and adsorption approach. We found that fast pyrolysis oil can be upgraded through alcoholysis using n-butanol and tetrahydrofurfuryl alcohol, which are biomass-derived bulk chemicals. The reaction is acid catalyzed whereas water is continuously separated from the condensate mixture through molecular sieve adsorption. Under optimal conditions, the ultimate acidity and water content of the upgraded product are negligible.

Production of Jet Fuel-Range Hydrocarbons from Hydrodeoxygenation of Lignin over Super Lewis Acid Combined with Metal Catalysts.

Super Lewis acids containing the triflate anion [e.g., Hf(OTf)4 , Ln(OTf)3 , In(OTf)3 , Al(OTf)3 ] and noble metal catalysts (e.g., Ru/C, Ru/Al2 O3 ) formed efficient catalytic systems to generate saturated hydrocarbons from lignin in high yields. In such catalytic systems, the metal triflates mediated rapid ether bond cleavage through selective bonding to etheric oxygens while the noble metal catalyzed subsequent hydrodeoxygenation (HDO) reactions. Near theoretical yields of hydrocarbons were produced from lignin model compounds by the combined catalysis of Hf(OTf)4 and ruthenium-based catalysts. When a technical lignin derived from a pilot-scale biorefinery was used, more than 30 wt % of the hydrocarbons produced with this catalytic system were cyclohexane and alkylcyclohexanes in the jet fuel range. Super Lewis acids are postulated to strongly interact with lignin substrates by protonating hydroxyl groups and ether linkages, forming intermediate species that enhance hydrogenation catalysis by supported noble metal catalysts. Meanwhile, the hydrogenation of aromatic rings by the noble metal catalysts can promote deoxygenation reactions catalyzed by super Lewis acids.

Selective construction of polycyclic spirooxindoles via a Cu(OTf)2/HOTf-catalyzed domino reaction of o-arylalkynylacetophenones and 3-phenacylideneoxindoles.

Under the combined catalysis of Cu(OTf)2/HOTf, the domino annulation reaction of o-arylalkynyl acetophenones with 3-phenacylideneoxindoles in refluxing acetonitrile selectively afforded functionalized spiro[indoline-3,7'-tetrapheno[7,6-bc]furans] and spiro[indeno[1,2-b]naphtho[2,1-d]furan-7,3'-indolines] depending on the electronic effect of the substituents on both substrates.

ChemInform Abstract: Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes, Aryldiazonium Salts, and Aldehydes.

A highly selective multicomponent carbonyl allylation reaction of 1,3-butadienes, aryldiazonium tetrafluoroborates, and aldehydes has been established under the combined catalysis of palladium acetate and chiral anion phase transfer to render the favorable assembly of chiral Z-configured homoallylic alcohols in high yields and with excellent levels of enantioselectivity.

Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes, Aryldiazonium Salts, and Aldehydes.

A highly selective multicomponent carbonyl allylation reaction of 1,3-butadienes, aryldiazonium tetrafluoroborates, and aldehydes has been established under the combined catalysis of palladium acetate and chiral anion phase transfer to render the favorable assembly of chiral Z-configured homoallylic alcohols in high yields and with excellent levels of enantioselectivity.