Catalysts For Isomerization Research Articles

Polyvinyl alcohol templated synthese of hierarchical SAPO-11

This work reports that the polyvinyl alcohol successfully templates the intracrystal mesoporous structure of hierarchical SAPO-11 molecular sieves. The structures of prepared hierarchical SAPO-11 materials and a conventional SAPO-11 simultaneously synthesized are characterized by X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy and high resolution transmission electron microscopy. The characterizations demonstrate that this synthesized hierarchical SAPO-11 possesses a mesopore structure with a much regular pore size distribution. Importantly, these mesopores are intracrystal but not intercrystal. The bifuntional isomerization catalyst with this hierarchical SAPO-11 as support shows a high selectivity in hydroisomerization reaction of hexane, evidencing that the catalytic selectivity is improved by introduction of mesopore structure into the SAPO-11 crystal. The templating mechanism of polyvinyl alcohol in formation of mesopores is well discussed at the ending. This work provides a potential template to prepare hierarchical catalyst materials.

Micro-mesoporous MCM-41/ZSM-5 supported Pt and Pd catalysts for hydroisomerization of C-8 aromatic fraction

The hierarchical MCM-41/ZSM-5 aluminosilicate synthesized via a double-template procedure using CTAB and TPAOH was applied as a support for Pt and Pd isomerization catalysts with metal loading of 0.5 wt.%. The formation of micro-ZSM-5, as well as meso-MCM-41 phases, was confirmed by XRD, TEM, SEM, and FT-IR. The element composition, textural properties and acidity both of MCM-41/ZSM-5 composite and noble metals supported catalysts were structurally characterized by TGA, N2 sorption, XRF, and NH3-TPD. Examining the catalytic evaluation of MCM-41/ZSM-5 supported Pt and Pd catalysts in hydroisomerization of C8 aromatic fraction in a fixed bed flow-type unit at 280−420 °C, LHSV of 1–6 h−1 and H2:feed of 1200–3600, showed that the Pt catalyst is more active compared to its industrial counterpart and provides high m-xylene and ethylbenzene conversions predominantly with p-xylene formation at 340 °C with LHSV of 1.0 h−1 (H2/feed = 2400) as well as for LHSV of 3.5 h−1 (H2/feed = 1200).

Effect of Calcination Temperature on Structural Properties and Catalytic Performance of Novel Amorphous NiP/Hβ Catalyst for n-Hexane Isomerization

To study how calcination temperature influences the structural properties and catalytic performance of a novel amorphous NiP/Hβ catalyst, amorphous NiP/Hβ catalysts calcined at different temperatures were prepared for n-hexane isomerization. The optimum calcination temperature was determined, and the effect of calcination temperature on the structural properties of the catalysts was investigated using different characterization methods, such as XRD, TPD and so on. It was found that the optimum calcination temperature was 200 °C. Simultaneously, the amorphous NiP/Hβ catalyst showed good application potential as a non-noble metal catalyst. Calcination temperatures from 100 to 400 °C had almost no effect on pore properties. Meanwhile, the acid properties of the amorphous NiP/Hβ catalyst were affected very little by calcination temperature. By increasing calcination temperature, the dispersion state of amorphous NiP became worse at 300 °C, and then the structure of NiP changed from an amorphous structure into a crystalline structure at 400 °C. In addition, the catalyst became more difficult to reduce with the increase in calcination temperature. Combined with the results of n-hexane isomerization catalyzed by different samples, the mechanism by which calcination temperature affects n-hexane isomerization over catalyst was revealed. It was shown that for the amorphous NiP/Hβ catalyst, calcination temperature influences the catalytic performance mainly by affecting the dispersion degree and structure of active components.

Monosaccharides Dehydration Assisted by Formation of Borate Esters of α-Hydroxyacids in Choline Chloride-Based Low Melting Mixtures.

The synthesis of 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) by hexoses and pentoses dehydration is considered as a promising path to produce materials from renewable resources. Low-transition-temperature mixtures (LTTMs) enable selective (>80%) dehydration of ketoses to furanic derivatives at moderate temperature (<100°C). However, aldoses dehydration generally requires higher temperatures and an isomerization catalyst. Chromium trichloride has been reported as one of the most efficient catalyst but its kinetic inertness could limit its performances below 100°C. Consequently, we investigate herein boric acid catalysis of aldoses dehydration in LTTMs based on choline halides and organic acids at 90°C. The limited activity of boric acid regarding furanic compounds synthesis (e.g., 5% 5-HMF yield and 23% glucose conversion after 1 h at 90°C with maleic acid) can be enhanced through tetrahydroxyborate esters (THBE) formation with α-hydroxyacids (e.g., 19% 5-HMF yield and 61% glucose conversion after 1 h at 90°C). THBE formation is however associated with H3O+ generation favoring the appearance of side products (humins). We demonstrate that boric acid catalysis is not straightforward and that the use of THBE under moderate acidity should be further investigated to limit humins formation and promote furanic derivatives synthesis.

Aluminum oxide carrier for a catalyst for low-temperature isomerization of hydrocarbons

Objectives. Determine the necessary conditions for obtaining a granulated η-Al2O3 carrier, investigate its structural and strength properties, and evaluate its activity for the model n-butane isomerization reaction.Methods. Samples containing bayerite structure aluminum trihydroxide were synthesized by precipitation from aqueous solutions of aluminum nitrate with ammonia under isothermal conditions at a constant pH value. The samples of the granulated carrier were obtained using an extrusion method when the composition of molding pastes was varied by tuning the ratio of bayerite- and η-Al2O3 -containing components and introducing polyvinyl alcohol.Results. The influence of the preparation conditions on the structural and strength properties of the active Al2O3 granules is evaluated. Samples of the aluminum oxide carrier were tested for a model reaction of low-temperature isomerization of n-butane, demonstrating a sufficiently high selectivity and reasonable prospects for use as catalysts for low-temperature isomerization of hydrocarbons.Conclusions. Increasing the content of the polyvinyl alcohol in the molding paste from 0.4 to 1.8 wt % is accompanied by an increase in the predominant sizes of the mesopores in the range of 10–50 nm and pores in the range of 50–80 nm, explaining the high values of all recorded parameters for the process of isomerization of n-butane.

Pd/HZSM-5 catalyst for n-hexane isomerization: Properties, activities, and deactivation

The activity of n-hexane isomerization with 0,8 %kl Pd/HZSM-5 was studied in a micro reactor in the temperature range of 225-325 oC at 0,1 Mpa with the molar ratio H2/ hydrocarbon of 5.92, n-hexane concentration of 9.2 %mol, GHSV 2698 h-1 at atmospheric pressure. The catalyst owned suitable acidity, reasonable reductivity, good metal dispersion, and appropiate balance between metallic and acidic functions. The catalyst had high activity but low stability. The cause of deactivation was examined via a comparison of physico-chemical properties between a fresh catalyst and a used one. There was no metal sintering. The mono-metallic catalyst performed high activity for n-hexane hydro-isomerization but less stable. Deactivation is mainly attributed to coke formation. Catalyst activity and stability were significantly improved with activity of 0,7 MPa compared to that of 0,1 MPa at elevated pressure. The catalyst Pd-Co/HZSM-5 is capable of resisting against coke, thereby exhibiting high stability at 0,1 MPa. The highly stable and active catalyst helped to form high quality products to result in environment-friendly gasoline.

Computational studies on nonenzymatic succinimide-formation mechanisms of the aspartic acid residues catalyzed by two water molecules

In the biological proteins, aspartic acid (Asp) residues are prone to nonenzymatic isomerization via a succinimide (Suc) intermediate. Asp-residue isomerization causes the aggregation and the insolubilization of proteins, and is considered to be involved in various age-related diseases. Although Suc intermediate was considered to be formed by nucleophilic attack of the main-chain amide nitrogen of N-terminal side adjacent residue to the side-chain carboxyl carbon of Asp residue, previous studies have shown that the nucleophilic attack is more likely to proceed via iminol tautomer when the water molecules act as catalysts. However, the full pathway to Suc-intermediate formation has not been investigated, and the experimental analyses for the Asp-residue isomerization mechanism at atomic and molecular levels, such as the analysis of the transition state geometry, are difficult. In the present study, we computationally explored the full pathways for Suc-intermediate formation from Asp residues. The calculations were performed two types of reactant complexes, and all energy minima and TS geometries were optimized using B3LYP density functional methods. As a result, the SI-intermediate formation was divided into three processes, i.e., iminolization, cyclization, and dehydration processes, and the activation energies were calculated to be 26.1 or 28.4 kcal mol−1. These values reproduce the experimental data. The computational results show that abundant water molecules in living organisms are effective catalysts for the Asp-residue isomerization.

Tandem Catalysts for Polyethylene Upcycling: A Simple Kinetic Model.

Of all plastics, the most abundantly produced is polyethylene, most of which is destined for landfills, shipping ports, and natural environments. The limited degradability and recyclability of this synthetic polymer motivates the development of chemical recycling methods. One possible approach consists of selective depolymerization to propylene with tandem olefin metathesis and double bond isomerization catalysts. In this paper, we transform thousands of coupled rate equations, pseudo-steady-state approximations, and local density approximations into one simple and analytically solvable Fokker-Planck type equation. The Fokker-Planck equation gives concise expressions for the rate of propylene production and polymer molecular weight evolution as functions of catalyst concentrations, rate constants, and ethylene concentrations.

Effective Dispersion of MgO Nanostructure on Biochar Support as a Basic Catalyst for Glucose Isomerization

Glucose isomerization to fructose is one of the most important reactions in the field of biomass valorization. We demonstrate wood waste valorization with MgCl2 salt to synthesize an environment-fr...

Reagent-Triggered Isomerization of Fluxional Cluster Catalyst via Dynamic Coupling.

Metallic cluster catalysts have many thermodynamically accessible isomers with diverse active sites and low reaction barriers, and lately a strong hypothesis emerged that the many catalyst states collectively drive the catalysis. However, it remained a hypothesis that catalyst isomerization is actually kinetically feasible under the current reaction conditions. Using high-temperature dynamics simulations and sampling, a range of orientations, and vibrational energy distributions, we probe how thermal effects and molecular events affect cluster catalyst dynamics. We show that even such a delicate affair as the dissociation or scattering of a methane molecule on the heavy and thus slow Pt13 cluster triggers substantial isomerization of the catalyst, far beyond thermal at 700 K. A kinetic coupling between the methane activity and cluster catalyst dynamics is observed. In return, the thermal dynamics of the cluster affects the methane reaction and scattering probabilities. Hence, molecular events at the surfaces of fluxional cluster catalysts should facilitate the population of an ensemble of catalyst states under the current reaction conditions, with implications for available active sites, reaction mechanisms, and apparent rates.

Bimetallic Bifunctional Pt-NiP/Hβ as a Novel and Highly Efficient Catalyst for n-Hexane Isomerization

A novel bimetallic bifunctional Pt–NiP/Hβ isomerization catalyst was successfully prepared by introducing a small amount of noble metal Pt into the NiP on the Hβ carrier. The catalyst demonstrated superior catalytic activity to Pt/Hβ and NiP/Hβ catalysts for n-hexane isomerization, due to the good surface property, the synergistic effect of the two metals, the suitable match between acid site and metal site, as well as good reduction stability. The effects of Pt loading and NiP addition amount on the surface property were studied comprehensively through a series of characterization, and the correlation among surface property with catalytic behavior was also analyzed. The results indicated that the Pt (0.1 mol%)–NiP (10 mol%)/Hβ catalyst had good structural characters, surface acid property and an uniform distribution of NiP and Pt active components on surface, which is helpful to obtain a highly efficient catalytic performance. Additionally, the influence of reduction/reaction conditions on the catalytic activity, as well as the catalyst tolerance to water and thiophene sulfur, was investigated furtherly.

Acid Properties of Hierarchical Zeolites Y.

The article reviews different strategies towards obtaining mesoporous zeolites Y: desilication; surfactant templating and assembly of zeolite crystals. The impact of those methods on physicochemical properties is covered, with a special focus on the acidity of the samples measured with infrared (IR) spectroscopy. The methods of characterization of acidity are presented. Quaternary ammonium cations used for desilication lead to obtaining crystalline; mesoporous and highly acidic zeolites. Si-OH-Al groups of extremely high acidity can be produced by calcination in a humid atmosphere. When the conditions are optimized, post-synthetic surfactant templating allows crystalline mesoporous zeolite to be obtained with no loss of material. All mesoporous zeolites Y proved to be active catalysts in liquid phase isomerization, catalytic cracking, and other reactions.

Alkane isomerization over sulfated zirconia solid acid system

Sulfated zirconia (SZ) and its modified versions attract great interest in recent years, because of their promising potential in n-alkane isomerization. The oxidative and protonation routes are active and interactional in n-alkane activation over SZ catalysts. The bimolecular reaction becomes dominant with increasing the density of active sites on SZ surface and decreasing the carbon chain of feed. Pentane and hexane are mainly isomerized by protonated cyclopropane mechanism, while which is thermodynamically unflavored for n-butane isomerization. The deactivation of SZ catalysts is primarily caused by the loss of superacidity and oxidizing ability, resulted from the structure changes of sulfate species. Several strategies for improving the activity of SZ are reviewed. The intrinsic structure-reactivity relationship of SZ catalysts in alkane isomerization is updated to illuminate the prerequisite for the highly active catalysts and the mechanism of active sites formation. The applications of Pt/SZ in fixed-bed and unmodified SZ in circulating fluidizing bed in light alkanes isomerization are compared with the conventional technologies based on the chlorinated alumina catalysts. Finally, the future study of SZ catalysts is outlooked from the academic investigations to the industrial applications.

Isomerization Kinetics of Glucose to Fructose in Aqueous Solution with Magnesium‐Aluminum Hydrotalcites

AbstractMg−Al hydrotalcites for catalyzing glucose isomerization to fructose are prepared. Effects of atom ratios of Mg/Al ranging from 1 to 4 and calcination temperatures from 250–650 °C on catalytic performance were examined systematically. It was found that the hydrotalcite (Mg2Al1LDH) calcined at 450 °C with an atom ratio of Mg/Al=2 is an excellent catalyst for glucose isomerization. Characterizations by SEM, EDS, TEM, XRD, FTIR, TG and BET demonstrated that the formed oxide condensed phase as well as the interaction with the alumina helps promote glucose isomerization reaction due to their appropriate basic sites at high calcination temperature. With Mg2Al1‐450 as the catalyst, kinetic model analysis confirmed that the reaction of glucose isomerization to fructose was an exothermal reversible reaction; both the forward and reverse reactions are quasi‐first‐order reactions with activation energies of 71.82 kJ/mol and 48.15 kJ/mol, respectively, while the side reaction is a zero‐order reaction with an activation energy of 94.22 kJ/mol. Therefore, high isomerization reaction temperature is not beneficial to enhance the yield and selectivity of fructose.

Isomerization of 1-Butene to 2-Butene Catalyzed by Metal–Organic Frameworks

MIL-100 and MIL-101 were synthesized and evacuated to generate a series of heterogeneous catalysts for isomerization of 1-butene. Their crystal structures and pore properties were characterized by ...

MgO-ZrO2 Mixed Oxides as Effective and Reusable Base Catalysts for Glucose Isomerization into Fructose in Aqueous Media.

MgO-ZrO2 mixed oxides prepared with different Mg/Zr atomic ratios (denoted as xMZ: where x is the atomic ratio of Mg/Zr) are investigated for the glucose isomerization to fructose in water at 95 °C. The highest fructose yield of 33 % is obtained over 0.76MZ with ≈74 % selectivity after 3 h. To gain insight into the structure-activity relationships, the prepared catalysts are characterized by N2 physisorption, XRD, FTIR and CO2 -TPD. The results indicate that the addition of MgO drastically changed the textual property of ZrO2 and increased the number of basic sites. The kinetic studies revealed that the Lewis basic sites (cus-O2- ) generated from the highly dispersed MgO are the active sites responsible for the enhanced isomerization activity. Notably, MZ is reusable for four runs without a significant decrease in catalyst activity. Accordingly, this study provides an easily prepared, cheap, and recyclable catalyst that may hold great potential for fructose production.

N-Doped Carbon Materials as Heterogeneous Catalysts for High Efficiency Isomerization Glucose to Fructose in Aqueous Media

Fructose is not only an important food and beverage ingredient, but also a renewable resource for production of bio-chemicals. In this paper, a series of N doped mesoporous carbon materials (MCNs) were prepared and evaluated as heterogeneous catalysts for catalytic isomerization of glucose to fructose. The MCNs were prepared through carbonization of p-phenylenediamine disulfate and the effects of desulfonation with NaOH and hydrogenation treatments were examined. It is found that the molar ratio of H2SO4/pPDA crucially affects the porous structure and the nitrogen content. Desulfonation with NaOH treatment could largely eliminate the sulfonic groups on the carbon edges and thus enhance the basicity of the MCN materials, whereas hydrogenation reduction could modify the N atom species and reinforce the strength of the basic sites, as a result enhancing the catalytic activities in glucose isomerization to fructose. Among all of the prepared MCN samples, MCN-2-DH showed an excellent activity in aqueous solution, which afforded a fructose yield of 31.6% with 84.6% selectivity.

Remote Functionalization of α,β-Unsaturated Carbonyls by Multimetallic Sequential Catalysis.

The remote functionalization of α,β-unsaturated carbonyls by an array of multimetallic sequential catalytic systems is described. The reactions are triggered by hydrometalation using [Pd-H] or [Ru-H] isomerization catalysts and driven by the formation of thermodynamically more stable 1,2-vinyl arenes. The Pd-catalyzed deconjugative isomerization was combined with a Cu-catalyzed β-borylation of the transiently generated styrenyl derivatives to deliver a range of products that would not be accessible with the use of a single catalyst. [Pd/Cu] catalytic systems were also identified for the highly enantioselective α-hydroboration and α-hydroamination of the styrenyl intermediates. Difunctionalization simultaneously at the benzylic and homobenzylic positions was achieved by combining the isomerization process with Sharpless asymmetric dihydroxylation (SAD) using [Pd/Os] or [Ru/Os] couples. Starting from a simple α,β-unsaturated ester, an isomerization/dihydroxylation/lactonization sequence gave access to a naturally occurring γ-butyrolactone in good yield, with excellent diastereo- and enantioselectivity.

Tuneable functionalities in layered double hydroxide catalysts for thermochemical conversion of biomass-derived glucose to fructose

Layered double hydroxides (LDHs) with varying crystallite sizes (2.6–43 nm), layer numbers (3–70), specific surface area (18–455 m2 g−1), pore volume (0.025–1.6 mL g−1), and functional groups were synthesised via conventional urea hydrolysis and co-precipitation methods and aqueous miscible organic solvent (AMOST) treatment. They were evaluated as the solid base catalysts for the thermochemical isomerisation of biomass-derived glucose to fructose with the aim of establishing the structure-performance relationships for carbon-efficient biorefinery. The results showed that the fructose yield increased with increasing crystallite size of LDHs due to the enhanced exposure of active sites. However, excessive increase in the structural accessibility could be detrimental because high hydrophilicity potentially resulted in water clusters surrounding the active sites and hindering their interaction with glucose. Nano-sized particles in small quantity that were visually indiscernible may partially account for the catalytic activity. The kinetics test suggested that the conversion of glucose to intermediates may act as the rate-determining step when the reaction temperature increased. The activation energy for the LDH-catalysed glucose conversion was estimated to be 52.8 kJ mol−1. The highest fructose yield of 25 mol% was achieved at 120 °C for 5 min in water. The recycling test suggested that the catalytic performance became stable after the second run, possibly due to the formation of a passive layer. This study elucidates the structure-controlled functionalities of the LDH catalysts to serve a base-catalysed biorefinery reaction, and provides mechanistic insights into the active components and the catalyst transformation during thermochemical biomass conversion.

Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydrofunctionalization and Formal Retro-hydrofunctionalization.

We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si-F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.