Co-Harvest Phase-Change Enthalpy and Isomerization Energy for High-Energy Heat Output by Controlling Crystallization of Alkyl-Grafted Azobenzene Molecules

Photoisomerization-induced phase change are important for co-harvesting the latent heat and isomerization energy of azobenzene molecules.Chemically optimizing heat output and energy delivery at alternating temperatures are challenging because of the differences in crystallizability and isomerization.This article reports two series of asymmetrically alkyl-grafted azobenzene(Azo-g),with and without a methyl group,that have an optically triggered phase change.Three exothermic modes were designed to utilize crystallization enthalpy(△H_(c))and photothermal(isomerization)energy(△H_(p))at different temperatures determined by the crystallization.Azo-g has high heat output(275-303 J g^(-1))by synchronously releasing△H_(c)and△H_(p)over a wide temperature range(-79℃to 25℃).We fabricated a new distributed energy utilization and delivery system to realize a temperature increase of 6.6℃at a temperature of-8℃.The findings offer insight into selective utilization of latent heat and isomerization energy by molecular optimization of crystallization and isomerization processes.

Li-promoted C_(3)N_(4) catalyst for efficient isomerization of glucose into fructose at 50℃ in water

Efficient and selective glucose-to-fructose isomerization is a crucial step for production of oxygenated chemicals derived from sugars,which is usually catalyzed by base or Lewis acid heterogeneous catalyst.However,high yield and selectivity of fructose cannot be simultaneously obtained under mild conditions which hamper the scale of application compared with enzymatic catalysis.Herein,a Li-promoted C_(3)N_(4) catalyst was exploited which afforded an excellent fructose yield(40.3 wt%)and selectivity(99.5%)from glucose in water at 50℃,attributed to the formation of stable Li–N bond to strengthen the basic sites of catalysts.Furthermore,the so-formed N_(6)–Li–H_(2)O active site on Li–C_(3)N_(4) catalyst in aqueous phase changes the local electronic structure and strengthens the deprotonation process during glucose isomerization into fructose.The superior catalytic performance which is comparable to biological pathway suggests promising applications of lithium containing heterogeneous catalyst in biomass refinery.

Critical approaches in the catalytic transformation of sugar isomerization and epimerization after Fischer-History,challenges,and prospects

The transformation of aldose to ketose or common sugars into rare saccharides,including rare ketoses and aldoses,is of great value and interest to the food industry and for saccharidic biomass utilization,medicine,and the synthesis of drugs.Nowadays,high-fructose corn syrup(HFCS)is industrially produced in more than 10 million tons annually using immobilized glucose isomerase.Some low-calorie saccharides such as tagatose and psicose,which are becoming popular sweeteners,have also been produced on a pilot scale in order to replace sucrose and HFCS.However,current catalysts and catalytic processes are still difficult to utilize in biomass conversion and also have strong substrate dependence in producing high-value,rare sugars.Considering the specific reaction properties of saccharides and catalysts,since the pioneering discovery by Fischer,various catalysts and catalytic systems have been discovered or developed in attempts to extend the reaction pathways,improve the reaction efficiency,and to potentially produce commercial products.In this review,we trace the history of sugar isomerization/epimerization reactions and summarize the important breakthroughs for each reaction as well as the difficulties that remain unresolved to date.

Developing a highly scalable synthetic strategy for 5-amino-4-nitrobenzo[1,2-c:3,4-c']bis([1,2,5]oxadiazole)1,b-dioxide(CL-18)and investigating the influence of crystal engineering and positional isomerization on its safety and laser ignition performance

5-amino-4-nitrobenzo[1,2-c:3,4-c']bis([1,2,5]oxadiazole)1,6-dioxide(CL-18)exhibits significant potential as an initiating explosive.However,its current synthesis process remains non-scalable due to low yields and safety risks.In this study,we have developed a simple and safe synthetic route for CL-18.It was synthesized from 3,5-dihaloanisole in a four-step reaction with an overall yield exceeding 60%,surpassing all reported yields in the literature.Subsequently,recrystallization of CL-18 was successfully achieved by carefully selecting appropriate solvents and antisolvents to reduce its mechanical sensitivity.Ultimately,when DMF-ethanol was employed as the recrystallization solvent system,satisfactory product yield(>90%)and reduced mechanical sensitivity(IS=15 J;FS=216 N)were obtained.Additionally,CL-18 is derived from the rearrangement of oxygen atoms on i-CL-18 furoxan,and a comparative analysis of their physicochemical properties was conducted.The thermal stability of both compounds is similar,with onset decomposition temperatures recorded at 186 and 182℃respectively.Similarly,they exhibit 5 s breaking point temperatures of 236 and 237℃.Additionally,we present novel insights into the positional-isomerization-laser-ignition performance of CL-18 and its isomer i-CL-18 using laser irradiation for the first time.Remarkably,our findings demonstrate that i-CL-18 exhibits enhanced laser sensitivity,as it can be directly ignited by a 1064 nm wavelength laser,whereas CL-18 lacks this characteristic.

Synthesis of Pt/PMA-MIL-101 Catalyst and Its Performance in n-Heptane Isomerization

Hydroisomerization of n-heptane is an efficient method for producing gasoline with a high octane number.The focus of this study was to find a highly efficient catalyst that could both promote the conversion of n-heptane and inhibit the cracking side reaction.MIL-101(Cr)is a chromium-based metal-organic framework(MOF)with good hydrothermal stability,and exhibits a three-dimensional pore structure that is similar to that of zeolites.Using phosphomolybdic acid(PMA;H3PMo12O40·xH2O)can increase the number of Brønsted acid sites on MIL-101(Cr),which contributes to improving the catalytic performance during isomerization.In this study,0.4%Pt/PMA-MIL-101(Cr)catalyst was successfully crystallized at 220℃using a hydrothermal synthetic method.The results showed that the synthesized samples were mesoporousmicroporous composite materials with the typical octahedral structure,and the MIL-101(Cr)framework was not damaged following modification with PMA.It was found that 0.4%Pt30%PMA-MIL-101(Cr)exhibited the best performance for isomerization of n-heptane,with a conversion rate and selectivity at 260°C of 47.6%and 96.6%,respectively.After five hours of reaction,the conversion rate and selectivity of the catalyst remained above 38%and 80%,respectively.

Highly efficient isomerization of glucose to fructose over Sn-doped silica nanotube

Isomerization of glucose to fructose is a fundamental and key intermediate process commonly included in the production of valuable chemicals from carbohydrates in biorefinery.Enhancement of fructose yield is a challenge.In this work,Sn-doped silica nanotube(Sn-SNT)was developed as a highly efficient Lewis acid catalyst for the selective isomerization of glucose to fructose.Over Sn-SNT,69.1%fructose yield with 78.5%selectivity was obtained after reaction at 110◦C for 6 h.The sole presence of a large amount of Lewis acid sites in Sn-SNT without Brønsted acid site is one of the reasons for the high fructose yield and selectivity.Otherwise,high density of SiOH groups in Sn-SNT can ensure the presence of SiOH groups near the Sn sites,which is important for the isomerization of glucose to fructose,leading to the high fructose yield and selectivity.Furthermore,the Sn-SNT is recyclable.

Proton Transfer Isomerization of Pyrazole in the Ground State:σ vs π Mechanism and Water Assisting Effect

The proton transfer isomerization of pyrazole and the water assisting effect by looping 1 to 4 water molecules on the singlet state potential energy surface have been investigated by using hybrid density functional theory method （B3PW91） with a 6-311＋＋G^＊＊ basis set. Two mechanisms were proposed to explain the mono- and multi-water assisting effects, respectively. The reactants and products of all groups have been characterized on their potential energy surfaces. For the isomerizafion of monomolecule pyrazole, the isomeriz＇ation energy barrier is 46.4 kcal·mol^-1. For the monohydration assisting mechanism, the reactant complex is connected to the product complex via two saddle points. The corresponding isomerization barriers are 46.7and 23.0 kcal·mol^-1, respectively. As to the multihydration assisting mechanism, the isomerization barriers are 12.0, 10.9 and 13.14 kcal·mol^-1 accordingly, when the number of water molecules is 2, 3 and 4, respectively. The multihydration assisting isomerization can occur in water-dominated environments, for example, in the organism, and thereby is crucial to energy transference. The deproton and dehydrogen energies of monomolecule pyrazole and various hydrated pyrazoles were calculated and then found much bigger than the isomerization barriers of their relative complexes, suggesting the impossibility of deprotonation or dehydrogenation. The isomerization of pyrazole is a proton-coupling-electron-migration process, but two different mechanisms are noticed, viz. σ- and π-type mechanisms. The π-bond of pyrazole participates in isomerization in the π-type mechanism, whereas only o-electron takes part in isomerization in the σ-type mechanism.

Selective 3-OH Isomerization of Resibufogenin by Cell Suspension Cultures of Ginkgo biloba

Aim To modify the structure of resibufogenin by using Ginkgo bilobasuspension. Methods Young leaves of Ginkgo biloba were differentiated into callus in MS medium withonly 2,4-D as plant growth regulator. The callus was then transferred aseptically to liquid MSmedium exoge-nously supplemented with appropriate concentration of 6-BA, NAA and 2,4-D to establishsuspension cell culture system. Resibufogenin was administered into the well-grown cell cultures andincubated for 4 d. The products dissolved in the liquid phase of the cultures were extracted andpurified by silica gel column chromatography gradiently eluted with petroleum ether and acetonesystem. Results One transformed product was obtained in 40% yield after 4 d incubation, which wasidentified as 3-epi-resibufogenin on the basis of FAB MS, ~1H NMR and ^(13)C NMR spectroscopicanalysis and corresponding data reported in literature. Conclusion G. biloba suspension cultures canbe used as an enzyme system to biotransform resibufogenin, an animal-originated bufadienolide, into3-epi-resibufogenin.

Novel endo-to exo-isomerization of dicyclopentadiene

Endo-dicyclopentadiene was isomerized to exo-isomer by thermal treatment at evaluated temperature and pressure. The reaction temperature and pressure are key factors for this novel isomerization. This result may have great potential for practical application.

Isomerization of linear C5–C7 over Pt loaded on protonated fibrous silica@Y zeolite（Pt/HSi@Y）

A novel fibrous silica Y zeolite (HSi@Y) loaded with Pt has been studied based on its ability to produce protonic acid sites originating from molecular hydrogen. The Pt/HSi@Y was prepared using seed assisted crystallization followed by protonation and Pt-loading. The product formed had a spherical morphology with bicontinuous lamellar with a diameter in the range of 500-700 nm. The catalytic activity of the Pt/HSi@Y has been assessed based on light linear alkane (C5-C7) isomerization in a micro-catalytic pulse reactor at 423-623 K. A pyridine IR study confirmed that the introduction of fibrous silica on Y zeolite increased the Lewis acid sites corresponding with the formation of extra-framework Al which led to the generation of more protonic acid sites. A hydrogen adsorbed IR study showed that the protonic acid sites which act as active sites in the isomerization were formed via dissociative-adsorption of molecular hydrogen releasing electrons to the nearby Lewis acid sites. Thus, it is suggested that the presence of Pt and HSi@Y with a high number of Lewis acid as well as weak Bronsted acid sites improved the activity and stability in C5, C6 and C7 isomerization via hydrogen spill-over mechanism.

Isomerization of n-pentane catalyzed by amide-AlCl3-based ionic liquid analogs with various additives

The isomerization of n-pentane to generate high-quality blending components for clean gasoline was catalyzed by several amide-AlCl3-based ionic liquid(IL) analogs with various amides as donor molecules. The catalytic performance of these IL analogs was evaluated in a magnetic agitated autoclave operated in batch mode.IL analog based n-methylacetamide(NMA)-AlCl3 with the amide/AlCl3 molar ratio of 0.65 showed excellent performance toward n-pentane isomerization because 0.65 NMA-1.0 AlCl3 had a low viscosity and bidentate coordination structure. The influences of reaction time, reaction temperature, and stirring speed on the catalytic performance were also investigated. Optimal reaction conditions comprised the reaction time of 1 h, the reaction temperature of 40 °C, and the stirring speed of 1500 r·min-1. Under optimal condition, the n-C5 conversion,research octane number(RON) increment, total liquids yield, and isoparaffin yield in isomerized oil were56.80%, 13.51, 89.90 wt%, and 44.32 wt%, respectively. A new mathematical model was constructed to predict the relationships among RON increment, RON increment/n-C5 conversion ratio, and n-C5 conversion. The new model indicated that an appropriate conversion per pass of n-C5 did not exceed 50%–55%. Various cycloparaffin additives were used to improve the catalytic performance of 0.65 NMA-1.0 AlCl3. The n-C5 conversion increased from 56.80% to 67.32%. The RON increment, total liquids yield, and isoparaffin yield reached 17.83, 97.36 wt%,and 63.74 wt%, respectively.

Study on the pinene isomerization catalyzed by TiM

The isomerization reaction of pinene is one of the most important chemical reactions in the deep processing of pinene. The purpose of this study is to improve the performance of the metatitanic acid by composite. The composite metatitanic acid catalyst TiM was prepared by adding Mn elements in the preparation process. The catalytic performance of TiM was evaluated. Comparison of TiM and metatitanic acid catalyst(Ti-FGP), the reaction rate of TiM catalyst was faster, and after the reaction, the yield of camphene and tricyclene increased about 1%. The catalysts were characterized by an SEM, FT-IR and laser particle size analyzer. The results show that the pinene isomerization reaction requires the synergistic action of the Br?nsted acid and Lewis acid.Br?nsted acid has great influence on the activity of catalyst, and Lewis acid has a great influence on the selectivity of the catalyst. The structure and morphology of the catalyst have a certain effect on the selectivity of pinene isomerization reaction.

Experimental and kinetic study of n-heptane isomerization on nanoporous Pt-(Re,Sn)/HZSM5-HMS catalysts

Pt-（Sn,Re）/HZSM5-HMS catalysts were evaluated for n-heptane isomerization at 200–350 ℃.To characterize the catalyst,X-ray diffraction,X-ray fluorescene,Fourier transform infrared spectroscopy,ultraviolet-visible diffuse reflectance spectroscopy,temperature-programmed reduction of H2,temperature-programmed desorption of NH3,infrared spectroscopy of adsorbed pyridine,H2 chemisorption,nitrogen adsorption-desorption,scanning electron microscopy and thermogravimetric analysis were performed.Kinetics of n-C7 isomerization were investigated under various hydrogen and n-C7 pressures,and the effects of reaction conditions on catalytic performance were studied.The results showed that bi-and trimetallic catalysts exhibit better performance than monometallic catalysts for this reaction.For example,a maximum i-C7 selectivity（ 〉74%） and multibranched isomer selectivity（40%） were observed for Pt-Sn/HZSM5-HMS at 200 ℃.

A Promising MoO_x-based Catalyst for n-Heptane Isomerization

The SiO2 and g-Al2O3 supported MoOx catalyst and a MoOx-SiO2 catalyst have been studied in a conventional fixed-bed flow reactor for n-alkanes isomerization. It is shown that the MoOx-SiO2 catalyst with SiO2 framework, in which the bulk MoOx phase is large enough to form typical mesoporous structure, is promising in terms of its advantages of both improved mechanical strength and high catalytic properties over the supported MoOx and bulk MoOx catalyst.

Theoretical Study of Halogen Effect in Isomerization of 2-Halo-[9]-annulen Anion at the DFT Level

Cis-trans isomerization of [9]-annulenanion（1） and its 2-fluoro-,2-chloro-and 2-bromo-derivatives（2,3 and 4,respectively） were investigated at the HF/6-31G＊ and B3LYP/6-311＋＋G＊＊ levels of theory.Cis,cis,cis,cis structures appear more stable than their corresponding cis,cis,cis,trans-isomers.The relative height of energy barriers for cis-trans isomerization is：2cis 〉1cis 〉3cis〉 4cis.This trend for the reverse trans-cis isomerization follows the electronegativity of the substituent at C-2（2trans 3trans 4trans 1trans）.

Modeling of Isomerization of C_8 Aromatics by Online Least Squares Support Vector Machine

The least squares support vector regression (LS-SVR) is usually used for the modeling of single output system, but it is not well suitable for the actual multi-input-multi-output system. The paper aims at the modeling of multi-output systems by LS-SVR. The multi-output LS-SVR is derived in detail. To avoid the inversion of large matrix, the recursive algorithm of the parameters is given, which makes the online algorithm of LS-SVR practical. Since the computing time increases with the number of training samples, the sparseness is studied based on the pro-jection of online LS-SVR. The residual of projection less than a threshold is omitted, so that a lot of samples are kept out of the training set and the sparseness is obtained. The standard LS-SVR, nonsparse online LS-SVR and sparse online LS-SVR with different threshold are used for modeling the isomerization of C8 aromatics. The root-mean-square-error (RMSE), number of support vectors and running time of three algorithms are compared and the result indicates that the performance of sparse online LS-SVR is more favorable.

Chloroaluminate ionic liquid catalyzed isomerization of n-pentane in the presence of product distribution improver

The ionic liquid Et3NHC1-2AIC13 can catalyze the isomerization of n-pentane. This paper investigates the ionic liquid catalyzed isomerization performance of n-pentane with several product distribution improvers in an autoclave. The product distribution of n-pentane isomerization could be improved by such improvers as benzene, cyelohexane, and methyl cyclohexane at the expense of conversion of n-pentane. The optimal product distribution improver was determined to be cyclohexane. The yield of isomerate and the selectivity of liquid isoalkanes increased, whereas the conversion of n-pentane decreased, with increasing cyclohexane amount. At the same conversion of n-pentane, the research octane number （RON） of liquid product, with cyclohexane amount of 0.5 wt%, was about 1.3 higher than that without cyclohexane. At the same reaction conditions, the presence of cyclohexane enhanced the yield of isomerate, the selectivity of liquid isoalkanes, and the RON of the liquid product, but reduced the conversion of n-pentane.

Triphenylphosphine-catalyzed isomerization of alkynyl ketones in aqueous solution

An efficient isomerization of alkynyl ketones to (E,E)-diene ketones was developed. The reaction catalyzed by 20 mol% triphenylphosphine in aqueous media gave the desired products in good yields.

Effect of Ni Loading on the Catalytic Properties of Molybdenum Oxides for the Isomerization of Heptane

The catalytic properties of MoOx and incorporation Ni onto the MoOx for the isomerization of heptane have been investigated under atmospheric pressure at different conditions such as different flow rate of H2, different reaction temperature etc.. Compared with MoOx, the Ni addition to the MoOx markedly improved the isomerization activity of heptane by improving the reducibility of MoO3 and activation of H2 in reaction.

Isomerization of n-octane on NiW/HSAPO-11 Catalyst

The catalyst NiW/HSAPO-11 was prepared by impregnating Ni and W onto HSAPO-11 zeolite with two different methods. The isomerization and aromatization properties were investigated with an microreactor using n-octane as a feedstock. NiW/HSAPO-11 shows a high hydroconversion activity of n-octane, and the optimum operating parameters for the catalyst to produce high octane number products were: 400℃, 2.0MPa, VH2:Vn-octane= 400:1, liquid hourly space velocity LHSV=1.0h-1. Under the optimum reaction condition, the conversion efficiency, C5 liquid + product selectivity, isomerization and aromatization product selectivity were 69.80%, 56.95%, 79.73% and 1.29% respectively. The catalyst (S1) impregnated with Ni and W after the HSAPO-11 zeolite was combined with Al2O3 matrix, performed better than the catalyst (S2) impregnated with Ni and W before combining with the Al2O3 matrix.