Thermal stable Pt clusters anchored by K/TiO_(2)—Al_(2)O_(3)for efficient cycloalkane dehydrogenation

Catalytic dehydrogenation of cycloalkanes is considered a valuable endothermic process for alleviating the thermal barrier issue of hypersonic vehicles.However,conventional Pt-based catalysts often face the severe problem of metal sintering under high-temperature conditions.Herein,we develop an efficient K_(2)CO_(3)-modified Pt/TiO_(2)—Al_(2)O_(3)(K—Pt/TA)for cycloalkane dehydrogenation.The optimized K—Pt/TA showed a high specific activity above 27.9 mol·mol^(-1)·s^(-1)(H_(2)/Pt),with toluene selectivity above 90.0%at 600℃with a high weight hourly space velocity of 266.4 h^(-1).The introduction of alkali metal ions could generate titanate layers after high-temperature hydrogen reduction treatment,which promotes the generation of oxygen vacancy defects to anchored Pt clusters.In addition,the titanate layers could weaken the surface acidity of catalysts and inhibit side reactions,including pyrolysis,polymerization,and isomerization reactions.Thus,this work provides a modification method to develop efficient and stable dehydrogenation catalysts under high-temperature conditions.

Computer-aided ionic liquid design for alkane/cycloalkane extractive distillation process

A computer-aided ionic liquid design(CAILD) study is presented for the frequently encountered alkane/cycloalkane separations in petrochemical industry. Exhaustive experimental data are first collected to extend the UNIFAC-IL model for this system, where the proximity effect in alkanes and cycloalkanes is considered specifically by defining distinct groups. The thermodynamic performances of a large number of ILs for 4 different alkane/cycloalkane systems are then compared to select a representative example of such separations. By applying n-heptane/methylcyclohexane extractive distillation as a case study, the CAILD task is cast as a mixed-integer nonlinear programming(MINLP) problem based on the obtained task-specific UNIFAC-IL model and two semi-empirical models for IL physical properties. The top 5 IL candidates determined by solving the MINLP problem are subsequently introduced into Aspen Plus for process simulation and economic analysis, which finally identify 1-hexadecyl-methylpiperidinium tricyanomethane([C_(16)MPip][C(CN)_3]) as the best entrainer for this separation.

A density functional theory study on the decomposition of aliphatic hydrocarbons and cycloalkanes during coal pyrolysis in hydrogen plasma

To get deep understanding of the reaction mechanism of coal pyrolysis in hydrogen plasma, the decomposition reaction pathways of aliphatic hydrocarbons and cycloalkanes, which are two main components in volatiles from coal, were investigated. Methane and cyclohexane were chosen as the model compounds. Density functional theory was employed, and many reaction pathways were involved. Calculations were carried out in Gaussian 09 at the B3LYP/6-31G（d,p） level of the theory. The results indicate that the main pyrolysis products of methane and cyclohexane in hydrogen plasma are both hydrogen and acetylene, and the participation of active hydrogen atoms makes dehydrogenation reactions more favorable. H2 mainly comes from dehydrogenation process, while many reaction pathways are responsible for acetylene formation. During coal pyrolysis in hydrogen plasma, three main components in volatiles like aliphatic hydrocarbons, cycloalkanes and aromatic hydrocarbons lead to the formation of hydrogen and acetylene, but their contributions to products distribution are different.

Catalyst-free and solvent-free oxidation of cycloalkanes(C5-C8) with molecular oxygen:Determination of autoxidation temperature and product distribution

Autoxidation of cycloalkanes （C5-C8） with molecular oxygen under catalyst-free and solvent-free conditions was conducted systematically for the first time, focusing on the autoxidation temperature and product distribution. The autoxidation of cyclopentane, cyclohexane, cycloheptane and cyclooctane occurs at 120 ℃, 130 ℃, 120 ℃, and 105 ℃ respectively, with obvious oxidized products formation. At 140 ℃, 145 ℃, 130 ℃ and 125 ℃, acceptable yields of the oxidized products could be obtained for them, and the oxidized product distributions were investigated in detail. The autoxidation of cycloalkanes follows the pseudo-first-order kinetic model and the apparent activation energies （Ea） for the autoxidation of cyclopentane and cyclohexane are 159.76 kJ. tool-1 and 86.75 kJ. mol-1 respectively. This study can act as an important reference in screen of suitable reaction temperature and comparison of the performance of various catalysts in the catalytic oxidation of cycloalkanes in the attempt to enhance the oxidized product selectivity.

Enumeration of Stereoisomers of Chiral and Achiral Derivatives of Monocyclic Cycloalkanes Having Heteromorphous Alkyl Substituents with Distinct Length <i>k</i>

A combinatorial method based on the determination of the averaged weight of permutations controlling the chirality/achirality fittingness of 2n substitution sites of the monocyclic cycloalkane allows to obtain generalized functional equations for direct enumeration of enantiomers pairs and achiral skeletons of any derivatives of monocyclic cycloalkanes having heteromorphic alkyl substituents with the distinct length k with the empirical formula , wherein at least two alkyl groups??of the distinct size ?each. ?is the number of alkyl radicals ?of the system??verifying the relation . The integer sequences of enantiomer pairs and achiral skeletons are given for substituted derivatives of monocyclic cycloalkane for n = 3, 4 and k = 3, 4, 5. The composite stereoisomerism of this particular compound is also highlighted.

Dissolution of Expanded Polystyrene in Cycloalkane Solutions

Feasibility of dissolution and utilization of expanded polystyrene in cycloalkane solutions was investigated in this work. The dissolution process of expanded polystyrene in several cycloalkane solutions decalin, cyclohexane and methyl cyclohexane was studied. The effect of dissolution temperature, mechanical agitation, ultrasonic wave and stirring rate was studied under optimized conditions. Mass transfer coefficients were fitted. The results showed that the dissolution rate of expanded polystyrene in different cycloalkane solutions was ranked as decalin > methyl cyclohexane > cyclohexane;higher dissolution temperature and faster stirring rate could speed up the dissolution of expanded polystyrene;the effect of mechanical agitation was superior to ultrasonic condition;the solubility of top face was better than side face and under face.

Photoinduced decatungstate-catalyzed direct coupling of cycloalkanes and cyclic aldimines

We first describe a photoinduced decatungstate-catalyzed direct coupling of cycloalkanes and cyclic aldimines.The desired products were generated in moderate to good yields with wide substrate scope under mild reaction conditions.The mechanistic study revealed a radical process.In addition,the usefulness of the reaction in organic synthesis was proved by the scale-up synthesis as well as the late-stage modification of drug-like molecules.

Sustainable production of high-energy-density jet fuel via cycloaddition reactions

Developing an energy supply-chain based on renewable biomass holds great potential to build a low carbon society.High-energy-density(HED)jet fuel,featuring unique fused/strained cycloalkanes,is of great significance for volume-limited military aircrafts,as their high density and combustion heat can extend flight duration and increase the payload.Therefore,the exploration of biomass-based routes towards HED fuel has drawn much attention over the past decade.Cycloaddition reaction features rapid construction of various carbocycles in an atom-and step-economical fashion.This elegant strategy has been widely applied in the manufacture of sustainable HED fuel.Here we carefully summarize the progress achieved in this fascinating area and the review is categorized by the cycloaddition patterns including[4+2],[2+2],[4+4],and[2+1]cycloadditions.Besides,the energy densities of the as-prepared biofuels and petroleumbased fuels(conventional Jet-A and advanced JP-10)are also compared.This review will provide important insights into rational design of new HED fuel with different ring-types/sizes and inspire the chemists to turn those literature studies into practical applications in military field.

Research Advances on Cyclohexane Catalytic Cracking

This article elaborates on the research achievements of domestic and foreign researchers in exploring the conversion pathways and reaction mechanisms of cyclohexane catalytic cracking in recent years.It analyzes the effects of different catalysts and process conditions on the conversion laws of cyclohexane,summarizes the conversion pathways of cyclohexane,and discusses the chemical mechanisms of several main reactions of cyclohexane in catalytic cracking,such as cracking,isomerization,hydrogen transfer,dehydrogenation,and alkylation;Several advanced characterization methods and common research methods were listed,and prospects for future development in this field were proposed based on existing research.

Geochemical characteristics and origin of light hydrocarbons in biogenic gas

The light hydrocarbon geochemical characteristics of biogenic gases from Sebei 1 gas field in the Qaidam Basin, Baoshan gas field in the Baoshan Basin and Alaxin gas field, Puqian gas pool, Aonan gas pool in the Songliao Basin are studied and the origin is discussed based on the composition and isotope data of gases. The isoalkane contents among light hydrocarbons in natural gas show a negative relationship with δ13C1 values. The isoalkane contents of the gases with δ13C1 values of less than ?60‰ are also high with more than 40% among light hydrocarbons in Sebei 1 gas field and Puqian gas pool. Moreover, the 2,2-dimethylbutane and 2-methylpentane, mainly sourced from bacteria, have predominance among isoalkanes, which suggests that light hydrocarbons in biogenic gases from these gas fields or pools were probably generated by microbial action. However, the cycloalkane contents among light hydrocarbons in biogenic gas are related to δ13C1 values positively. In Alaxin gas field and Aonan gas pool, where δ13C1 values of biogenic gases are less than ?60‰, the average contents of cycloalkane are higher than 44%. Light hydrocarbons among biogenic gases from these gas fields were probably generated by catalysis. The isoalkane and cycloalkane contents among light hydrocarbons from biogenic gases in the Baoshan gas field are both high, which might be generated by these two actions. The results show that the data of light hydrocarbons in biogenic gas can provide important information for understanding the generation mechanisms of light hydrocarbons during geological evolution and identifying biogenic gas and low mature gas.

All-at-once arrangement of both oxygen atoms of dioxygen into aliphatic C(sp^(3))–C(sp^(3))bonds for hydroxyketone difunctionalization

Bothβ-andγ-hydroxyketone structures are important units in biologically active molecules,synthetic drugs and fine chemicals.Although there are some routes available for their manufacture from pre-functionalized groups on one or two matrix molecule(s),the approaches to simply and simultaneously deposit two oxygen atoms from dioxygen into two specific C(sp^(3))positions of pure saturated hydrocarbons have rarely succeeded because they are involved in the targeted activation of three inert C–Hσbonds all at once.Here,we show that a TiO_(2)-CH_(3)CN photocatalytic suspension system enables the insertion of dioxygen into one C(sp^(3))–C(sp^(3))bond of strained cycloparaffin derivatives,by which difunctionalized hydroxyketone products are obtained in a one-pot reaction.With the cleavage event to release strain as the directional driving force,as-designed photocatalytic reaction systems show 21 examples ofβ-hydroxyketone products with 31%–76%isolated yields for three-membered ring derivatives and 5 examples ofγ-hydroxyketone products with 30%–63%isolated yields for four-membered ring substrates.^(18)O isotopic labeling experiments using^(18)O2,Ti^(18)O_(2) and intentionally added H218O,respectively,indicated that both oxygen atoms of hydroxyketone products were exclusively from dioxygen,suggesting a previously unknown H^(+)/TiO_(2)-e−catalyzed arrangement pathway of the hydroperoxide intermediate to convert dioxygen into hydroxyketone units.