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The stereoselective activation of alkanes constitutes a long-standing and grand challenge for chemistry. Although metal-containing enzymes oxidize alkanes with remarkable ease and selectivity, chemical approaches have largely been limited to transition metal–based catalytic carbon–hydrogen functionalizations. Alkanes can be protonated to form pentacoordinated carbonium ions and fragmented into smaller hydrocarbons in the presence of strong Brønsted acids. However, catalytic stereocontrol over such reactions has not previously been accomplished. We show here that strong and confined acids catalyze highly enantioselective fragmentations of a variety of cyclopropanes into the corresponding alkenes, expanding the boundaries of catalytic selective alkane activation. Computational studies suggest the involvement of the long-debated cycloproponium ions. [ABSTRACT FROM AUTHOR]

The research progress of heavy oil catalytic cracking technology at home and abroad is summarized from three aspects: the research survey of reaction mechanism of heavy oil catalytic cracking, the analysis and comparison of molecular sieve catalytic materials for heavy oil catalytic cracking, the technical characteristics and industrial application of different heavy oil catalytic cracking processes. Firstly, modified molecular sieve catalyst materials, small-crystal molecular sieves, hierarchical pore molecular sieves have become hot spots in current research and application, so as to strengthen the hydrothermal stability of catalyst, the intracrystalline diffusion and the graded cracking of heavy oil macromolecules in the hierarchical pores of the heavy oil catalytic cracking catalyst; secondly, based on the research of the carbonium ion mechanism and the free radical mechanism of the catalytic cracking reaction and the like, the reaction severity of heavy oil catalytic cracking technologies such as DCC, CPP, HCC, RTC and HSFCC is continuously improved, and in order to match the optimal reaction environment for different feeds, new reactor or multi-reactor combination technology has become the main direction of process technology research, which has achieved the purpose of improving the yield and selectivity of light olefins. [ABSTRACT FROM AUTHOR]

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Waste plastics have been regarded as a chronic environmental threat because of their disposal problem. If we do not find a sustainable technology for waste plastic conversion, it will cover the whole planet and collapse the ecosystem. Waste low-density polyethylene (LDPE) and high-density polyethylene were pyrolyzed over sol-gel derived silica–alumina (ASA) and Ti-doped silica–alumina (ASA + Ti) catalysts. The catalysts were calcined at 500 °C and characterized using different conventional techniques, e.g., XRD, FTIR, TG/DTA, SEM, EDS, and BET. Based on characterization, it can be predicted that the nanoparticles are formed of rings via Si–O–M (Al or Ti) linkages, which improved their thermal stability and catalytic activity. The polymer and catalyst were taken at an optimized ratio of 25 m m−1 in a batch reactor for degradation. The Ti-doped silica–alumina catalyst showed the maximum conversion (96%) and gasoline selectivity (45.33%) at comparatively low temperatures (376 °C). The highest specific surface area, uniform mesoporosity, and bimetallic skeleton of the Ti-doped catalyst helped to achieve the best performance. The obtained liquid product comprised both branched aliphatic and aromatic hydrocarbons. The obtained result proves that the catalytic pyrolysis of polyolefin generally advances through carbonium ions, where the catalyst acts as a Lewis acid and Lewis base consecutively. Moreover, the synthesized catalyst plays a significant role in isomerization, cyclization, and aromatization reactions. Sources of approximately 44.13 MJ of energy can be recovered from 1 kg of postconsumer waste plastic. This waste-to-fuel technology should be commercialized because it is eco-friendly and cost-effective. [ABSTRACT FROM AUTHOR]

The experiments of rapid thermal pyrolysis and catalytic pyrolysis of high density polyethylene (HDPE) were carried out using Py-GC/MS. The distribution of products of rapid pyrolysis and the influence of Fluid Catalytic Cracking catalyst on pyrolysate production were studied both qualitatively and quantitatively at the temperature of 500 °C. The corresponding reaction paths were proposed based on the experimental results. The results demonstrated that olefin production accounts for more than 70 mass% in the products of C7–C40, and remaining products were alkanes, diolefins and aromatics. At the presence of catalyst, product contents of C7–C12 increased from 16.39 to 20.59 mass%, and C33+ from 11.23 to 14.42 mass%, while C13–C32 decreased from 72.22 to 61.45 mass%. The distinctive effects of catalyst on production of monoolefine and alkane were investigated, showing that the proportion of C7–C12 increased and C13–C32 decreased. For the production of diolefin (C7–C32), however, the inhibition of catalyst was found. The thermal and catalytic pyrolysis of HDPE can be reasonably explained using free radical mechanism and carbonium ion mechanism, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ethylene yield is enhanced by the new LAS to ZSM-5 in the n -alkane cracking via exchange with Mn/Fe. • It is attributed to the differentiated adsorption of alkene/alkane and the faster C–C cleavage of monomolecular cracking. • Compared to carbenium ion pathway, carbonium ion pathway has both higher activation energy and higher activation entropy. In this work, n -octane has been selected to represent the alkane content in the naphtha for the catalytic cracking over Mn-ZSM-5 and Fe-ZSM-5 catalysts. Various characterization techniques are applied to quantify the possible active sites. The introduction of transition metal cations does not influence the strength of BAS. Therefore, the change on kinetic behavior is the contribution from newly generated LAS. Upon the elucidation of their roles in different adsorption scenarios, it is found that the new LAS establishes new adsorption equilibrium with olefin molecule formed from the thermal cracking, making the remaining alkane molecules adsorb and react on the BAS with minimum coverage of olefin. It is therefore favorable for the enhancement of ethylene yield in the primary cracking products. Furthermore, the unfavorable energy requirement of the carbonium ion pathway is compensated by the boosted activation entropy via the pathway change, as suggested by the kinetic analysis. [ABSTRACT FROM AUTHOR]

Present review outlines the advances and perspectives of computational 1H and 13C NMR applied to the stereochemical studies of inorganic, organic, and bioorganic compounds, involving in particular natural products, carbohydrates, and carbonium ions. The first part of the review briefly outlines theoretical background of the modern computational methods applied to the calculation of chemical shifts and spin–spin coupling constants at the DFT and the non‐empirical levels. The second part of the review deals with the achievements of the computational 1H and 13C NMR in the stereochemical investigation of a variety of inorganic, organic, and bioorganic compounds, providing in an abridged form the material partly discussed by the author in a series of parent reviews. Major attention is focused herewith on the publications of the recent years, which were not reviewed elsewhere. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of the excited-state properties of a large series of structurally diverse arylcarbonium derivatives that are known to be challenging for theoretical models. More specifically, we compare the pros and cons of TD-DFT (TD-M06-2X), ADC(2), and BSE/GW approaches for a large panel of compounds, using two different solvent models. Both 0-0 and vertical transition energies are considered and compared to the experimental values. All approaches reasonably reproduce the auxochromic and acidochromic shifts, although in most cases both TD-DFT and BSE/GW return larger correlation with experimental values than ADC(2) for these shifts. In contrast, the absolute transition energies obtained with ADC(2) tend to be closer to the measurements, TD-DFT using the M06-2X functional largely overestimating the experimental references (by ca. 0.5 eV), and BSE/GW providing intermediate values. In addition, we show that the selected solvent model has a significant impact on the results, the corrected linear-response approach providing larger transition energies than its linear-response counterpart. [ABSTRACT FROM AUTHOR]

[Display omitted] • The reaction network of propylene conversion under cracking conditions is detailed. • The competition relationship of different reaction pathways has been clarified. • Lowering the total acid amount can diminish the conversion of propylene. • Decreasing the acid strength effectively improves the use of carbon resources. Olefins cracking to ethylene (C 2 =) and propylene (C 3 =) on Brønsted acid sites represents a critical method for converting low-value light olefins into value-added products. In this process, a competition between propylene formation and conversion directly determined the selectivity of C 2 = and C 3 =, as well as the use of carbon resource. However, the conversion behaviour and specific reaction patterns of propylene have not been clarified. Here, we proposed a propylene conversion network under cracking conditions and demonstrated that the competition between dimerization-cracking reaction and hydrogen transfer reaction was pivotal for the use of olefin carbon resources. Hydrogen transfer index (HTI = S(C 3 H 8) / S(C 2 H 4 + C 4 H 8)) was established as a metric to assess this competitive reaction. Based on the reaction mechanism of carbonium ions, the impact of acid strength of zeolite on this competitive reaction was predicted. Furthermore, an in-depth investigation of the total acid amount and acid strength of ZSM-5 on this competition was conducted. The results indicated that an increase in acid amount enhanced hydrogen transfer reactions of propylene, and strong acid sites remarkably promoted these reactions. Specifically, an increase in the acid strength of ZSM-5 led to a more pronounced decrease in the activation energy required for hydrogen transfer reaction compared to that for dimerization-cracking reactions. Consequently, an efficient catalyst for olefin catalytic cracking to C 2 = and C 3 = is characterized by minimized strong acid sites in ZSM-5, while ensuring the cracking reaction proceeds effectively. These insights are crucial for the design of high-performance catalysts for the production of C 2 = and C 3 = from olefins. [ABSTRACT FROM AUTHOR]

A new strategy for the synthesis of 1,1‐diaryl and triarylsubstituted alkenes has been developed utilizing B(C6F5)3‐catalyzed hydroarylation of alkynes with phenols. The method provides a direct route to ortho‐alkenylated phenols with both terminal and internal alkynes. The reactions show excellent regioselectivity, and good stereoselectivity was observed for the hydroarylation of internal alkynes. Computational and experimental studies suggest that for the reaction of internal alkynes and phenols, an acid‐catalyzed isomerization mechanism involving two tertiary carbonium ion intermediates is responsible for the formation of Z‐triaryl substituted alkenes. [ABSTRACT FROM AUTHOR]

The mechanisms of dehydrogenation reactions as important processes in methanol to aromatics (MTA) have been controversial. Recent work on the active center for dehydrogenation at either Lewis acid site (LAS) or Brønsted−Lewis (B−L) acid synergistic site is a matter. The dehydrogenation processes on L−acid site (GaO+) or B−L acid site (H+ − GaO+) over GaO+/HZSM-5 with different Lewis acid locations for n -hexene to 1,5-hexadiene, as well as cyclohexene to benzene have been researched by applying the density functional theory (DFT) method. The results reflect that active center of dehydrogenation reactions is B−L acid synergistic site through B−L acid synergy mechanism. All elementary steps including C−H bond activation, the formation of H 2 , hydrogen transfer as well as the regeneration of B−acid site are easy to proceed. However, the isomerization for carbonium ions from GaO+ to skeleton oxygen of zeolites is relatively difficult. The analysis shows that isomerization is influenced by the structural and electronic properties of carbonium ions chemisorbed on zeolites. Lewis acid strength of GaO+/HZSM-5 and energy gap between HOMO and LUMO on adsorption complexes are appropriate descriptors for the C−H bond activation. The rate constants analysis indicates that increasing temperature is more favorable for C−H bond activation. Further considering that C−H bond activation occurred preferentially than isomerization, it could be a critical initial step to primarily screen catalysts. [Display omitted] • The active center of dehydrogenation is B−L acid (H+−GaO+) synergistic site. • C−H bond activation and isomerization are key processes. • Lewis acid strength and energy gap are descriptors for C−H bond activation. [ABSTRACT FROM AUTHOR]

The management of plastic waste (PW) has become an indispensable worldwide issue because of the enhanced accumulation and environmental impacts of these waste materials. Thermo-catalytic pyrolysis has been proposed as an emerging technology for the valorization of PW into value-added liquid fuels. This review provides a comprehensive investigation of the latest advances in thermo-catalytic pyrolysis of PW for liquid fuel generation, by emphasizing polyethylene, polypropylene, and polystyrene. To this end, the current strategies of PW management are summarized. The various parameters affecting the thermal pyrolysis of PW (e.g., temperature, residence time, heating rate, pyrolysis medium, and plastic type) are discussed, highlighting their significant influence on feed reactivity, product yield, and carbon number distribution of the pyrolysis process. Optimizing these parameters in the pyrolysis process can ensure highly efficient energy recovery from PW. In comparison with non-catalytic PW pyrolysis, catalytic pyrolysis of PW is considered by discussing mechanisms, reaction pathways, and the performance of various catalysts. It is established that the introduction of either acid or base catalysts shifts PW pyrolysis from the conventional free radical mechanism towards the carbonium ion mechanism, altering its kinetics and pathways. This review also provides an overview of PW pyrolysis practicality for scaling up by describing techno-economic challenges and opportunities, environmental considerations, and presenting future outlooks in this field. Overall, via investigation of the recent research findings, this paper offers valuable insights into the potential of thermo-catalytic pyrolysis as an emerging strategy for PW management and the production of liquid fuels, while also highlighting avenues for further exploration and development. [ABSTRACT FROM AUTHOR]

Carbonium ions are an important class of reaction intermediates, but their dynamic evolution is difficult to be monitored by in situ techniques under experimental conditions because of their extremely short lifetime. Probably the most famous case is 2‐norbornyl cation (2NB+): its existing form (classical or non‐classical) had been debated for decades, until the concrete proof of non‐classical geometry was achieved by X‐ray crystallographic characterization at ultra‐low temperature (40 K) and super acidic environment. However, we lack the understanding about 2NB+ at ambient conditions. Herein, by taking advantage of the confinement effect and delocalized acidic environment of zeolites, we successfully stabilized 2NB+ and unequivocally confirmed its "non‐classical" structure inside the ZSM‐5 zeolite by ab initio molecular dynamics simulations and 13C solid‐state nuclear magnetic resonance experiments. It is the first time to in situ observe the non‐classical 2NB+ without the super acidic environment at ambient temperature, which provides a new strategy to expand the carbocation chemistry. [ABSTRACT FROM AUTHOR]

Cleavage of aryl ether (Caryl–O) bonds is crucial for the conversion and value-added utilization of lignin and its derivatives, but remains extremely challenging under mild conditions due to strong Caryl–O linkages. In this study, the Caryl–O bond breaking is achieved through electrocatalytic oxidation of four phenolic lignin model compounds with typical Caryl–O bonds, i.e., 4-ethoxyphenol (EP), 4-phenoxyphenol (PP), p-benzyloxyphenol (PBP), and 2-(2-phenylethoxy)phenol (2-PEP), in a protic ionic liquid [BSO3Hmim][OTf]–H2O electrolyte, and the electrocatalytic oxidation mechanism is also fully explored. The effects of H2O on the viscosity and conductivity of the [BSO3Hmim][OTf] ionic liquid system, as well as the solubility and diffusion coefficients of O2 and the four lignin substrates, are investigated to optimize the optimal ratio of the electrolyte system composed of [BSO3Hmim][OTf] and H2O. Electrochemical oxidation–reduction behaviors of the four lignin substrates in the [BSO3Hmim][OTf]–H2O system and the effect of O2 and N2 atmospheres on degradation are studied in detail by using cyclic voltammetry (CV) curves. Finally, by combining the analysis of degradation products with isotope labeling experiments, the C–O bond cleavage mechanism is obtained, which mainly involves direct and indirect oxidation. Specifically, under a N2 atmosphere, the substrates are oxidized directly on the RuO2-IrO2/Ti mesh electrode through Caryl–O bond splitting to form quinone and carbonium ions, while under an O2 atmosphere, apart from the direct oxidation on the electrode, indirect oxidation of the lignin substrates also occurs through in situ generated H2O2. This study may provide some insight into developing effective strategies for efficient utilization of lignin under mild conditions. [ABSTRACT FROM AUTHOR]

Carbonium ion can be generated easier when low-carbon alcohols are added to hydrocracking tail oil, which initiate the cracking reaction of macromolecular n-paraffin. So the yield of lube oil base oil increases, while that of paraffin decreases, but the total yield of the two products increases. When the low-carbon alcohol is added to the raw oil for non-hydrodewaxing reaction of hydrocracking tail oil, the pour point of lubricating oil base oil declines, the flash point and the viscosity increases slightly, and the distillation range of paraffin declines slightly, but the properties of products changes little, so they can meet the actual production requirements of the factory. By examining the influence of low-carbon alcohol on the yield and properties of lubricating oil base oil and paraffin, tert-butyl alcohol is an ideal chain initiator, and the most suitable addition is 1.0 w%. [ABSTRACT FROM AUTHOR]

The formation of crystalline SiC by implantation of C ions into silicon is not a single-step process. The implantation results in an elastic distortion of the Si matrix lattice and in the formation of crystalline SiC particles, depending on ion fluence and thermal conditions during implantation and postannealing. The growth of the SiC particles in the Si matrix was studied with various synchrotron x-ray scattering techniques and high-resolution transmission electron microscopy. Crystallites of the 3C–SiC polytype are formed in a buried layer. Three groups of crystallites with different orientation relative to the Si matrix are found: with a random orientation like in a powder material, with a fiber texture axis parallel to the surface normal, and completely aligned to the Si matrix lattice due to a partially coherent growth of SiC in the Si matrix. The thermal treatment favors the growth of highly oriented material: a higher implantation temperature is more efficient than a postimplantation treatment even at higher temperatures.© 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

• The mechanism of alkene isomerizations in chabazite is investigated by DFT. • The origin of the higher rate of type A versus type B isomerization is unraveled. • Type A and B pass through loose and tight transition states respectively. • AIMD is crucial for accurate free energy calculations in zeolite. • The slow transformation between rotamers is correctly treated. Alkene skeletal isomerization elementary steps catalyzed by acid zeolites are key reactions in refining, petrochemistry and biomass conversion. We unravel the atomic-scale origin of the higher rate constant of type A isomerization (involving a direct alkyl transfer, without any change in the branching degree) than the one of type B isomerization (involving non-classical carbonium ions such as protonated cyclopropane (PCP), inducing a change in the branching degree) of C 7 carbenium ions in chabazite. Accurate free energy barriers are calculated at 300 and 500 K for both reactions by means of molecular dynamics in combination with blue moon ensemble approach, whereas the static approach is shown to fail to describe these reactions. The slow transformation between individual rotational isomers, causing non-ergodic sampling of reactant state, largely overlooked in literature, is carefully addressed in the present work. At 500 K (representative of experimental conditions), free energy barriers of 83.4 kJ/mol and 15.0 kJ/mol are determined for type B and type A isomerization respectively. The much lower barrier for type A is thus recovered, and assigned to a loose transition state, with free rotation of the migrating alkyl group, while the transition state of type B isomerization is tighter, with such a rotation blocked, due to the simultaneous hydride shift taking place on the edge of the PCP. [ABSTRACT FROM AUTHOR]

The infrared spectra for the molecular hydrogen-solvated carbonium ions, CH+5(H2)n (n=1–6) in the frequency range of 2700–4200 cm-1 are presented. Spectroscopic evidence was found in support of the scrambling of CH+5 through the large amplitude motions such as the CH3 internal rotation and the in-plane wagging motion of three-center two-electron bond. More importantly, the scrambling motions of CH+5 cores were slowed down considerably by attaching the solvent H2 molecules to the core ion. The complete freezing of the scrambling motions was found when the first three H2 molecules were bound to the CH+5 core. A good agreement between the experimental and the theoretical predictions was found in the dynamics of CH+5. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The closely related Cs(1), Cs(2), and C2v(3) structures of CH5+ have been reinvestigated with high level ab initio theory through the coupled cluster with single and double substitutions (CCSD), and CCSD with perturbatively included connected triple excitations [CCSD(T)] levels, employing a triple-ζ plus double polarization functions basis set, with f-functions on carbon as well as d-functions on the hydrogens [TZ2P(f,d)]. Vibrational frequencies have been computed up to TZ2P+f CCSD; the inclusion of f-functions on carbon is critical for the configuration interaction with single and double excitations (CISD) and coupled cluster methods using the triple-ζ basis sets. The changes in geometries between the CISD and CCSD levels are very small, e.g., the C–H bond lengths vary by at most 0.005 Å. Thus, the optimizations are essentially converged within theoretical limits. The differences in energies of 1, 2, and 3 decrease and essentially vanish at the most sophisticated levels when the zero point vibrational energy corrections are applied. Hence, there is essentially no barrier to complete hydrogen scrambling. [ABSTRACT FROM AUTHOR]

Investigates the formation mechanisms of C[sub 1][sup +], C[sub 2][sup +], and C[sub 3][sup +] ions by laser ablation of graphite. Use of time-of-flight quadrupole mass spectroscopy; Effect of laser ablation on the formation of small carbon cluster ions; Recombination of carbon atoms and subsequent ionization.

CHO+ ions are made by electron impact on CD3OH in the source (ICR1) of a tandem ion cyclotron resonance spectrometer. These ions are injected into a differentially pumped analysis cell (ICR2) where they are reacted with a number of small molecules. The internal energy distribution in the CHO+ ions is obtained using total reactivity studies with neutral molecules of varying proton affinities. About 40% of the CHO+ ions react with D2 either by proton transfer to form D2H+ or isotopic exchange to form CDO+ ions. A series of experiments are performed that conclusively show these ions are the HOC+ isomer and the exchange is due to the catalytic isomerization reaction HOC++D2→DCO++HD which is approximately 37 kcal/mol exothermic. The product DCO+ ions are vibrationally cool indicating the reaction releases most of its energy as kinetic energy. Absolute rate constants for reactions of CHO+ ions with the neutrals 13CO, 15N2, CO2, O2, D2, and Ar are reported. HOC+ reacts with D2 at about 30% of the collision rate. This rate decreases with increasing HOC+ kinetic energy in the range 0.025 to 0.44 eV. The two products of the reaction are D2H+/CO and DCO+/HD with DCO+/HD comprising ∼42% of the products for the HOC+ ions formed from CD3OH. Phase space theory calculations are performed to determine the barrier to catalytic isomerization. The data are best fit with a barrier between 0.0 and -0.05 eV relative to the HOC+/D2 asymptotic energy. A barrier of this magnitude yields reaction rate constants at interstellar temperatures of at least 10% of the collision rate constant (i.e., k>1×10-10 cm3/s), and could explain why so little HOC+ is observed in interstellar clouds. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZSM-5 zeolites were synthesized by employing various OSDAs and Na cations. • Regionally spatial framework Al distributions in MFI channels are investigated. • Framework Al distributions intensely control n-butane cracking reaction pathways. • Framework Al sited in straight or intersection channels favors propylene production. The regulation of the engineering regionally spatial framework aluminum (Al F) distribution in MFI channels has been considered as an effective way for the production of light olefins by targeted fluid catalytic cracking (TCO) technology. In this work, ZSM-5 zeolites with controlled Al F distributions are facilely synthesized by tuning the combinations of pentaerythritol (PET), tetrapropylammonium (TPA) and Na cations. The Al F atoms in the prepared HZ5-[PET + Na] and HZ5-[TPA] samples are enriched in the straight channels and intersection channels, respectively, which are favorable to the n-butane monomolecular reaction pathway, promoting the propylene production. Whereas the Al F atoms in the HZ5-[TPA + Na] sample are simultaneously distributed in both the straight and intersection channels, the n-butane molecules preferentially take place monomolecular reaction in the straight channels to generate carbonium ions (e.g., C 2 H 5 +, C 3 H 7 + and C 4 H 9 +). Subsequently, all of them enter into the intersection channels to induce the occurrence of bimolecular reaction. Such a process is conducive to the formation of ethylene. These insights can help to clarify the catalytic behavior of regional framework acid sites in ZSM-5 channels and then provide an effective approach to design efficient TCO catalysts. [ABSTRACT FROM AUTHOR]

Cyclohexane is converted into nonclassical five-coordinated carbonium ion (B), which easily undergo open-ring, and then cracking, skeletal isomerization, β-cleavage, H-transfer, and dehydrogenation into alkenes and H 2. The primary products contain ethylene, propylene, and butene in the reaction of cyclohexane cracking, and some of them could further convert to other products. Ethylene could also be formed by secondary reactions. [Display omitted] • CL-ROC avoids the potential hazard and achieve much safer and energy saving. • Up to 57.52% olefin yield was achieved with extremely low CO x yield of 0.28%. • Li 2 CO 3 surface promoter inhibits lattice oxygen excess conduction and evolution. • The roles of core and shell for catalytic CL-ROC reaction scheme was revealed. Oxidative cracking is a promising process to reduce the energy and carbon intensities for light olefins production by combing catalytic oxidation and cracking reactions. This work reports an efficient redox oxidative cracking (ROC), which could avoid the potential hazard of co-feed oxygen with hydrocarbons and save the air separation process in an oxidative cracking process to achieve a much safer reaction process and more energy saving. Highly efficient redox catalysts, i.e. composites of the Li 2 CO 3 promoted perovskite oxides (La 0.8 Sr 0.2 FeO 3 and CaMnO 3), were applied in ROC of naphtha by using a model compound of cyclohexane. Among the catalysts, La 0.8 Sr 0.2 FeO 3 @Li 2 CO 3 exhibits excellent ROC performance (57.52 % yield of olefins and extremely low CO x yield of 0.28 %), and it demonstrates high structural stability and cycling ability as well. The olefins yield in this work increased by > 19 % compared to conventional non-oxidative catalytic cracking (38 % yield of olefins), and the CO x yield also decreased from 18 % to extremely low of 0.28 % compared with the best-reported O 2 -cofeed cyclohexane oxidative cracking. The characterization results indicated that La 0.8 Sr 0.2 FeO 3 @Li 2 CO 3 attributed to being a core–shell structure with a La 0.8 Sr 0.2 FeO 3 core covering with a molten Li 2 CO 3 layer. Further characterization indicates that the modification of Li 2 CO 3 affected the migration rate of oxygen and inhibited the excessive oxidation of olefins, which enhancing the selectivity of light olefins and inhibits CO x formation. The oxygen migration rate of LSF is 5.81 × 10−11 mol/(g·s) compared with 3.37 × 10−11 mol/(g·s) of LSF@20 %Li. These findings offer a new strategy to design effective redox catalysts for redox oxidative cracking. [ABSTRACT FROM AUTHOR]

The alkylation kinetics of isobutane with 2-butene catalyzed by composite ionic liquid (CIL) was investigated with batch experiments. The optimized reaction time of CIL-catalyzed alkylation was found to be less than 30 s, much shorter than the traditional H 2 SO 4 -catalyzed one. Based on the carbonium ion mechanism, the kinetic model was further established, in which the concentration profiles of three groups of key components in alkylates with time can be well predicted, i.e. trimethylpentane (TMPs), dimethylhexanes (DMHs) and heavy ends (HEs). The rate constant related to the formation of TMPs in the CIL alkylation is more than two orders of magnitude larger than that in the H 2 SO 4 alkylation. The enhancement of the rate constants for the CIL alkylation at the macroscopic scale can be ascribed into the higher solvation and diffusion of isobutane in the CIL at the microscopic scale, which is confirmed by the solvation free energy and diffusion coefficient calculation using molecular dynamics simulation. Hopefully, the multi-scale information in this work can bring novel insights into the understanding of CIL-catalyzed alkylation and further the design and optimization of this process. [ABSTRACT FROM AUTHOR]

To understand the alkylation mechanism of isobutane with butene, it is of great importance to elucidate the difference of protonation behaviours among butene isomers at molecular scale, because it is the starting point of this reaction. Herein, we have calculated the protonation processing of isobutene and 2-butene on a 120T HY cluster model, using an embedded QM/MM (quantum mechanical/molecular mechanical) method. The formation energy of p-complex from isobutene is higher than that of 2-butene owing to the effect of electronic interaction and steric hindrance between the C=C bond of butene and the H atom of the HY zeolite. Moreover, the energy of t-butyl alkoxide (TBA) produced via isobutene protonation is higher than that of s-butyl alkoxide (SBA) from 2-butene, as the C-O bond of TBA is longer. In addition, the transition state of isobutene protonation is a t-butyl carbonium ion, while the corresponding structure during 2-butene protonation is a s-butyl carbonium ion, which is less stable. In conclusion, isobutene is much easier to be activated by Brönsted acid site of HY zeolite than 2-butene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of acid strength on butene isomerization mechanisms was studied. • Relationship among acid strength, type of butene, and alkylate quality was clarified. • Stability of butyl cations follows the order: tert -cation > cis -cation > trans -cation. • 1-butene and 2-butene as reactant have similar alkylation activity on strong acids. • Skeleton isomerization is more difficult to occur than the other two isomerization. Understanding the effect of acid strength on butene isomerization mechanisms is essential in C4 alkylation process. Herein, the double bond, trans-cis, and skeleton isomerization mechanisms of butene over acid sites with different acid strengths were investigated utilizing density functional theory (DFT) calculations. It is demonstrated that the acid strength significantly affects the isomerization mechanisms of butene. The stability of carbonium ions as reaction intermediates follows the order: tert -butyl cation > cis -butyl cation > trans -butyl cation, which is more sensitive to acid strength than that of butoxide species. Therefore, the reaction pathways of double bond and trans-cis isomerizations changed with varying the acid strength. Based on the analysis of activation energy barriers, it is found that 1-butene and 2-butene can be easily converted into each other over strong acid site. Thus, for reactants, C4 alkylation has no selectivity to 1-butene and 2-butene over strong acid site, which is consistent with experimental study. This work provides mechanistic insights into the relationship among acid strength, type of butene, and quality of alkylate in the C4 alkylation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • With the TU additive, the Zn-S battery shows excellent cycle performance. • TU− can accelerate the crack of Zn-S bonds to improve the conversion from ZnS to S. • ZnS reacts with Met+ much faster than H 2 O, inhibiting the formation of SO 4 2−. Aqueous zinc-sulfur (Zn-S) battery has attracted much attention due to the ultrahigh theoretical capacity of S (1675 mA h g−1). Nevertheless, its lifespan is far from satisfactory owing to the sluggish reaction kinetics for ZnS conversion to S, and the formation of irreversible by-product of SO 4 2− during charging. Herein, a novel bifunctional electrolyte additive thiourea (TU) was introduced to solve the above problems. It has been found that TU can undergo reversible redox reactions during cycles, which not only enhances the reversibility between ZnS and S but also contributes to extra capacities. Based on the ex-situ FTIR and XPS characterization, in combination with the electrochemical performance of thiourea and its derivatives, the influential mechanism of TU on the S@KB electrode was proposed. Its negative centers and positive centers of the intermediates can interact with ZnS to weaken the Zn-S bonds to improve the electrochemical dynamics. Simultaneously, the carbonium ions in the intermediate of TU show strong reactivity to ZnS so that the formation of SO 4 2− can be inhibited. As a result, the S@KB electrode shows excellent cyclic performance with 763.7 mA h g−1 capacity after 300 cycles at 5 A/g, corresponding to a low decay rate of only 0.11 % per cycle. This work provides a promising electrolyte additive and an effective strategy to improve the reaction kinetics and cycle stability of Zn-S batteries. [ABSTRACT FROM AUTHOR]

Under hydrothermal environments covering the subcritical and supercritical regions of water, the involvement of the carbonium mechanism in the dealkylation of aromatics and its resulting influence on the pyrolysis of heavy oil were surveyed. α-Olefin groups, as either a part of straight chain hydrocarbons or the terminal of alkyl substitutes of aromatics, are protonated spontaneously by hydronium ions into carboniums, followed by β-scission with similar reaction kinetic characteristics. The probability of the protonation of α-olefins under hydrothermal environments depends on the ionic product of water, so the occurrence of the β-scission in the carbonium mechanism is related to the thermodynamic state of water. With the aid of the carbonium mechanism at increasing water density, a recovered conversion rate and an increasing ratio of propene to ethylene in the product occur during the pyrolysis of a model α-olefin of dodecene under hydrothermal environments. Also, the dealkylation involved in the pyrolysis of maltenes is accelerated. [ABSTRACT FROM AUTHOR]

For widespread use of rotating gantries for carbon radiotherapy, we designed a new compact gantry. This new gantry consists of three combined-function superconducting magnets having a bending angle of 90°. The dipole field of the superconducting magnets is set to be B\max=5.02 T, corresponding to a bending radius of 1.32 m for transporting carbon ions having kinetic energy of 430 MeV/u. The superconducting magnet also has three independent superconducting quadrupole coils, which are to be wound inside the dipole coil for beam focusing. The dipole and quadrupole coils are electrically isolated in the magnet and connected to independent power supplies so that each field component can be independently excited. Having used the combined-function superconducting magnets, the size of the rotating gantry would become very compact; the length and radius are 5.1 and 4.0 m, respectively. The magnetic field distributions of the superconducting magnets were calculated with a 3-D electromagnetic field solver, Opera-3d code. With calculated fields, the superconducting coils were designed to obtain uniform field distributions. In this paper, the design of this compact rotating gantry and the superconducting magnets is presented. [ABSTRACT FROM PUBLISHER]

In the search for tricarbaporphyrinoids, a three-component acid-catalyzed condensation of azulene, 2,5-bis[( p-tolyl)hydroxymethyl]thiophene, and an aryl aldehyde has been elaborated, affording the appropriate thiatriazuliporphyrinogens. The subsequent oxidation yielded a rare example of a macrocyclic organic tetracation, which can be readily and reversibly converted into macrocyclic tri- and dicarbocations by addition of one or two hydroxides bound at the meso position(s). Further insight into the influence of carbocation formation on the geometry, electronic structure, and magnetic manifestation in 1H NMR spectroscopy has been obtained by using density functional theory calculations. The charge distribution was evaluated by mapping electron density surfaces with electrostatic potential (ESP). [ABSTRACT FROM AUTHOR]

Astrophysically observed extraterrestrial molecular matter contains, besides hydrogen and water, methane and methanol as the most abundant species. Feasible pathways and chemical aspects of their formation as well as of derived hydrocarbon homologues and their ions (carbocations and carbanions) are discussed on the basis of observed similarities with our studied terrestrial chemistry. The preferred pathway for converting extraterrestrial methane according to Ali et al. is based on CH5+ and Olah's related nonclassical carbonium ion chemistry. On the basis of the observed higher reactivity of methanol compared with methane in various chemical reactions, a feasible new pathway is proposed for the conversion of extraterrestrial methanol to hydrocarbons, their derivatives, and carbocations together with a possible connection with methonium ion-based chemistry. [ABSTRACT FROM AUTHOR]

Ab initio calculations for the protonation of the C-H and C-C bonds of methane, ethane, propane and isobutane by a superacid moiety was carried out. For the C-H protonation (H/H exchange) the transition state resembles an H-carbonium ion coordinated with the superacid. The activation energy for the H/H exchange was about 16 kcal.mol-1, at B3LYP/6-31++G** + RECP (Sb) level, regardless the type of C-H bond being protonated. For the C-C protonation the activation energy depends on the structure of the hydrocarbon and was always higher than the activation energy for C-H protonation, indicating a higher steric demand.

A diazonium ion derived from 18-aminoandrostane rearranged upon decomposition by a carbonium and a carbenium ion to furnish a mixture of a cyclopropanated compound and two D- homo-androstenes. Hydrogenation of this mixture gave the saturated hydrocarbons, 18- nor- D- homo-androstane and 5α,14β-androstane, which are both fossil sterane biomarkers in Neoproterozoic crude oil. The so far unknown constitution and configuration as well as the geochemical genesis were established by this experiment. The starting material for this investigation, 18-aminoandrostane, was prepared in twelve steps from androstan-17-one (12.5 % overall yield) with a Barton reaction as the key step. [ABSTRACT FROM AUTHOR]

The discovery of carbocations and carbanions by Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) instruments onboard the Cassini spacecraft in Titan׳s upper atmosphere is truly amazing for astrochemists and astrobiologists. In this paper we identify the reaction mechanisms for the growth of the complex macromolecules observed by the CAPS Ion Beam Spectrometer (IBS) and Electron Spectrometer (ELS). This identification is based on a recently published paper (Ali et al., 2013. Planet. Space Sci. 87, 96) which emphasizes the role of Olah׳s nonclassical carbonium ion chemistry in the synthesis of the organic molecules observed in Titan׳s thermosphere and ionosphere by INMS. The main conclusion of that work was the demonstration of the presence of the cyclopropenyl cation – the simplest Huckel׳s aromatic molecule – and its cyclic methyl derivatives in Titan׳s atmosphere at high altitudes. In this study, we present the transition from simple aromatic molecules to the complex ortho-bridged bi- and tri-cyclic hydrocarbons, e.g., CH 2 + mono-substituted naphthalene and phenanthrene, as well as the ortho- and peri-bridged tri-cyclic aromatic ring, e.g., perinaphthenyl cation. These rings could further grow into tetra-cyclic and the higher order ring polymers in Titan׳s upper atmosphere. Contrary to the pre-Cassini observations, the nitrogen chemistry of Titan׳s upper atmosphere is found to be extremely rich. A variety of N-containing hydrocarbons including the N-heterocycles where a CH group in the polycyclic rings mentioned above is replaced by an N atom, e.g., CH 2 + substituted derivative of quinoline (benzopyridine), are found to be dominant in Titan׳s upper atmosphere. The mechanisms for the formation of complex molecular anions are discussed as well. It is proposed that many closed-shell complex carbocations after their formation first, in Titan׳s upper atmosphere, undergo the kinetics of electron recombination to form open-shell neutral radicals. These radical species subsequently might form carbanions via radiative electron attachment at low temperatures with thermal electrons. The classic example is the perinaphthenyl anion in Titan׳s upper atmosphere. Therefore, future astronomical observations of selected carbocations and corresponding carbanions are required to settle the key issue of molecular anion chemistry on Titan. Other than earth, Titan is the only planetary body in our solar system that is known to have reservoirs of permanent liquids on its surface. The synthesis of complex biomolecules either by organic catalysis of precipitated solutes “on hydrocarbon solvent” on Titan or through the solvation process indeed started in its upper atmosphere. The most notable examples in Titan׳s prebiotic atmospheric chemistry are conjugated and aromatic polycyclic molecules, N-heterocycles including the presence of imino >C N–H functional group in the carbonium chemistry. Our major conclusion in this paper is that the synthesis of organic compounds in Titan׳s upper atmosphere is a direct consequence of the chemistry of carbocations involving the ion–molecule reactions. The observations of complexity in the organic chemistry on Titan from the Cassini–Huygens mission clearly indicate that Titan is so far the only planetary object in our solar system that will most likely provide an answer to the question of the synthesis of complex biomolecules on the primitive earth and the origin of life. [ABSTRACT FROM AUTHOR]

Glycosylation of 6 α,12 β-dihydroxy-20 R,25-epoxydammaran-3-one (panaxatriol 3-ketone, 2) under Koenigs-Knorr reaction conditions and the Helferich modification was studied. Condensation of 2 with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylbromide ( 5) in the presence of AgO and 4-Å molecular sieves in CHCl gave acetylated 6 α,12 β-dihydroxy-20 R,25-epoxydammaran-3-one 12- O-β-D-glucopyranoside whereas in the presence of Hg(CN) in nitromethane at 25°C the tetrahydropyran ring opened and, depending on the ratio of reagents, acetylated 12-, 12,25-di-, or 6,12,25-tri -O-β-D-glucopyranosides of 6 α,12 β,25-trihydroxydammar-20(22) E-en-3-one formed. 6 α,12 β-Dihydroxy-20 R,25-epoxydammaran-3-one 12- O-β-D-glucopyranoside and 12-, 12,25-di-, and 6,12,25-tri- O-β-D-glucopyranosides of 6 α,12 β,25-trihydroxydammar-20(22) E-en-3-one were synthesized for the first time. [ABSTRACT FROM AUTHOR]

In this article, an environmentally friendly non-noble-metal class of Cs-Ni 2 P/active carbon (AC) catalyst was prepared and demonstrated to exhibit enhanced catalytic performance in isobutane dehydrogenation. The results of activity tests reveal that Ni/AC catalyst was highly active for isobutane cracking, which led to the formation of abundant methane and coke. After the introduction of phosphorus through impregnation with ammonium di-hydrogen phosphate and H 2 -temperature programmed reduction, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene and stability of catalyst increased remarkably. The characterization results indicate that, after the addition of phosphorous, the improvement of dehydrogenation selectivity is ascribed to the partial positive charges carried on Ni surface in Ni 2 P particles, which decreases the strength of Ni C bond between Ni and carbonium-ion intermediates and the possibility of excessive dehydrogenation. In addition, Cs-modified Ni 2 P/AC catalysts display much higher catalytic performance as compared to Ni 2 P/AC catalyst. Cs-Ni 2 P-6.5 catalyst has the highest catalytic performance, and the selectivity to isobutene higher than 93% can be obtained even after 4 h reaction. The enhancement in catalytic performance of the Cs-modified catalysts is mainly attributed to the function of Cs to improve the dispersion of Ni 2 P particles, transfer electron from Cs to Ni, and decrease acid site number and strength. [ABSTRACT FROM AUTHOR]

C(CH3)5+ is the first reported example of a five-coordinate carbon atom bound only to separate (that is, monodentate) carbon ligands. This species illustrate the limits of carbon bonding, exhibiting Lewis-violating 'electron-deficient bonds' between the hypercoordinate carbon and its methyl groups. Though not kinetically persistent under standard laboratory conditions, its dissociation activation barriers may permit C(CH3)5+ fleeting existence near 0 K. [ABSTRACT FROM AUTHOR]

The condensation of lignin under acidic conditions inhibited the subsequent value-added utilization of lignin, and the condensed lignin covered the biomass surface. Here, a method of benzenesulfonic acid pretreatment combined with nucleophilic reagents promoted pyrolytic saccharification and lignin hydrogenation was reported. The anhydrosugar content in the pyrolysis bio-oil increased from 66.91% to 69.00%, 72.88%, and 72.16% via adding methanol, propionaldehyde, 3-hydroxylic-2-naphthoic acid, respectively. The characterization of the biomass surface structure and the calculation of bond lengths indicated that carbonium ions prefer to bind with the added nucleophilic reagent rather than the lignin fragment. Furthermore, the quenching of the carbonium ions preserved the β-O-4 bond, as demonstrated in 2D NMR. In the subsequent hydrogenation reaction, it was found that methanol facilitated the production of lignin monomer. The calculation also revealed that the quenching of the carbonium ions with methanol reduced the bond-breaking energy of the β-O-4 bond., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Abstract: Host–guest complexation between crown ether-based cryptand hosts and a carbonium ion, tropylium hexafluorophosphate was studied. 1H NMR, NOESY NMR, and electrospray ionization mass spectrometry were employed to characterize these inclusion complexes. The contrast tests of 1H NMR and association constants indicated that cryptands are much better hosts for tropylium hexafluorophosphate than the corresponding simple crown ethers. C–H⋯O hydrogen bonding, face-to-face π-stacking interactions, and charge-transfer interactions are thought to be the main driving forces for the formation of these host–guest complexes. These multiple non-covalent interactions may jointly contribute to the complex formation and considerably reinforce the complex stability. Moreover, the complexation between dibenzo-24-crown-8-based cryptand 4 and tropylium hexafluorophosphate 7 can be reversibly controlled by adding KPF6 and then DB18C6 in 1:1 acetonitrile/chloroform, providing a new cation-responsive host–guest recognition motif for supramolecular chemistry. [Copyright &y& Elsevier]

Absolute cross sections for electron impact single and multiple ionization of C+, N+ and O+ ions leading to the formation of Cq + (q = 2–4), Nq + (q = 2–5) and Oq + (q = 2–5) are reported. The animated crossed beam method is applied in the energy range extending from the respective thresholds up to 2.5 keV. The concerned target ions belong to the second row of the periodic table, with configurations 2s22px (x = 1–3). The maximum cross sections for the multiply charged products Cq + are found to be in the range from 2.3× 10−20 cm2 (for C4 +) up to 6.3× 10−17 cm2 (for C2 +); for Nq + they range from 3.0× 10−22 cm2 (for N5 +) up to 5.1× 10−17 cm2 (for N2 +) and, lastly, for Oq + they range from 5.5× 10−22 cm2 (for O5 +) up to 5.2× 10−17 cm2 (for O2 +). The corresponding threshold energies are found to be in satisfactory agreement with spectroscopic values. The general feature of the measured cross sections is investigated. Their values for single ionization are reasonably explained by the calculations using the Coulomb–Born approximation with exchange, while those for multiple ionization are found to agree well with the semiempirical model for q = 3, but they appear to be notably overestimated by a semiempirical Bethe–Born-type formula when q > 3. [ABSTRACT FROM AUTHOR]

Carbonium-ionic heterogeneous catalytic reactions over acid zeolites are accompanied with coke formation which blockades the active sites and obeys periodical regeneration of catalysts. Recently the oscillatory movement of coke deposits alternatively in the direction or onto the external surface of zeolite crystals or into the porous structure of the latter has been observed. It causes the oscillatory proceeding of carbonium-ionic reactions and favours the prolongation of catalyst work before regeneration enhancing its productivity. The availability of the top deactivation limit, after achieving the latter the oscillatory dynamics of coke movement absences, has been revealed. It is supposed that the following rapid catalyst's activity loss is connected with the achievement of the mentioned limit. The availability of the bottom deactivation depth, when oscillatory alternative coke movement absences, is substantiated too. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-two tons of catalyst was used in the 130kt/a industrial PX device at Sinopec Qilu Company for removing trace olefins from aromatics. The result showed it had an effective running time about 3 times as long as that of the commercial clay. The reaction mechanism was explored and it indicated that the weak L acid was the main reason for the enhancement of the catalyst activity. In addition, the process of the olefins reacted with the aromatics via the carbonium ion mechanism can be generalized by the alkylation reaction. [Copyright &y& Elsevier]

Goodlinear correlations between GIAO–CCSD(T) calculated 11B NMR chemical shifts of hypercoordinate boronium 1–6band borenium 7–9bionsand 13C NMR chemical shifts of the correspondingisoelectronic carbonium 1–6aandcarbenium 7–9aions, respectively,were found. [ABSTRACT FROM AUTHOR]