Targeted Catalytic Cracking to Olefins(TCO):Reaction Mechanism,Production Scheme,and Process Perspectives

Light olefins are important organic building blocks in the chemicals industry.The main low-carbon olefin production methods,such as catalytic cracking and steam cracking,have considerable room for improvement in their utilization of hydrocarbons.This review provides a thorough overview of recent studies on catalytic cracking,steam cracking,and the conversion of crude oil processes.To maximize the production of light olefins and reduce carbon emissions,the perceived benefits of various technologies are examined.Taking olefin generation and conversion as a link to expand upstream and downstream processes,a targeted catalytic cracking to olefins(TCO)process is proposed to meet current demands for the transformation of oil refining into chemical production.The main innovations of this process include a multiple feedstock supply,the development of medium-sized catalysts,and a diameter-transformed fluidizedbed reactor with different feeding schemes.In combination with other chemical processes,TCO is expected to play a critical role in enabling petroleum refining and chemical processes to achieve low carbon dioxide emissions.

Covalent organic framework shows high isobutene adsorption selectivity from C_(4) hydrocarbons:Mechanism of interpenetration isomerism and pedal motion

Adsorption and separation of C_(4) hydrocarbons are crucial steps in petrochemical processes.Employment of porous materials for enhancing the separation efficiency have paid much attention.Covalent-organic frameworks of diamond-topology,dia-COFs,often exhibit unique structural properties such as interpenetration isomerism and pedal motion.Herein,in order to get a deep insight into the structure-performance correlation of such dia-COFs,a series of dia-COF materials have been proposed and theoretically investigated on the C_(4) separation.It is found that these dia-COFs display an excellent adsorption and separation property towards isobutene with respect to other C_(4) hydrocarbons(i.e.,1,3-butadiene,1-butene,2-cis-butene,2-trans-butene,isobutane and n-butane).What’s more,the correlation between the topology parameters and experimental synthesis feasibility has been established for COF-300(dia-cN),and the unreported COF-300(dia-c3) is predicted to be experimentally feasible synthesized.Our findings not only provide a deep insight into the mechanism of topology characteristics of dia-COFs on C_(4) adsorption and separation properties but also guide the design and synthesis of novel highly-effective porous materials.

Special Issue for Zeolite Catalysis

As the most successful heterogeneous catalyst,zeolite has found widespread application in methanol to olefins,alkane dehydrogenation,CO_(2)hydrogenation,syngas conversion,and various other processes.To provide a comprehensive understanding of the structure-performance relationship,a series of fundamental papers have been published in this special issue,covering topics ranging from zeolite synthesis to structural and acidic characterization,and catalytic reactions.

Modulation of zeolite surface realizes dynamic copper species redispersion

Zeolite-based metal nanoparticles(NPs)catalysts have shown promising applications in fuel production,petro-and fine-chemical manufacture,biomass refinery,and so on.Modulation of hydroxyl groups on the zeolite surface has proven to be effective in boosting catalytic reactions over metal-zeolite catalysts.For example,modifying the wettability of ZSM-5 and titanium silicalite-1(TS-1)crystals by surface hydrophobization drastically enhances catalytic performance of zeolites encapsulated AuPd[1]and Pt[2]NPs in methane oxidation and aldehydes/ketones hydrogenation,respectively.In fact,two kinds of hydroxyl groups are present in zeolite materials,which refers to bridged hydroxyls[Si-O(H)-Al]and silanols[Si-O(H)].Both hydroxyl groups are defects of zeolite framework structures,which provides anchor points in dispersing metals[3].The former hydroxyl group is tunable to control acidity by adjusting Si/Al ratio in zeolite,whereas the role of silanols is not fully understood[4],particularly in the dispersion of metal NPs.

Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement

Developing efficient and stable zeolites for vapor-phase Beckmann rearrangement of cyclohexanone oxime is still a great challenge to realizeε-caprolactam(CPL)green production.In this work,the hierarchical porous silicalite-1 zeolites with multiple hollow structure(S-1-M)are explored by in-situ desilication−recrystallization post-treatment of spongy highway-like zeolites(S-1-S),which are synthesized through silanization synthesis of conventional bulky silicalite-1(S-1).Compared to S-1,S-1-M achieves superior catalytic performance,with improving the CPL selectivity from 85.7%to 94.1%and prolonging the catalyst lifetime from 74 to 126 h at a weight hourly space velocity(WHSV)of 6 h^(−1).Comprehensive physiochemical studies demonstrate that the highly dispersed intracrystalline cavities within S-1-M endow greater mass diffusion and better quasi acidity inducing by the enhanced H-bonds among abundant H-bonded silanols,which is cooperatively responsible for its superior catalytic performance.

High population and dispersion of pentacoordinated Al~Ⅴ species on the surface of ?ame-made amorphous silica-alumina

Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely observed in conventionally prepared silica-alumina.Here,we show that high population and dispersion of Al~Ⅴ species on the surface of amorphous silica-alumina(ASA)can be achieved by means of flame spray pyrolysis.High resolution TEM/EDX,high magnetic-field NMR and DFT calculations are employed to characterize the structure of as-prepared ASAs.Solid-state ^(27)Al multi-quantum MAS NMR experiments show that most of the Al~Ⅴspecies are formed independently from the alumina phase and are accessible for guest molecules on the surface.Upon water adsorption,these Al~Ⅴ species are transformed to Al~Ⅵ species,structurally similar to surface Al~Ⅳ species,as confirmed by DFT calculations.The outstanding catalytic activity of as-synthesized ASA is demonstrated using the in situ H/D exchange reaction with deuterated benzene as an example.The Al~Ⅴ-rich ASA provides a much lower activation energy(～30 kJ/mol)than that reported for zeolite H-ZSM-5(～60 kJ/mol).The superior catalytic performance is attributed to the high Al~Ⅴcontent promoting the surface active sites in ASA.The knowledge gained on the synthesis of Al~Ⅴ-rich ASAs and the nature of aluminum coordination in these materials could pave the way to more efficient silica-alumina based catalysts.

A single Au nanoparticle anchored inside the porous shell of periodic mesoporous organosilica hollow spheres

An ideal metal catalyst requires easy contact with reaction reagents, a large number of exposed active sites, and high stability against leaching or particle agglomeration. Anchoring a metal core inside a porous shell, though scarcely reported, may combine these advantages owing to the integration of the conventional supported metal arrangement into a core@void@shell architecture. However, achieving this is extremely difficult owing to the weak core-shell affinity. Herein, we report, for the first time, an approach to overcome this challenge by increasing the core-shell interaction. In this regard, we synthesized a novel Au@void@periodic mesoporous organosilica （PMO） architecture in which a single Au core is firmly anchored inside the porous shell of the hollow PMO sphere. The non-covalent interactions between the poly（vinylpyrrolidone） （PVP） groups of functionalized Au and ethane moieties of PMO facilitate the movement of the Au core towards the porous shell during the selective alkaline etching of Au@SiO2@PMO. Shell-anchored Au cores are superior to the suspended cores in the conventional Au@void@PMO in terms of contact with reagents and exposure of active sites, and hence show higher catalytic efficiency for 4-nitrophenol reduction. The methodology demonstrated here provides a new insight for the fabrication of versatile multifunctional nanostructures with cores anchored inside hollow shells.

Functional groups to modify g-C3N4 for improved photocatalytic activity of hydrogen evolution from water splitting

Rational modification by functional groups was regarded as one of efficient methods to improve the photocatalytic performance of graphitic carbon nitride(g-C3 N4).Herein,g-C3 N4 with yellow(Y-GCN)and brown(C-GCN)were prepared by using the fresh urea and the urea kept for five years,respectively,for the first time.Experimental results show that the H2 production rate of the C-GCN is 39.06μmol/h,which is about 5 times of the Y-GCN.Meantime,in terms of apparent quantum efficiency(AQ.E)at 420 nm,C-GCN has a value of 6.3%and nearly 7.3 times higher than that of Y-GCN(0.86%).The results of XRD,IR,DRS,and NMR show,different from Y-GCN,a new kind of functional group of—N=CH—was firstly in-situ introduced into the C-GCN,resulting in good visible light absorption,and then markedly improving the photocatalytic performance.DFT calculation also confirms the effect of the—N=CH—group band structure of g-C3N4.Furthermore,XPS results demonstrate that the existence of—N=CH—groups in C-GCN results in tight interaction between C-GCN and Pt nanoparticles,and then improves the charge separation and photocatalytic performance.The present work demonstrates a good example of"defect engineering"to modify the intrinsic molecular structure of g-C3N4 and provides a new avenue to enhance the photocatalytic activity of g-C3N4 via facile and environmental-friendly method.

Anionic Tuning of Zeolite Crystallization

Zeolites are of great industrial relevance as catalysts,adsorbents,and ion-exchangers and typically synthesized under hydrothermal conditions.Rational regulation of their crystallization process is of great significance for zeolite production.In this work,we systematically investigate the role of anions in tuning zeolite crystallization via anion introduction including SO_(4)^(2−),F^(−),Cl^(−),Br^(−),I^(−),and SCN^(−) in the sodium form into the SiO2-TPAOH-H2O[tetrapropylammonium hydroxide(TPAOH)]synthetic system of silicalite-1 zeolite.