Optimizing zeolite stabilized Pt-Zn catalysts for propane dehydrogenation

Propane dehydrogenation(PDH)provides an alternative route to non-petroleum based propylene and eligible catalysts with good overall performance are still being explored.Herein,we report the construction of zeolite stabilized Pt-Zn catalysts Pt-Zn/Si-Beta for PDH.Characterization results from transmission electron microscopy(TEM),ultraviolet-visible(UV-vis)and Fourier transform infrared(FTIR)spectroscopy reveal that highly-dispersed Zn species are stabilized by the silanols from zeolite framework dealumination,which then act as the anchoring sites for Pt species.The close contact between Pt-Zn species and the electronic interaction thereof make Pt-Zn/Si-Beta robust PDH catalysts.Under optimized conditions,a high propylene production rate of 4.11 molmol_(Pt)^(-1)s^(-1),high propylene selectivity of 98% and a sustainable deactivation rate of~0.02 h^(-1)can be simultaneously achieved at 823 K.Coke deposition is not the key reason for the catalytic deactivation,while the loss of Zn species and the resulting aggregation of Pt species under high temperatures are responsible for the irreversible deactivation of Pt-Zn/Si-Beta catalyst in PDH reaction.

Propane dehydrogenation catalyzed by in-situ partially reduced zinc cations confined in zeolites

Propane dehydrogenation(PDH), employing Pt-or Cr-based catalysts, represents an emerging industrial route for propylene production. Due to the scarcity of platinum and the toxicity of chromium, alternative PDH catalysts are being pursued. Herein, we report the construction of Zn-containing zeolite catalysts,namely Zn@S-1, for PDH reaction. Well-isolated zinc cations are successfully trapped and stabilized by the Si-OH groups in S-1 zeolites via in-situ hydrothermal synthesis. The as-prepared Zn@S-1 catalysts exhibit good dehydrogenation activity, high propylene selectivity, and regeneration capability in PDH reaction under employed conditions. The in-situ partial reduction of zinc species is observed and the partially reduced zinc cations are definitely identified as the active sites for PDH reaction.

Metal-seed assistant photodeposition of platinum over Ta_(3)N_(5) photocatalyst for promoted solar hydrogen production under visible light

Cocatalysts play a vital role in accelerating the reaction kinetics and improving the charge separation of photocatalysts for solar hydrogen production.The promotion of the photocatalytic activity largely relies on the loading approach of the cocatalysts.Herein,we introduce a metal-seed assistant photodeposition approach to load the hydrogen evolution cocatalyst of platinum onto the surface of Ta_(3)N_(5) photocatalyst,which exhibits about 3.6 times of higher photocatalytic proton reduction activity with respect to the corresponding impregnation or photodeposition loading.Based on our characterizations,the increscent contact area of the cocatalyst/semiconductor interface with metal-seed assistant photodeposition method is proposed to be responsible for the promoted charge separation as well as enhanced photocatalytic H2 evolution activity.It is interesting to note that this innovative deposition strategy can be easily extended to loading of platinum cocatalyst with other noble or non-noble metal seeds for promoted activities,demonstrating its good generality.Our work may provide an alternative way of depositing cocatalyst for better photocatalytic performances.

Application of ammonia probe-assisted solid-state NMR technique in zeolites and catalysis

Solid-state NMR(ssNMR)spectroscopy is a powerful technique for characterizing the surface sites of solid acids and organic intermediates formed during the acid catalyzed reaction.As a very useful probe molecule,ammonia is often utilized to determine the density of solidacids’surface sites by ssNMR spectroscopy.The present mini-review summarizes some of the latest research developments on the quantitative characterization of the acid sites and carbenium ions during the zeolite catalytic reaction by ammonia probe-assisted ssNMR spectroscopy.

Zeolites for separation:Fundamental and application

Material based emerging separation techniques are attracting more and more attention as alternatives to the traditional ones such as distillation and extraction,aiming to reduce energy consumption and pollutant emissions.Due to their structure characteristics,zeolites can act as versatile sieves and adsorbents for molecules and have been successfully applied in some very important separation processes.Herein,two major catalogues of zeolite separations,namely membrane separation and adsorptive separation,are discussed and their underlying mechanisms are focused.In the part of membrane separation,the synthesis strategies toward zeolite membranes are introduced and the uniformly-oriented zeolite membranes are emphasized.In the part of the adsorptive separation,the industrial and popular adsorptive separations with the corresponding zeolite adsorbents are summarized.Generally,membrane separation relies on the molecular diffusion behavior within zeolites while adsorptive separation relies on the guest–host interaction in principle.The key challenges and misconceptions in zeolite separations are highlighted throughout the article.

Cascade adsorptive separation of light hydrocarbons by commercial zeolites

Adsorptive separation of light hydrocarbons by porous solids provides an energy-efficient alternative to state-of-the-art cryogenic distillation.However,an optimal balance between the cost,performance and stability of the sorbent material is yet to be achieved for industrial applications.Here,we report the efficient separation of C2 and C3 hydrocarbons by a faujasite zeolite(Na-X,Si/Al=1.23).A tandem configuration of two fixed-beds packed with Na-X affords complete dynamic separation of the ternary mixture of C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)(1/49.5/49.5;v/v/v)under ambient conditions.Pressure-swing desorption on the latter fixed-bed gives ethylene(>99.50%,1.80 mmol g^(-1))and ethane(>99.99%,1.41 mmol g^(-1)).In situ synchrotron X-ray powder diffraction revealed the binding sites for C_(2)H_(2)and C_(2)H_(4)in Na-X.This study highlights the potential application of commercial zeolites for challenging industrial separations.

铂负载二氧化钛光催化剂在单波长下苯乙炔高选择性加氢（英文）

苯乙烯是一种非常重要的化工原料,它是工业上生产聚苯乙烯、树脂和丁苯橡胶的重要单体,而苯乙烯单体中经常含有苯乙炔杂质,影响苯乙烯的聚合性能,因此研究苯乙炔选择性加氢生成苯乙烯具有十分重要的工业意义.传统的热催化苯乙炔加氢反应会用到易燃易爆的氢气,引起操作的危险性,因此,开发具有环境友好型的加氢反应体系具有很重要的意义.光催化加氢反应利用光生电子强的还原能力,还原质子产生活性的氢物种加氢,相较于传统的热催化使用氢气作为加氢源加氢,能够在温和的条件下实现高选择性加氢.基于此,本文利用Pt/TiO2作为光催化剂,甲醇作为加氢源实现了在385 nm单波长光照下苯乙炔的高选择性加氢.首先,我们利用光沉积的方法将Pt负载在TiO2的表面,通过透射电子显微镜图像和紫外可见吸收光谱表征了负载在TiO2表面Pt的颗粒分布和光学性质.结果表明负载的Pt的颗粒大约在5 nm左右,Pt的负载改变了TiO2在可见光区的吸收性能.XPS结果显示,通过光沉积得到的Pt的价态为金属态和氧化态共存.光催化苯乙炔加氢实验表明,Pt/TiO2催化剂在室温常压条件下不仅具有高的苯乙炔光催化转化率,当光照达8 h后,苯乙炔完全转化,而且在6 h之内苯乙烯选择性保持在91.3%,具有高的苯乙烯选择性.通过对负载的Pt的含量进行了优化,筛选出当Pt的负载量为1 wt%时,苯乙炔的转化率最高.为了对比,利用传统热催化的方法氢气作为加氢源进行了苯乙炔加氢实验,结果发现,使用氢气作为加氢源时,虽然苯乙炔的转化率为100%,但产物是过加氢的产物乙苯.这主要是因为在光催化反应过程中,TiO2导带上的电子迁移至Pt颗粒上,导致Pt的电子密度增加,Pt颗粒表面高的电子密度有利于加氢中间产物苯乙烯的脱附,因此,在光催化加氢过程中不会发生过加氢反应,具有高的苯乙烯选择性.同时,扩展实验表明,Pt/TiO2光催化剂对其他类型的炔烃加氢也具有高的选择性,表明Pt/TiO2光催化炔烃加氢具有普适性.由此可见,光催化炔烃加氢未来将成为一种环境友好而高效的方法.

Efficient Heterogeneous Hydroformylation over Zeolite-Encaged Isolated Rhodium Ions

Alkene hydroformylation is an extremely important industry process currently accomplished via homogeneous catalysis.Heterogeneous hydroformylation is being avidly pursued as a more economical and sustainable process.Herein,we report the construction of zeolite-encaged rhodium catalyst for efficient hydroformylation.Through a facile in situ hydrothermal strategy,isolated Rh^(δ+)(δ=2.5)can be encaged in faujasite and efficiently stabilized via interaction with framework oxygen atoms,producing a Rh@Y model catalyst with well-defined rhodium sites and coordination environment.Rh@Y exhibits high catalytic activity,perfect chemoselectivity,and recyclability in 1-hexene hydroformylation under mild reaction conditions,making it a robust heterogeneous catalyst for potential applications.A state-of-the-art turnover frequency value of 6567 molC=C/molRh/h for Rh@Y can be achieved in 1-hexene hydroformylation at 393 K,outperforming all heterogeneous catalysts and most homogeneous catalysts under comparable conditions.With the well-defined structure of Rh@Y,the detailed mechanism of alkene hydroformylation can be interpreted via theoretical calculations,and the advantages of heterogeneous hydroformylation are well explained.This work provides a promising solution toward efficient heterogeneous noble metal catalysis by encaging stable isolated ions in a zeolite matrix.

Homogeneous-like Alkyne Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation,which is currently accomplished by modified palladium catalysts.Herein,we report that coordinatively unsaturated Ni(II)sites confined in faujasite zeolite,that is,Ni@Y,can efficiently catalyze the selective hydrogenation of various alkynes in both gas-and liquid phase.Spectroscopic and kinetic analyses explicitly reveal that alkyne hydrogenation over Ni@Y follows the homogeneous associative mechanism instead of the classic heterogeneous Horiuti–Polanyi mechanism.Density functional theory calculations confirm that the preferential adsorption of alkynes on coordinatively unsaturated Ni(II)sites is crucial to initiate dihydrogen activation for the subsequent hydrogenation.Ni@Y represents a true heterogeneous catalyst acting as a homogeneous catalyst and shares the advantages of both heterogeneous and homogeneous catalysis.These findings may shed light on the rational design of robust catalysts and new catalytic routes by linking heterogeneous and homogeneous catalysis.

Multifunctional heteroatom zeolites:construction and applications

Multifunctional heteroatom zeolites have drawn broad attentions due to the possible synergistic effects in the catalytic reactions.Remarkable achievements have been made on the synthesis,characterization and catalytic applications of multifunctional heteroatom zeolite,while a review on this important topic is still missing.Herein,current research status of multifunctional heteroatom zeolites is briefly summarized,aiming to boost further researches.First,the synthesis strategies toward heteroatom zeolites are introduced,including the direct synthesis and postsynthesis routes;then,the spectroscopic techniques to identify the existing states of heteroatom sites and the corresponding physiochemical properties are shown and compared;finally,the catalytic applications of multifunctional heteroatom zeolites in various chemical reactions,especially in one-step tandem reactions,are discussed.

Progressive steps and catalytic cycles in methanol-to-hydrocarbons reaction over acidic zeolites

Understanding the complete reaction network and mechanism of methanol to-hydrocarbons remains a key chal-lenge in the field of zeolite catalysis and C1 chemistry.Inspired by the identification of the reactive surface methoxy species on solid acids,several direct mechanisms associated with the formation of the first C-C bond in methanol conversion have been recently disclosed.Identifying the stepwise involvement of the initial intermedi-ates containing the first CC bond in the whole reaction process of methanol to-hydrocarbons conversion becomes possible and attractive for the further development of this important reaction.Herein,several initial unsaturated aldehydes/ketones containing the C-C bond are identified via complementary spectroscopic techniques.With the combination of kinetic and spectroscopic analyses,a complete roadmap of the zeolite catalyzed methanol-to-hydrocarbons conversion from the initial CC bonds to the hydrocarbon pool species via the oxygen-containing unsaturated intermediates is clearly ilustrated.With the participation of both Bronsted and Lewis acid sites in H-ZSM-5 zeolite,an initial aldol-cycle is proposed,which can be closely connected to the well-known dual-cycle mechanism in the methanol-to-hydrocarbons conversion.

High activity of hot electrons from bulk 3D graphene materials for efficient photocatalytic hydrogen production

为经由切开的水的氢生产的有效光催化剂的设计和合成从理论、实际的观点是很重要的。许多基于金属的半导体在最近的十年为这个目的被探索了。这里，第一次完全基于碳的材料，体积三在尺寸上的 cross-linked graphene (3DG ) ，为氢作为光催化剂被开发了生产。它展出 270 摩尔的显著的氢生产率 ??? 琠? 敧敮慲整挠瑹瑯硯捩稠湩 ? 潩獮愠摮爠慥瑣癩? 硯杹湥猠数楣獥 ? 佒 ? 。

Reversed configuration of photocatalyst to exhibit improved properties of basic processes compared to conventional one

Performances of semiconductor photocatalysts are integrally determined by efficiencies of basic processes such as light absorption,charge separation and surface catalysis,but conventional configurations of photocatalysts normally suffers from the competition of light absorption originating from cocatalyst deposition and limited interface charge separation between the photocatalyst and cocatalyst.Herein we give the first proof-of-concept illustration that a reversed configuration of photocatalysts with a core/shell structure of microsized Mo2N cocatalysts and nanosized CdS photocatalysts,which exhibits superior solar hydrogen production to the conventional configuration with nanosized Mo2N cocatalysts deposited on the surface of CdS photocatalysts.It is revealed that the reversed configuration outperforms the conventional one in all areas of light absorption,charge separation and surface catalysis.Strikingly,the special core/shell structure introduced here can well avoid the competition of light absorption by cocatalysts and make an effective confinement effect to promote the surface catalysis of Mo2N.Our finding provides an alternative strategy to improve performances of photocatalysts.