A concise review on surface and structural modification of porous zeolite scaffold for enhanced hydrogen storage

Investigating zeolites as hydrogen storage scaffolds is imperative due to their porous nature and favorable physicochemical properties.Nevertheless,the storage capacity of the unmodified zeolites has been rather unsatisfactory(0.224%-1.082%(mass))compared to its modified counterpart.Thus,the contemporary focus on enhancing hydrogen storage capacities has led to significant attention towards the utilization of modified zeolites,with studies exploring surface modifications through physical and chemical treatments,as well as the integration of various active metals.The enhanced hydrogen storage properties of zeolites are attributed to the presence of aluminosilicates from alkaline and alkaline-earth metals,resulting in increased storage capacity through interactions with the charge density of these aluminosilicates.Therefore,there is a great demand to critically review their role such as well-defined topology,pore structure,good thermal stability,and tunable hydrophilicity in enhanced hydrogen storage.This article aimed to critically review the recent research findings based on modified zeolite performance for enhanced hydrogen storage.Some of the factors affecting the hydrogen storage capacities of zeolites that can affect the rate of reaction and the stability of the adsorbent,like pressure,structure,and morphology were studied,and examined.Then,future perspectives,recommendations,and directions for modified zeolites were discussed.

Synthesis of spherical nano-ZSM-5 zeolite with intergranular mesoporous for alkylation of ethylbenzene with ethanol to produce m-diethylbenzene

Catalytic synthesis of m-diethylbenzene(m-DEB)through alkylation of ethylbenzene(EB)may be a promising alternative route in comparison with traditional rectification of mixed DEB,for which the top priority is to develop efficient and stable heterogeneous catalysts.Here,the spherical nano-ZSM-5 zeolite with abundant intergranular mesoporous is synthesized by the seed-mediated growth method for alkylation of EB with ethanol to produce m-DEB.The results show that the spherical nano-ZSM-5 zeolite exhibits better stability and higher alkylation activity at a lower temperature than those of commercial micropore ZSM-5.And then,the spherical nano-ZSM-5 is further modified by La_(2)O_(3) through acid treatment followed by immersion method.The acid treatment causes nano-ZSM-5 to exhibit the increased pore size but decreased the acid sites,and subsequent La_(2)O_(3) loading reintroduces the weak acid sites.As a result,the HNO_(3)-La_(2)O_(3)-modified catalyst exhibits a slight increase in EB conversion and DEB yield in comparison with unmodified one,and meanwhile,it still maintains high m-DEB selectivity.The catalyst after acid treatment achieves higher catalytic stability besides maintaining the high alkylation activity of EB with ethanol.The present study on the spherical nano-HZSM-5 zeolite and its modification catalyst with excellent alkylation ability provides new insights into the production of mDEB.

Removal of Organochlorine from Model Oil Using Mg-Modified ZSM-5 Zeolite:Dechlorination Performance,Regeneration,and Thermodynamics

Various metal-modified ZSM-5 zeolite adsorbents prepared by the impregnation method were applied to the removal of organic chlorides from model naphtha.The adsorption performance and regeneration stability were investigated by static adsorption experiments.The morphologies,structural features,and physicochemical properties of the adsorbents were characterized by X-ray diffraction,Brunauer-Emmett-Teller analysis,NH3 temperature-programmed desorption,scanning electron microscopy,transmission electron microscopy,and pyridine adsorption infrared spectroscopy.The Mg/ZSM-5 zeolite adsorbent possessed a relatively high specific surface area and good metal dispersion and exhibited the best dechlorination and regeneration performance.The characterization results revealed that introduction of the metal exerted a significant influence on the acidic properties of the catalyst surface.A decrease in the ratio of Brønsted acidic sites to Lewis acidic sites and an increase in the amount of moderately acidic sites were confirmed to be responsible for the excellent adsorption performance of the Mg-modified ZSM-5 zeolite.Furthermore,the Langmuir adsorption isotherm model was applied to study the adsorption equilibrium and thermodynamics of the Mg/ZSM-5 adsorbent under mild conditions.The results revealed that the removal of 1,2-dichloroethane by the Mg/ZSM-5 adsorbent was endothermic,spontaneous,disordered,and primarily involved physical adsorption.

Y Zeolites Modified by Organosilane for Toluene Adsorption under High Humidity Condition

Y zeolites have moderate microporous pore size, large specific surface area, and good hydrothermal stability, which were widely used in industrial adsorption of volatile organic compounds (VOCs), but the performance of Y zeolites in adsorption of VOCs under high humidity conditions is terrible. In this paper, Y zeolites with different silica-alumina ratios were hydrophobically modified by organosilane and characterized by XRD, FTIR, SEM, BET, NMR. In the experiments of static and dynamic adsorption of VOCs by modified Y zeolites, it can be concluded that the static water adsorption capacity of Y zeolites with silica-aluminum ratio of 5 and 40 after silica modification decreased by 62 wt% and 53 wt%, under the conditions of high humidity, GHSV = 15,000 h-1, T = 35°C and initial concentration of toluene C0 = 5000 mg·m-3. The saturation adsorption capacity of toluene was increased from 0.06 g·g-1, 0.09 g·g-1 to 0.15 g·g-1, 0.21 g·g-1, the adsorption selectivity of Y zeolites for water was reduced and that for toluene was increased after Vapor phase silanization overlay modification. The present modification method might carry out targeted modification of zeolites surface, provide research ideas and guidance under high humidity conditions.

The Effect of Hydrophobic Modification of Zeolites on CO2 Absorption Enhancement

Two methods of the modification of zeolite were employed： framework element modification and surface coating, and the influence of the zeolites before and after modification on the CO2 absorption was investigated. It was found that although hydrophobicity of zeolite could be obtained by means of the surficial organic coating in the method of surface coating _mod!fication, partial channel of zeolite would be plugged, as a result, leading to the surface area reducing greatly. Distinctively, the framework element modification method could maintain not only complete lattice structure and adsorption capability of zeolite, but would also obtain a good hydrophobic property. Consequently, significant enhancement on gas absorption by this modified zeolite was achieved and up to a maximum enhancement factor of 2.62. This shows that the solid particles with good enhancement role to gas absorption need not only good adsorptive capability but also certain hydrophobicity. An unsteady heterogeneous model was employed to predict enhancement factor and the calculated results agree well with the experimental data.

Study on Modification of Ultra-Stable Zeolite Prepared by Hydrothermal Method

The ultra-stable zeolite DASY-0.0 was prepared by hydrothermal method in commercial scale. Its structure was further modified via the treatment for cleaning of pores （CP）. The zeolite samples before and after CP treating were analyzed and characterized by XRF, XRD, NMR, IR, BET and DTA. The results showed that, in comparison with the conventional ultra-stable zeolite DASY-0.0 prepared by the hydrothermal process, the CP-modified zeolite SOY0 exhibited a higher relative crystallinity, a larger surface area and pore volume, a higher thermal stability and contained less amorohous non-framework A1.

Characterization and Modification of Indonesian Natural Zeolite for Hydrocracking of Waste Lubricant Oil into Liquid Fuel Fraction

Modification and characterization of natural zeolite under some various methods for hydrocracking catalyst of waste lubricant to gasoline and diesel fractions have been conducted. Natural zeolite from Klaten was activated using hydrothermal treatment at temperature 500 ℃ for 6 h （produced ZAAHd）, the ZA sample was treated with hydrothermal followed by Microwave （produced ZAAHdM）, the ZA sample was treated with HCI 3 N at temperature of 90 ℃ for 30 min （produced ZAAH）, the ZAAH sample was heated in to microwave （produced ZAAHM）, the ZAAHM was treated hydrothermal （produced ZAAHMHd）, the ZAAHMHd sample was heated in to microwave （produced ZAAHMHdM）, soaking of natural zeolit activated by HCl-microwave-hydrothermal-microwave in NH4NO3 1 N which was stirred using stirer at room temperature for 24 h （produced ZAAHMHdMN） and the ZAAHMHdMN sample was heated into microwave （ZAAHMHdMNM）. The heating process by microwave was conducted at 550 watt for 15 rain. Catalyst characterization involved determination of the number of total acid sites using gravimetric method with vapour adsorption of NH3 and pyridine, catalyst crystallinity by XRD （X-ray diffraction） and TO4 （T= Si and AI） site by infra red spectrophotometer （IR）. Hydrocracking of waste lubricants oil was performed in a fixed bed reactor of stainless steel at temperature of 450 ℃, H2 flow rate of 15 mL/min., feed/catalyst ratio of 5. Liquid products of the hydrocracking were analyzed using GC （gas chromatography）. The characterization results showed that various modification of natural zeolite increased acidity and dealumination degree of the catalysts. Products of the hydrocracking were liquid, coke, and gas fractions. Liquid products consisted of gasoline fraction （C5-C12）, diesel fraction （C12-C20）, and heavy oil fraction （〉 C20）.Thc conversion of liquid products was increased with the increase of catalyst acidity. The greatest liquid product conversion was produced by the ZAAHMHdMNM catalyst, i.e., 56.80%, with selectivity towards gasoline, diesel, and heavy oil fractions was 88.37%, 8.61% and 3.02%, respectively. The increase of catalyst acidity increased the selectivity of gasoline fraction.

THE SURFACE MODIFICATION OF ZEOLITE-4A BY CTMAB AND ITS PROPERTIES

The structure and properties of zeolite- 4A modified by hexadecyltrimethyl ammonium bromide (CTMAB) were investigated in this work.Structure char- acterization proved that surface modification onlyinflu- enced the external surface structure and properties of zeo-lite-4A. Properties testing showed that the surface mdi- fication inproved the dispersity of zeolite-4A n lower polar and non-polarsolvents and the adsorbability dyestuff of zeolite-4A in aqueoussolution.

Alkylation of toluene with tert-butyl alcohol over HPW-modified Hβ zeolite

An Hβ-supported heteropoly acid （H3PW12O40 （HPW）/Hβ） catalyst was successfully prepared by wetness impregnation, and investigated in the alkylation of toluene with tert-butyl alcohol for the synthesis of 4-tert-butyltoluene （PTBT）. X-ray diffraction, scanning electron microscopy, transmis- sion electron microscopy, fourier-transform infrared spectroscopy, inductively coupled plas- ma-optical emission spectrometry, the brunauer emmett teller （BET） method, tempera- ture-programmed NH3 desorption, and pyridine adsorption infrared spectroscopy were used to characterize the catalyst. The results showed that loading HPW on Hβ effectively increased the B acidity and decreased the pore size of Hβ. The B acidity of HPW/Hβ was 142.97 μmol/g, which is 69.74% higher than that of Hβ （84.23 μmol/g）. The catalytic activity of the HPW/Hβ catalyst was much better than that of the parent Hβ zeolite because of its high B acidity. The toluene conversion over HPW/Hβ reached 73.1%, which is much higher than that achieved with Hβ （54.0%）. When HPW was loaded on Hβ, the BET surface area of Hβ decreased from 492.5 to 379.6 m2/g, accompa- nied by a significant decrease in the pore size from 3.90 to 3.17 nm. Shape selectivity can therefore play an important role and increase the product selectivity of the HPW/Hβ catalyst compared with that of the parent Hβ. PTBT （kinetic diameter 0.58 nm） can easily diffuse through the narrowed pores of HPW/Hβ, but 3-tert-butyltoluene （kinetic diameter 0.65 nm） diffusion is restricted because of steric hindrance in these narrow pores. This results in high PTBT selectivity over HPW/Hβ （around 81%）. The HPW/Hβ catalyst gave a stable catalytic performance in reusability tests.

Genome-wide profiling of histone H3 lysine 27 trimethylation and its modification in response to chilling stress in grapevine leaves

Histone H3 lysine 27 trimethylation(H3K27me3) is a histone modification associated with transcriptional repression. However, insights into the genome-wide pattern of H3K27me3 in grapevines are limited. Here, anti-H3K27 chromatin immunoprecipitation(ChIP), high-throughput sequencing, and transcriptome analysis were performed using leaves of Vitis amurensis. The leaves were treated at 4°C for 2 h and 24 h and used to investigate changes in H3K27me3 under chilling treatment. The results show that H3K27me3 is well-distributed both in gene regions(-50%) and in the intergenic region(-50%) in the grapevine genome(Vitis vinifera ‘Pinot Noir PN40024'). H3K27me3 was found to be localized in8 368 annotated gene regions in all detected samples(leaves at normal temperature and under chilling treatments) and mainly enriched in gene bodies with the adjacent promoter and downstream areas. The short-term chilling treatments(4°C for 2 h) induced 2 793 gains and 305losses in H3K27me3 modification. Subsequently, 97.3% of the alterations were restored to original levels after 24 h treatment. The ChIP-qPCR for five differential peaks showed similar results to the data for ChIP-seq, indicating that the chilling-induced H3K27me3 modification is reliable.Integrative analysis of transcriptome and ChIP-seq results showed that the expression of H3K27me3 target genes was significantly lower than those of non-target genes, indicating transcriptional repression of H3K27me3 in grapevine leaves. Furthermore, histone methylation alterations were detected in 82 genes and were related to either repression or activation of their expression during chilling stress. The findings provide the genome-wide H3K27me3 patterns in grapevines and shed light on uncovering its regulation in chilling stress responses.

Removal of Nitrophenols by Adsorption Using β-Cyclodextrin Modified Zeolites

Removal of nitrophenols （NPs） from aqueous solutions through the adsorption process by using cationic β-cyclodextrin （CCD） modified zeolite （CCDMZ） was investigated. The effects of particle size, contact time, solution pH values and sodium chloride content in the aqueous on adsorption capacity were evaluated through a series of batch experiments. The results showed that CCDMZ had a higher adsorption capacity for removing NPs at a size fraction of 0.45-0.9 mm while adsorption of NPs on CCDMZ reached equilibrium within 60 min. The adsorption process was apparently influenced by pH values and sodium chloride content in aqueous solution. To ascertain the mechanisms of sorption, the experimental data were modeled by using the pseudo-first and pseudo-second order kinetic equations, and the results indicated that the adsorption kinetics of NPs on CCDMZ well-matched with the pseudo-second order rate expression.

Ceria-modified hierarchical Hβ zeolite as a robust solid acid catalyst for alkenylation of p-xylene with phenylacetylene

A ceria‐modified hierarchical Hβzeolite was prepared by a desilication‐dealumination procedure followed by ceria modification.The catalytic performance of the ceria‐modified and unmodified hierarchical Hβzeolite catalysts for alkenylation of p‐xylene with phenylacetylene was investigated.Various characterization techniques,including X‐ray diffraction,X‐ray fluorescence,nitrogen adsorption‐desorption,and NH3temperature‐programmed desorption,were used to examine the structure‐performance relationships.Our results show that the optimized ceria‐modified hierarchical Hβzeolite catalyst demonstrated higher catalytic activity,selectivity,and stability for alkenylation of p‐xylene with phenylacetylene than those of pristine Hβzeolite.This performance was attributed to more acidic sites and improved accessibility to active sites through larger pores,together with a higher mesoporous surface area and volume resulting from the hierarchical pore architecture and ceria modification.Thus,our5wt%CeO2‐Hβ‐B0.2A0.2catalyst shows great potential for producing alkenyl aromatics through solid acid catalyzed alkenylation.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved

Synthesis of Modified β-Zeolite Under Microwave Irradiation and Its Use on Etherification

zeolite was synthesized by using tetraethyl ammonium hydroxide as the template reagent andmicrowave radiation as the heat source. The effect of the sol composition and the radiation temperature onzeolite crystallinity was investigated. The zeolite was tested and compared with the commercial product, whichwas produced by conventional hydrothermal synthesis method. The physico-chemical properties of the syn-thesized samples, the specific surface area of the samples synthesized under microwave irradiation and porevolume measured by X-ray diffraction apparatus, were better than the conventional samples. The etherificationexperiment on FCC light naphtha in the presence of transition metals modified Hβ-zeolite, which was synthe-sized firstly under microwave irradiation, was studied in a fixed-bed reactor. The effect of catalyst preparationconditions on its activity, stability and the effect of reaction temperature, methanol/tertiary-carbon olefin molarratio and liquid hourly space velocity on the etherification reaction were discussed. The experimental resultsshowed that the different metals modified Hβ-zeolite had different etherification performances. And theconversion of tertiary carbon-olefins of the molybdenum modified Hβzeolite, which was loaded at a concen-tration of 3 percents, was higher than that on 6.0 percent of Hβzeolite. The modified Hβzeolite catalystspossessed favorable prospects for its higher stability.

Synthesis and characterization of an unusual snowflake-shaped ZSM-5 zeolite with high catalytic performance in the methanol to olefin reaction

The ZSM-5 zeolite with an unusual snowflake-shaped morphology was hydrothermally synthesized for the first time,and compared with common ellipsoidal and boat-like shaped samples.These samples were characterized by N2 adsorption-desorption,X-ray fluorescence spectroscopy,scanning electron microscopy,X-ray diffraction,magic angle spinning nuclear magnetic resonance,temperature-programmed desorption of ammonia,and infrared spectroscopy of pyridine adsorption.The results suggest that the BET surface area and SiO2/Al2O3 ratio of these samples are similar,while the snowflake-shaped ZSM-5 zeolite possesses more of the（101） face,and distortion,dislocation,and asymmetry in the framework,resulting in a larger number of acid sites than the conventional samples.Catalysts for the methanol to olefin（MTO） reaction were prepared by loading Ca on the samples.The snowflake-shaped Ca/ZSM-5 zeolite exhibited excellent selectivity for total light olefin（72%） and propene（39%） in MTO.The catalytic performance influenced by the morphology can be mainly attributed to the snowflake-shaped ZSM-5 zeolite possessing distortion,dislocation,and asymmetry in the framework,and lower diffusion limitation than the conventional samples.

Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane

The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature （excluding 800 ℃）. The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature. The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5 zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking.

External surface modification of as-made ZSM-5 and their catalytic performance in the methanol to propylene reaction

Post-synthetic treatment of high-silica as-made ZSM-5 with organic template in the micropores was explored to reduce/remove the external surface acid density of ZSM-5. It is found that Na_2H_2 EDTA treatment can selectively remove the surface Al atoms, but generates new acid sites（likely silanol nests） on the external surface. H_3PO_4 treatment is unable to remove surface Al atoms, while small amount of P is left on the external surface, which effectively decreases the acid density. The catalytic performance of the resultant materials is evaluated in the methanol conversion reaction. H_3PO_4 treatment can effectively improve both the catalytic lifetime and the stability of propene selectivity.This occurs due to a combination of the increased tolerance to the external coke deposition and the depressed coking rate（reduced side reactions）. Na_2H_2 EDTA treatment only prolongs the catalytic lifetime, resulting from the improved tolerance to the external coke deposition. Under the optimized H_3PO_4 treatment condition, the resultant ZSM-5 gives a catalytic lifetime of about 1.5 times longer than the precursor. Moreover, the propene selectivity is improved, showing a slight increasing trend until the deactivation.

The Effect of Coupling Agents on Natural Zeolite-Filled Natural Rubber

Natural zeolite particles of 40, 80 and I00 phr were incorporated into natural rubber （NR） using a two-roll mill. The surface treatment of zeolite particles was expected to improve their cure characteristics and their tensile properties. Two types of silane coupling agents, i.e., bis-[3-（triethoxysilyl）-propyl]-tetrasulfide （Coupling 89） and 3-Octanoylthio-l-propyltriethoxysilane （NXT） at various loadings of 2, 4 and 8 percent by weight （%wt） were selected. The viscosity and cure time of the rubber compound increased, while the scorch time decreased after the treatment of zeolite by both coupling agents. The viscosity of the rubber compound predominantly increased when increasing Coupling 89, however, NXT loadings showed no significant effect on the cure characteristics Moreover, the amount and type of coupling agent influenced the tensile properties of the vulcanizates, as a result of the increase in tensile strength, and tensile modulus with increasing both coupling agents loading. The tensile properties of the vulcanizates increased at low Coupling 89 concentrations （2-4%wt）, but decreased at high Coupling 89 loading （8%wt）. Since NXT has a less bulky structure and lower viscosity compared with Coupling 89, it thus reacts with the silanol groups on the zeolite surface more readily, resulting in the decrease in filler-filler interaction, leading to better tensile properties.

Catalytic roles of the acid sites in different pore channels of H‐ZSM‐5 zeolite for methanol‐to‐olefins conversion

H‐ZSM‐5 zeolite is a typical catalyst for methanol‐to‐olefins(MTO)conversion.Although the performance of zeolite catalysts for MTO conversion is related to the actual location of acid sites in the zeolite framework,the catalytic roles of the acid sites in different pore channels of the H‐ZSM‐5 zeolite are not well understood.In this study,the MTO reaction network,involving the aromatic cycle,alkene cycle,and aromatization process,and also the diffusion behavior of methanol feedstock and olefin and aromatic products at different acid sites in the straight channel,sinusoidal channel,and intersection cavity of H‐ZSM‐5 zeolite was comparatively investigated using density functional theory calculations and molecular dynamic simulations.The results indicated that the aromatic cycle and aromatization process occurred preferentially at the acid sites in the intersection cavities with a much lower energy barrier than that at the acid sites in the straight and sinusoidal channels.In contrast,the formation of polymethylbenzenes was significantly suppressed at the acid sites in the sinusoidal and straight channels,whereas the alkene cycle can occur at all three types of acid sites with similar energy barriers and probabilities.Consequently,the catalytic performance of H‐ZSM‐5 zeolite for MTO conversion,including activity and product selectivity,can be regulated properly through the purposive alteration of the acid site distribution,viz.,the location of Al in the zeolite framework.This study helps to elucidate the relation between the catalytic performance of different acid sites in the H‐ZSM‐5 zeolite framework for MTO conversion,which should greatly benefit the design of efficient catalyst for methanol conversion.

分子筛限域单位点钴体系催化芳香族化合物C-H键自调节高效氧化

通过芳香族化合物的碳-氢键活化与选择氧化,可以将廉价芳香烃类原料转化为高附加值含氧产品,因此,该反应在基础研究和工业生产中均受到广泛关注.传统的苯乙酮生产工艺存在毒性底物使用、催化剂回收困难、反应条件苛刻以及产物收率低等问题.通过大量的研究探索,科研人员进一步改进其生产工艺,利用环烷酸钴作为均相催化剂,实现了无溶剂条件下分子氧直接选择氧化乙苯生成苯乙酮.相比均相催化,多相催化在催化剂回收和产物分离方面具有优势,更适合工业化生产.因此,开发用于乙苯选择氧化制苯乙酮的高效稳定多相催化体系非常重要,但具有较大挑战.本文采用原位配体保护的水热合成法将钴配合物(钴-二乙烯三胺)封装在Y型分子筛中,并经进一步焙烧去除配体成功制得Co@Y分子筛催化剂.在无溶剂、无添加剂的条件下,单位点Co作为Co@Y分子筛催化剂的活性位点可催化乙苯选择氧化生成苯乙酮.X射线粉末衍射、透射电镜、紫外可见光吸收光谱和固体核磁共振谱等结果表明,该单位点Co(Co^(2+))通过与骨架氧原子作用稳定限域在Y型分子筛中.为明确Co@Y分子筛催化剂中单位点Co在乙苯氧化反应中所起的重要作用,本文还对比了不同后合成方法所制备的Y分子筛(Co/Y,Co-Y)催化剂及工业环烷酸钴催化剂的催化性能.结果表明,在相同反应条件下,Co@Y分子筛催化剂表现出最高的催化性能,也说明在乙苯氧化反应过程中Co@Y分子筛催化剂的单位点Co有别于上述其他催化剂的活性位点.此外,在Co@Y催化剂热过滤实验中未检测出Co物种浸出,表明Co@Y分子筛催化乙苯氧化反应为多相催化过程,并且在多次循环测试后,Co@Y催化剂结构和反应活性均未发生明显变化.这两项实验均表明Co@Y催化剂具有高稳定性.值得注意的是,在乙苯氧化反应过程中观察到自加速现象,为此进行了对比实验(添加苯甲醛或1-苯乙醇的对比实验)和反应动力学分析.结果表明,痕量苯甲醛或1-苯乙醇的加入会显著改变Co@Y催化剂在乙苯氧化反应中的催化行为,痕量苯甲醛的加入可将反应表观活化能从69.7降至53.7 kJ/mol.本文也通过第一性原理密度泛函理论(DFT)计算系统研究了Co@Y分子筛催化剂单位点Co处乙苯选择氧化反应机理及反应过程中自加速现象产生的原因.DFT计算结果结合上述对比实验和反应动力学分析结果表明,加入痕量苯甲醛或者1-苯乙醇后部分乙苯会直接氧化生成苯乙酮,而非通过乙苯→1-苯乙醇→苯乙酮的途径生成苯乙酮.DFT计算结果也阐明反应过程中自加速现象的产生源于单位点Co处活性氧物种(O^(*))的生成.该活性氧物种在乙苯、苯甲醛和1-苯乙醇的氧化途径中均能自发生成,并且该物种类似“引发剂”促使后续更多链式反应的发生,在乙苯氧化反应过程中具有非常重要的作用.综上所述,本文为理解芳香族化合物碳-氢键选择氧化实验现象与催化作用机制提供了有益见解,可为理性设计开发更高效的催化剂提供新思路.