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.

Alkali-metal-modified ZSM-5 zeolites for improvement of catalytic dehydration of lactic acid to acrylic acid

Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.

Hydrolysis of cellobiose catalyzed by zeolites—the role of acidity and micropore structure

The roles of acidity and micropore structure of zeolite were studied in the hydrolysis of the model oligosaccharide of cellulose–cellobiose. HZSM-5, HY, HMOR and Hβ zeolites were selected as model catalysts for the hydrolysis of cellobiose. The effect of acidity of zeolite, including the strength, type and location, on its catalytic activity was investigated. The strong Br？nsted acid sites located in micropores are the active sites for the hydrolysis of cellobiose to glucose. Meanwhile, the catalytic performance of zeolite is also dependent on the micropore size of zeolite.

AN ADSORB MODEL OF ORGANIC ACID ON BASIC ZEOLITE NAX

The adsorb model of formic acid on NaX derived from TPD was discussed. It was showed that the adsorb sites were various exposed framework O2- centers bearing different basic intensity and spatial resistance. The h-peak was attributed to O2- near S-III in supercage and l-peak to O2- near S-II in beta-cage of faujusite zeolite. The model can explain the experimental results. Meanwhile, a relative standard of basic intensity based on TPD of formic acid was founded.

Acidity Evaluation of Industrially Dealuminated Y Zeolite via Methylcyclohexane Transformation

The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).

THE EFFECT OF ACID TREATMENT ON THE STABILITY OF POLYMORPHS IN BETA ZEOLITE

The stability of beta zeollie in acid solution and the effect of acid treatment on the polymorphs in beta zeolite were studied. This zeolite is easily dealuminated by HCI treatment but its framework highly resistent to acidity.In β zeolite, polymorph A is less stable than polymorph B.The chirality of β zeolite can be modified by the method of acid treatment.

Synthesis of ZSM-5 with the silica source from industrial hexafluorosilicic acid as transalkylation catalyst

A new effective process to improve the utilization of industrial fluorosilicic acid of phosphate fertilizer by-product has been investigated to comprehensive application of the silicon and fluorine source. Two-step ammoniation was applied to recover high-quality silica. The recovered silica can be used to hydrothermal synthesize ZSM-5 zeolite without impurity phase contamination, which was confirmed by XRD, TG, SEM, BET and EDS characteristic techniques. It was found that with the increase of SiO_2/Al_2O_3 ratio and the extension of reaction time, the crystal type transform from the orthorhombic to the monoclinic phase. The impurity fluorine content of the recovered SiO_2 from H_2SiF_6 has great influence on the hydrothermal process for ZSM-5 crystal structure formation.Moreover, the increase of fluorine ions content in the hydrothermal process can control the crystal morphology and size of synthesized ZSM-5. Catalytic properties of synthesized HZSM-5 with different SiO_2/Al_2O_3 ratio in transalkylation of toluene and 1,2,4-trimethylbenzene show good and stable catalytic performance. The ZSM-5 synthesized with recovered silica source exhibits similar catalyst life as the performance of small particle size HZSM-5, because the ZSM-5 synthesized with the silica source from industrial hexafluorosilicic acid prefers a thin disk crystal along the b axis direction, which shortens the diffusion distance of generated products.

Zeolitic germanosilicate analogue to pharmacosiderite crystallized in an acidic medium

Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.

Production of jet fuel intermediates from biomass platform compounds via aldol condensation reaction over iron-modified MCM-41 lewis acid zeolite

Liquid fuel intermediates could be produced via aldol condensation reaction between furfural or 5-hydroxymethylfurfural(HMF)and acetone.It was found that iron-modified MCM-41 zeolite can be an effective Lewis acid catalyst for C-C bond formation via aldol condensation of furfural or HMF with acetone.The 4-(2-furyl)-3-buten-2-one and 1,5-di-2-furanyl-1,4-pentadien-3-one(FAc and F_(2)Ac),or 1,5-di-2-furanyl-1,4-pentadien-3-one and 1,5-bis[(5-hydroxlmethyl)-2-furanyl]-1,4-pentadien-3-one(HAc and H_(2)Ac),as two main condensation products of furfural with acetone or HMF with acetone,were observed.After 24 h at 160℃,86.9%conversion of furfural with 60.0%yield of the FAc as well as 7.5%yield of the F_(2)Ac and 88.9%conversion of the HMF with 41.1%yield of the HAc as well as 3.5%yield of the H_(2)Ac were achieved.Although furfural or HMF conversion was almost same after 24 h at 160℃,iron-modified MCM-41 zeolite catalyst displayed an enhanced selectivity to condensation products of furfural with acetone.In addition,catalysts showed an improved selectivity to the F_(2)Ac and H_(2)Ac at higher reaction temperature.The reusability and regeneration studies showed that iron-modified MCM-41 zeolite catalyst could not be reused directly,but could be regenerated by calcination in air,and the catalytic perfor-mance of regenerated catalyst was acceptable.

Flexible regulation of C3^=/C2^= ratio in methanol-to-hydrocarbons by delicate control of acidity of ZSM-5 catalyst

Avery wide range of the C3^=/C2^= ratio from 0.72 to 7.56 with high C2^= ＋ C3^= selectivity of around 66%in the methanol-to-hydrocarbons process can be realized over ZSM-5 catalyst in a fixed-bed reactor.We firstly conduct a single factor experiment of acidity,demonstrating that the acidity control of MTH catalyst is crucial to adjusting light olefins selectivity.Weak Bronsted acid sites favor to high C3^= selectivity（59.0%）due to the suppression of the conversion reactions from the alkene-based to arene-based cycle,while Lewis acid sites conduce to high C2^= selectivity（39.6%） due to the promotion of the conversion reactions for the aromatics formation and steric constraints of Lewis acid sites making the aromatics crack more efficiently to C2^=.