A high-surface-area silicoaluminophosphate material rich in Brnsted acid sites as a matrix in catalytic cracking

A transparent gel-like mesoporous silicoaluminophosphate material （SAP） with molar ratio of Si/Al = 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus （P） into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area （up to 492 m2/g） exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Br／＂{o}nsted acidic sites （up to 48.44 μmol/g） and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L （Lewis acid/Br？nsted acid） increased to 1.15. The performances of samples as matrices for the catalytic cracking of heavy VGO were investigated. At 520 ℃, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity （2.86%） than conventional FCC matrices, such as kaolin and amorphous silica-alumina.

HZSM-5沸石中Lewis酸与Brnsted酸协同作用下的甲基环己烷开环反应(英文)

由于水蒸气处理HZSM-5生成的骨架外铝在分子筛中体现Lewis酸性,分子筛中骨架外铝物种的可移动性导致Lewis酸与分子筛本身的Br nsted酸在空间上具有临近性.当甲基环己烷分子在HZSM-5的笼中转化时,Lewis酸与Br nsted酸的协同作用加快了甲基环己烷分子的转化速率,且骨架外铝物种浓度越高,这种协同效应越明显.而产物的选择性只与催化剂的孔道结构有关,与水蒸气处理所导致的酸性质的变化无关.

负载型V_2O_5/TiO_2催化剂表面分散状态和性质对氨选择性催化还原NO性能的影响(英文)

采用多种物理化学手段研究了不同负载量V2O5/TiO2催化剂的VOx物种分散状态、表面酸性、可还原性及其选择性催化还原(SCR)NO性能.结果表明,V2O5在锐钛矿TiO2表面的实测单层分散容量约为1.14mmol V/100m2TiO2,与"嵌入模型"的估算值相符,表明分散态的钒离子应键合在TiO2表面的八面体空位上.随着V2O5负载量的增加,V2O5/TiO2催化剂上NO转化频率(TOF)先急剧增加,至0.70mmol V/100m2TiO2(略超过分散容量的一半)时达到极大(约8.3×10-3s-1),然后又急剧下降;同时,孤立VOx物种可能倾向于分散在相邻的八面体空位上,且通过V-O-V化学键相连形成聚合的VOx物种,V-O-V键所占比例增加而V-O-Ti键所占比例减小,催化剂表面单位钒离子的Brnsted酸中心量增加,故催化剂的TOF急剧增加.随着负载量进一步增加,虽然催化剂表面单位钒离子的Brnsted酸中心量仍缓慢增加,但V-O-Ti键所占比例减少,导致钒离子的可还原性下降,另外,分散容量以上时晶相V2O5的形成也导致钒离子表面利用率下降,从而导致催化剂的TOF下降.桥式Brnsted酸位(V-O(H)-V)也是SCR反应活性中心之一,不同负载量V2O5/TiO2催化剂上SCR活性与表面VOx物种的分散状态、表面酸性和钒离子可还原性密切相关.

负载型硫酸铁对烯烃齐聚催化作用的研究 Ⅲ.Fe_2(SO_4)_3/γ-Al_2O_3的表征

用ＸＲＤ方法对Ｆｅ２（ＳＯ４）３／γ－Ａｌ２Ｏ３催化剂进行了表征，发现在Ｆｅ担载量不大于７ｗ％时，Ｆｅ２（ＳＯ４）３单层分散在γ－Ａｌ２Ｏ３的表面上。ＩＲ检测结果表明，在该催化剂表面上Ｌ酸中心与Ｂ酸中心共存，Ｌ酸量与Ｂ酸量的比例随焙烧温度的升高而增大。

超稳Y分子筛B酸中心可接近性的研究

超稳Y分子筛B酸中心可接近性是影响其催化裂化性能的关键因素,选取超稳Y分子筛(USY)和常规HY分子筛进行对比,结合晶格结构和孔结构表征参数,采用原位红外光谱技术以3种不同尺寸的探针分子(吡啶、2,6-二甲基吡啶、2,6-二叔丁基吡啶)对两种分子筛的酸中心可接近性进行对比,并以大港轻柴油为原料进行催化裂化微反活性评价。结果表明:USY分子筛的超笼内B酸中心对较大尺寸探针的可接近性明显优于常规HY分子筛,并推断较低的B酸密度是USY分子筛表现出更高超笼内B酸中心可接近性的主要原因;USY分子筛微反活性为69%,明显高于常规HY分子筛。

CrOx supported on high-silica HZSM-5 for propane dehydrogenation

Industrial propane dehydrogenation(PDH)catalysts generally suffer from low catalytic stability due to the coke formation onto the catalyst surface to cover the active sites.The exploitation of an efficient catalyst with both high catalytic selectivity and long-term stability toward PDH is of great importance but challenging to make.Herein CrOx supported on high-silica HZSM-5 with a SiO2/Al2O3 ratio of 260(Cr/Z-5(260)is synthesized by a simple wet impregnation method,which exhibits high catalytic activity,good selectivity and excellent stability for PDH.At a weight hourly space velocity(WHSV)of 0.59 h-1,a propylene formation rate of 4.1 mmol g-1cath-1(~32.6% propane conversion and ~94.2% propylene selectivity)can be maintained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,which is much better than commercial Cr/Al2O3(Catofin process,catalyst life is several hours)at the same reaction conditions.With increasing the WHSV to 5.9 h-1,a high propylene formation rate of 27.9 mmol gcat-1h-1can be obtained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,demonstrating a very promising PDH catalyst.Characterization results and Na+doping experiments reveal that the Cr species combined with Br?nsted acid sites in Cr/HZSM-5 catalysts are responsible for the high catalytic performance.In particular,the Br?nsted acid sites in HZSM-5 zeolite could increase the propane adsorption and enhance the C–H bond activation.Furthermore,the high surface area and well-defined pores of HZSM-5 zeolite can provide a special environment for the dispersion and stabilization of Cr species,thus guaranteeing high catalytic activity and stability.

Effects of support acidity on the reaction mechanisms of selective catalytic reduction of NO by CH_(4) in excess oxygen

The reaction mechanisms of selective catalytic reduction(SCR)of nitric oxide(NO)by methane(CH4)over solid superacid-based catalysts were proposed and testified by DRIFTS studies on transient reaction as well as by kinetic models.Catalysts derived from different supports would lead to different reaction pathways,and the acidity of solid superacid played an important role in determining the reaction mechanisms and the catalytic activities.Higher ratios of BrØnsted acid sites to Lewis acid sites would lead to stronger oxidation of methane and then could facilitate the step of methane activation.Strong BrØnsted acid sites would not necessarily lead to better catalytic performance,however,since the active surface NO_(y) species and the corresponding reaction routes were determined by the overall acidity strength of the support.The reaction routes where NO_(2)moiety was engaged as an important intermediate involved moderate oxidation of methane,the rate of which could determine the overall activity.The reaction involving NO moiety was likely to be determined by the step of reduction of NO.Therefore,to enhance the SCR activity of solid superacid catalysts,reactions between appropriate couples of active NO_(y)species and activated hydrocarbon intermediates should be realized by modification of the support acidity.

Regeneration of commercial selective catalyst reduction catalysts deactivated by Pb and other inorganic elements

The regeneration of commercial SCR（Selective Catalyst Reduction） catalysts deactivated by Pb and other elements was studied.The deactivated catalyst samples were prepared by chemical impregnation with mixed solution containing K_2SO_4,Na_2SO_4,CaSO_4,Pb（NO_3）_2and NH_4H_2PO_4.A novel method combining Ethylenediaminetetraacetic acid disodium salt（EDTA-2Na） and H_2SO_4solution（viz.catalysts treated by dilute EDTA-2Na and H_2SO_4 solution in sequence） was used to recover the activity of deactivated samples,and the effect was compared with single H_2SO_4,oxalic acid,acetic acid,EDTA or HNO_3 solutions.The surface structure,acidity and reducibility of samples were characterized by N_2adsorption–desorption,inductively coupled plasma optical emission spectrometer（ICP-OES）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray fluorescence（XRF）,H-2-temperature programmed section（H_2-TPR）,NH3-temperature programmed desorption（NH3-TPD） and in situ DRIFTS.Impurities caused a decrease of specific surface area and surface reducibility,as well as Br？nsted acid sites,and therefore led to severe deactivation of the SCR catalyst.The use of an acid solution alone possibly eliminated the impurities on the deactivated catalyst to some extent,and also increased the specific surface area and Br？nsted acid sites and promoted the surface reducibility,thus recovered the activity partially.The combination of EDTA-2Na and H_2SO_4 could remove most of the impurities and improve the activity significantly.The removal of Pb should be an important factor for regeneration.Due to a high removal rate for Pb and other impurities,the combination of EDTA-2Na and H_2SO_4 solutions provided the best efficiency.

Effect of Ce doping into V_(2)O_(5)-WO_(3)/TiO_(2) catalysts on the selective catalytic reduction of NO_(x) by NH_(3)

In this work, the effectiveness of V2O5-WO3/TiO2 catalysts modified with different CeO2 contents by impregnation and co-precipitation methods on the selective catalytic reduction of NOxby NH3 have been studied comparatively by various experimental techniques. The results showed that the NO conversion of V2O5-WO3/CeO2-TiO2 catalysts modified by co-precipitation method obviously increased with the Ce doping contents in the studied range below 20%（All Ce contents are in mass fractions）, but the NO conversion of V2O5-WO3/CeO2/TiO2 catalysts modified by impregnation methods was lower than V2O5-WO3/CeO2-TiO2 catalysts especially beyond 2.5% Ce doping contents. The V2O5-WO3/CeO2-TiO2 catalysts showed better SCR activity, wider reaction window, and higher sulfur and water resistance. The characterization results elucidated that the modified catalysts by co-precipitation method exhibited higher specific surface area, much better dispersity of Ce component, more Ce^（3＋）species and more Br？nsted acid sites than that by impregnation. The vacancies caused by more Ce^（3＋）species were favorable for more NO oxidation to NO2, and the interaction between Ce species and WOxspecies generated more Br？nsted acid sites. It could be supposed that dispersed Ce Oxspecies and WOxspecies offered more second active centers respectively to adsorb oxygen and activate ammonia as co-catalysis to the primary active center of V ions, thus facilitated the better SCR activity of modified V2O5-WO3/CeO2-TiO2 catalysts by coprecipitation methods. The co-precipitation methods with Ce component were more suitable for production of modified commercial V2O5-WO3/TiO2 catalysts.

Catalytic Hydration of Aromatic Alkynes to Ketones over H-MFI Zeolites

The hydration of alkyne represents the most straightforward and simplest route toward the synthesis of ketone. Herein, Brønsted acidic zeolites are explored as potential catalysts for the liquid-phase phenylacetylene hydration. The topology structure and Si/Al ratio are disclosed to be key factors controlling the catalytic activity of zeolites. Typically, H-MFI zeolite with a Si/Al molar ratio of 13 exhibits the highest catalytic activity, with turnover frequency of 6.0 h-1 at 363 K. Besides, H-MFI zeolite shows good catalytic stability and recyclability in the reaction of phenylacetylene hydration, and the substrate scope can be simply extended to other soluble aromatic alkynes. The reaction mechanism of phenylacetylene hydration is investigated by means of kinetic and spectroscopic analyses. The Markovnikov electrophilic addition of phenylacetylene by hydrated protons is established as the rate-determining step, followed by deprotonation and enol isomerization to derive acetophenone product.