Cu/SSZ-13催化剂脱硝活性中心与催化性能构效关系的研究

NH₃选择性催化还原NO_x（NH₃-SCR）是目前最有应用前景的柴油车尾气净化技术,该技术的核心是开发具备优异催化性能的催化剂。以具有菱沸石（chabazite,CHA）结构的小孔分子筛SSZ-13为载体制备的Cu/SSZ-13催化剂,因具有优异的催化性能和水热稳定性能而受到广泛关注。制备了系列Cu_x/SSZ-13催化剂,并通过CO原位漫反射红外光谱（DRIFT）和H₂-TPR等方法能够确定具有高催化活性的铜离子在SSZ-13分子筛上的落位和存在状态。CO红外吸附实验发现,采用Cu(NO₃)₂水溶液离子交换法制备的Cu/SSZ-13催化剂上存在多种落位的Cu⁺活性中心。在较低的Cu⁺交换度条件下,Cu⁺优先落位于SSZ-13分子筛的八元环位置,随着交换度的提高,Cu⁺开始落位于SSZ-13分子筛双六元环的位置。H₂-TPR结果表明Cu_x/SSZ-13催化剂上也存在大量落位在八元环位置不稳定的Cu²⁺,这些Cu²⁺很容易被还原为Cu⁺。Cu_x/SSZ-13催化剂经800℃水蒸气连续老化16 h,分子筛骨架崩塌程度随着Cu含量的增加而提高,骨架铝的脱除,导致Cu物种发生团聚,而第二金属Ce元素的引入能够在一定程度上提高Cu/SSZ-13的水热稳定性。催化剂构效关系研究表明,具有一定量稳定存在的Cu⁺,并且拥有大量不稳定存在Cu²⁺的催化剂具有较宽温度范围的脱硝性能。     

碱改性ZSM-5分子筛制备与催化加氢脱硫芳构化性能

采用0.2 mol/L的NaOH溶液以及浓度均为0.2 mol/L的NaOH和TPAOH的混合溶液,分别对ZSM-5分子筛进行脱硅处理。利用XRD、N_2吸附-脱附、SEM及NH_3-TPD等方法对处理前后样品进行表征。以脱硅处理后的ZSM-5分子筛为载体,采用等体积浸渍法制备了Co-Mo-P/ZSM-5催化剂,以全馏分FCC汽油为原料,考察了该催化剂的加氢脱硫及芳构化性能。结果表明,单纯强碱NaOH溶液处理对ZSM-5分子筛的晶体结构影响较大,造成分子筛骨架结构坍塌,酸性降低;TPAOH的存在保护ZSM-5分子筛骨架结构,提高ZSM-5分子筛的结晶度,并且在生成介孔的同时,最大限度地保留了原微孔结构,并调变了酸性。碱处理后制得的Co-Mo-P/HZSM-5(C-T)催化剂表现出良好的加氢脱硫与芳构化性能。     

碱改性ZSM-5分子筛制备与催化加氢脱硫芳构化性能

采用0.2 mol/L的NaOH溶液以及浓度均为0.2 mol/L的NaOH和TPAOH的混合溶液,分别对ZSM-5分子筛进行脱硅处理。利用XRD、N_2吸附-脱附、SEM及NH_3-TPD等方法对处理前后样品进行表征。以脱硅处理后的ZSM-5分子筛为载体,采用等体积浸渍法制备了Co-Mo-P/ZSM-5催化剂,以全馏分FCC汽油为原料,考察了该催化剂的加氢脱硫及芳构化性能。结果表明,单纯强碱NaOH溶液处理对ZSM-5分子筛的晶体结构影响较大,造成分子筛骨架结构坍塌,酸性降低;TPAOH的存在保护ZSM-5分子筛骨架结构,提高ZSM-5分子筛的结晶度,并且在生成介孔的同时,最大限度地保留了原微孔结构,并调变了酸性。碱处理后制得的Co-Mo-P/HZSM-5(C-T)催化剂表现出良好的加氢脱硫与芳构化性能。     

稀土元素(Y、Nd、Ce、La)改性NaY分子筛催化乳酸脱水制丙烯酸

采用浸渍法以稀土元素(Y、Nd、Ce、La)对NaY分子筛进行改性,并以改性后的分子筛为催化剂,考察催化乳酸脱水制丙烯酸反应活性。通过NH₃-TPD、CO₂-TPD和XRD等对催化剂进行表征,结果表明,稀土元素进入NaY分子筛骨架,其中,La对分子筛晶体结构影响最小;随着负载稀土元素离子半径的增大(Y³⁺＜Nd³⁺＜Ce³⁺＜La³⁺） ,总酸性位数量减少,除了重稀土元素Y,弱酸性位比例和中等强度碱性位数量增多,La改性最有利于丙烯酸的生成。稀土元素改性的NaY分子筛在一定程度上提高丙烯酸收率,抑制乙醛生成。以质量分数38%的乳酸为原料,在空速3 h^-1、反应温度325 ℃和2%La/NaY分子筛为催化剂时,丙烯酸收率为54.2%,而未改性NaY分子筛上丙烯酸收率仅为34.7%。     

高硅铝比小晶粒NaY分子筛/高岭土复合物的合成及其催化裂化性能

以两种不同粒径的高岭土为原料,采用水热法合成了高硅铝比小晶粒NaY分子筛/高岭土复合物,通过XRD、SEM、晶粒度分析和N₂物理吸附等表征手段对复合物进行了结构和形貌表征。结果表明,与商品NaY相比,高岭土合成样品的结构稳定性和水热稳定性显著提高,以细化高岭土为原料合成样品的晶粒尺寸达310 nm,比表面积达807 m²·g^-1。以改性NaY分子筛/高岭土复合物为活性组分制备了催化裂化催化剂,采用NH₃程序升温脱附(NH₃-TPD)技术对其酸性特征进行了分析,并在小型微反装置上对其重油催化裂化性能进行了评价。研究结果发现,随着骨架硅铝比增大,催化剂表面酸中心强度增加,而酸量下降。采用细化高岭土合成的NaY分子筛/高岭土复合物的分子筛晶粒更小,催化剂酸中心数量以及催化裂化性能均大幅度提升。随着高温焙烧高岭土/偏高岭土质量比的增加,合成产物中的高岭土基质含量增加,催化剂表面酸中心强度下降。以原料高温焙烧高岭土/偏高岭土质量比为0.5,骨架硅铝比为6.1(摩尔比)的样品制备的催化剂,去柴重油转化率高达85.4%,同时有高达64.2%的汽油收率,表现出优异的重油催化裂化性能。     

柠檬酸复合改性对多环芳烃选择性开环铂/Beta催化剂性能的影响

通过水热处理、柠檬酸处理及其复合处理对Beta分子筛进行后改性,并以改性后的载体制得铂/Beta催化剂。采用X射线衍射（XRD）、X射线荧光光谱仪（XRF）、程序升温脱附（NH₃-TPD）、红外吡啶吸附（Py-IR）、骨架铝核磁共振技术（²⁷Al MAS NMR）及骨架硅核磁共振技术（²⁹Si MAS NMR）等表征了改性前后Beta分子筛的物化性质,并考察了改性前后铂/Beta的多环芳烃选择性开环性能。结果表明,Beta分子筛在柠檬酸处理过程中可同时发生络合脱铝与骨架补铝,实现骨架铝的再分布;Beta分子筛在水热处理过程中优先脱除稳定性相对较低的Si（2 Al）处骨架铝,产生骨架缺陷的同时生成一定比例的二次介孔结构;水热-柠檬酸复合处理影响Beta分子筛骨架补铝及骨架铝再分布的效果,水热处理后Beta分子筛中存在更多的骨架缺陷,促进活性Al（OH）₂⁺物种的骨架补铝作用。当Beta分子筛采用水热-柠檬酸复合处理顺序时,骨架补铝及骨架铝再分布效果显著,样品以中强酸为主,且具有较高的B酸量与L酸量的比值,所制备催化剂的多环芳烃选择性开环活性及稳定性最优。     

工业氟硅酸合成钛硅介孔分子筛催化环己烯环氧化

利用磷肥工业副产的氟硅酸为原料,在十六烷基三甲基溴化铵（CTAB）溶液中与氨水和钛酸四丁酯（TBOT）反应,水热陈化制取钛硅介孔分子筛,通过改变水热时间、CTAB的加入量、硅钛比和模板剂的脱除方法研究实验条件对钛硅介孔分子筛的结构和性能的影响,采用氮气吸脱附、扫描电镜、透射电镜和固体紫外漫反射对样品进行表征。结果表明,SiO₂:CTAB:TBOT:NH₃:H₂O的摩尔比为1:1.50:0.03:10:150,水浴时间为5 h时,所得样品的比表面积可达1116 m²·g^-1,介孔体积为0.79 cm³·g^-1。合成的钛硅介孔分子筛作为催化剂应用于环己烯环氧化反应,环己烯的转化率可达68.10%,环氧环己烷产物选择性为96.60%,Ti活性位的转化频率达到99.5 h^-1。该方法可以提高磷肥副产低浓度氟硅酸的附加值,降低钛硅介孔分子筛催化剂的生产成本。     

硼掺杂Y分子筛的合成、改性及烯烃脱除性能研究

采用水热合成法制备了硼掺杂Y分子筛(B-Y分子筛),并对其进行铵交换和水热处理,得到了改性B-Y分子筛(B-USY分子筛)。利用多种表征技术对B-Y分子筛及B-USY分子筛的组成、孔道结构、酸性质进行了表征,并将改性后的B-USY分子筛应用于重整生成油脱烯烃反应。结果表明：引入硼以后,Y分子筛的晶胞参数减小、相对结晶度降低、骨架稳定性下降;硼的引入促使改性过程中脱铝深度增加,并且形成连通介孔。相比于未掺杂硼的Y分子筛改性后的USY分子筛,B-USY分子筛具有丰富的连通介孔和良好的孔道扩散性能,并且保留了更多弱的B酸位点。以重整C₇⁺芳烃为原料,在反应温度为170℃、反应压力为1.2 MPa、空速(LHSV)为10 h^-1条件下,B-USY分子筛催化剂的单程寿命较USY分子筛催化剂提升30%。     

USY分子筛表面酸性的调变及其在催化脱除芳烃中烯烃的应用

详细论述了柠檬酸对USY分子筛的改性作用,以脱除高溴指数芳烃中烯烃的反应为例对其催化活性进行了评价。实验结果表明:0.2mol/L柠檬酸溶液酸性适宜,对分子筛的骨架铝以及非骨架铝进行了有效的脱除,脱除的铝在分子筛中以无定形的非骨架铝形式存在。柠檬酸改性过程可使分子筛的介孔面积以及介孔孔容增大,这十分有利于减缓分子筛的失活速率。柠檬酸改性过程使分子筛表面的强B酸减少,强L酸增多,这有助于减缓分子筛上积炭的生成速率。经过柠檬酸改性的USY分子筛对脱除芳烃中微量烯烃的催化效果明显高于目前工业中在用的普通白土和改性白土。再生实验说明,经3次焙烧再生后,改性分子筛的活性依然在90%以上,具有很好的可再生性。     

后处理法制备多级孔Y型分子筛及其加氢裂化性能研究

以柠檬酸和乙二酸四乙酸二钠(EDTA-2Na)为复合改性剂,通过后处理法制备出具有多级孔结构的Y分子筛。在保证分子筛结晶度的同时,柠檬酸和EDTA-2Na可有效脱除骨架铝和六配位非骨架铝物种。改性后Y分子筛的骨架硅铝摩尔比[n(SiO₂)/n(Al2O₃)]提高1倍,结晶度仅降低1. 3%;分子筛的比表面积得到有效提高,介孔含量明显增加,并且连通性更好。以其作为酸性组分制备的加氢裂化催化剂,馏分油总收率比商业USY分子筛提高6. 5%。     

Selective catalytic reduction of NO on copper-exchanged zeolites: the role of the structure of the zeolite in the nature of copper-active sites

Copper-exchanged zeolites with different structures (CuMFI, CuMOR and CuY) used as catalysts on the selective catalytic reduction (SCR) of NO by propene have been studied. Different types of Cu species were identified (Cu²⁺, Cu⁺, and CuO) by H₂-TPR and NO TPD. The structure of each zeolite determines the nature and concentration of those species and the catalytic behavior for SCR of NO by propene in the presence of oxygen. A correlation was observed between the catalytic activity, and the presence of isolated Cu²⁺ species, which is enhanced by MFI structure.     

Ce修饰Na Y分子筛负载PdO纳米晶催化剂用于苯的催化氧化反应

以CeO_2修饰多孔NaY分子筛作为载体,采用高温液相还原法制备纳米晶PdO催化剂,用于低浓度苯催化氧化反应。采用XRD、N2吸附-脱附、透射电镜-能谱(HRTEM-EDS)、H2程序升温还原(H_2-TPR)、O_2程序升温脱附(O_2-TPD)和程序升温表面反应(TPSR)等对载体和催化剂进行表征。结果表明,NaY分子筛结构稳定,比表面积651 m~2·g~(-1)和孔容0. 326 cm~3·g~(-1),纳米晶PdO能够较均匀地分散在NaY载体上,颗粒尺寸约(3～5) nm。加入一定量CeO_2后,Pd O以较小的纳米晶颗粒形式分散在CeO_2周围,活性组分与助剂协同作用促进了催化剂中晶格氧的流动性,明显改善了0. 2%Pd/NaY的氧化性能。0. 2%Pd/8%Ce/NaY表现出最佳催化活性和良好稳定性,250℃可完全催化降解1000×10~(-6)的苯,并且230℃连续反应100 h,催化剂转化率稳定在86%。     

Phi zeolite synthesized by template-free method for selective catalytic reduction of NO

Nitrogen oxide (NO_x) is one of the major air pollutants. Using a copper-based zeolite with a chabazite structure (CHA) as a catalyst, the selective catalytic reduction (SCR) technology can effectively remove NO_x. This work introduces a low silica CHA type zeolite with structural defects (zeolite Phi, with Si/Al of 4.7). The zeolite Phi is synthesized through a hydrothermal method without adding any template, which is low-cost and environment-friendly. The Cu-exchanged Phi is abundant of surface acidity and isolated Cu²⁺, showing a superior low-temperature activity, a wide work temperature window and a good hydrothermal stability. The presence of Na or Mg decreases the surface acidity and isolated Cu²⁺. The hydrothermally aged Na,Cu/Phi and Mg,Cu/Phi present different levels of framework collapse, which correspondingly induces catalyst deactivation.     

Selective catalytic reduction of NO with propene over CuMFI zeolites: dependence on Si/Al ratio and copper loading

Selective catalytic reduction of nitrogen oxide by propene in an oxidising atmosphere was studied on several CuMFI catalysts with different Si/Al ratios (11 Si/Al 100) and different copper loadings (between 0 and 5.5 wt.-%). From the results it was observed that the influence of zeolite Si/Al ratio on CuMFI catalytic activity for NO SCR by propene is dependent on the catalyst copper loading. Furthermore, the effect of catalyst copper loading on catalytic performance depended on the catalyst Si/Al ratio. The results also demonstrated that CuMFI catalysts with different Si/Al ratios and copper loadings, but with the same Cu/Al ratio and, therefore, the same copper exchange level have similar catalytic activity profiles for NO SCR.

It was further observed that not all Cu cations exchanged into MFI catalysts have equivalent catalytic activity for NO SCR, which made the existence of different copper environments on CuMFI catalysts evident, isolated Cu²⁺ ions being the most active species for NO SCR by propene.

Moreover, the results showed an improvement of the CuMFI catalytic activity at low temperatures by increasing the catalyst copper exchange level and, consequently, decreasing the number of Brönsted acid sites, which can be performed either by increasing the zeolite Si/Al ratio or copper loading.     

Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Mesoporous Y zeolites were prepared by the sequential chemical dealumination (using chelating agents such as ethylenediaminetetraacetic acid, H₄EDTA, and citric acid aqueous solutions) and alkaline desilication (using sodium hydroxide, NaOH, aqueous solutions) treatments. Specifically, the ultrasound-assisted alkaline treatment (i.e., ultrasonic treatment) was proposed as the alternative to conventional alkaline treatments which are performed under hydrothermal conditions. In comparison with the hydrothermal alkaline treatment, the ultrasonic treatment showed the comparatively enhanced efficiency (with the reduced treatment time, i.e., 5 min vs. 30 min, all with 0.2 mol·L⁻¹ NaOH at 65°C) in treating the dealuminated Y zeolites for creating mesoporosity. For example, after the treatment of a dealuminated zeolite Y (using 0.1 mol·L⁻¹ H₄EDTA at 100°C for 6 h), the ultrasonic treatment produced the mesoporous zeolite Y with the specific external surface area (S_external) of 160 m²·g⁻¹ and mesopore volume (V_meso) of 0.22 cm³·g⁻¹, being slightly higher than that by the conventional method (i.e., S_external = 128 m²·g⁻¹ and V_meso = 0.19 cm³·g⁻¹). The acidic property and catalytic activity (in catalytic cracking of n-octane) of mesoporous Y zeolites obtained by the two methods were comparable. The ultrasonic desilication treatment was found to be generic, also being effective to treat the dealuminated Y zeolites by citric acid. Additionally, the first step of chemical dealumination treatment was crucial to enable the effective creation of mesopores in the parent Y zeolite (with a silicon-to-aluminium ratio, Si/Al= 2.6) regardless of the subsequent alkaline desilication treatment (i.e., ultrasonic or hydrothermal). Therefore, appropriate selection of the condition of the chemical dealumination treatment based on the property of parent zeolites, such as Si/Al ratio and crystallinity, is important for making mesoporous zeolites effectively.     

The influence of zeolite acidity for the coupled hydrogenation and ring opening of 1-methylnaphthalene on Pt/USY catalysts

The influence of framework and extraframework composition of USY zeolite on the catalytic performance of bifunctional Pt/USY (1 wt.% Pt) catalysts for the coupled hydrogenation and ring opening of 1-methylnaphthalene (1-MN) has been studied on a continuous fixed bed high pressure reactor. All Pt/USY catalysts showed very high methylnaphthalene (MN) conversions under the reaction conditions studied (T=300–375 °C, P=4.0 MPa, WHSV=2 h⁻¹, H₂/1-MN=30 mol/mol). Product yields and selectivities were mainly determined by the zeolite composition (i.e. acidity). Selectivity to products with the same number of carbon atoms than the feed (C11) increased, at constant temperature, with decreasing the Brönsted acidity of the USY zeolite, that is, with decreasing the concentration of framework Al (FAL) and increasing extraframework Al (EFAL). Selectivity to high cetane ring opening products (ROP=C11-alkylbenzenes (C11AB) and C11-alkylcycloalkanes) within the C11 fraction was higher for the less acidic catalysts. A maximum yield of ROP of ca. 15 wt.% at a C11 yield of ca. 73 wt.% was obtained at 350 °C (P=4.0 MPa, WHSV=2 h⁻¹, H₂/1-MN=30 mol/mol) for a USY zeolite with an intermediate degree of dealumination (a₀=24.33 Å) and containing all the EFAL (bulk Si/Al ratio of 2.6). For this catalyst, a slight increase in ROP yield (ca. 17 wt.%) at similar C11 yield (ca. 74 wt.%) was obtained by working at lower temperature (300 °C) and lower space velocity. Increasing the reaction pressure above 4.0 MPa had only a marginal influence on product yields and selectivities.     

One-electron reducibility of isolated copper oxide on alumina for selective NO–CO reaction

The H₂-TPR (temperature-programmed reduction) study was performed for supported copper oxide catalysts with low loading (0.5 wt% as copper). Among the various kinds of support materials (γ-Al₂O₃, TiO₂, ZrO₂, SiO₂, ZSM-5), alumina-supported copper oxide indicated a one-electron reduction behavior of Cu²⁺ into Cu⁺ ions in the presence of H₂. The reduction of the isolated Cu²⁺ species in a tetragonally distorted octahedral symmetry into the low coordinated Cu⁺ ions was identified by means of X-ray absorption spectroscopy (XANES and EXAFS). The isolated Cu⁺ ions hosted by γ-Al₂O₃ surface were prevented from further reduction into metallic Cu⁰ state under reducing condition with H₂ at 773 K. Less dispersed supported copper oxide species were easily reduced to Cu⁰ metal particles with H₂ at 573 K regardless of the kinds of support materials. It is suggested that the one-electron redox behavior of the isolated copper oxide species over γ-Al₂O₃ promotes the catalytic reduction of NO with CO in the presence of oxygen on the basis of redox-type mechanism between Cu²⁺ and Cu⁺ in atomically dispersed state.     

Studies of Cu-ZSM-5 by X-ray absorption spectroscopy and its application for the oxidation of benzene to phenol by air

The oxidation of benzene to phenol has been successfully carried out in air over Cu-ZSM-5 at moderate temperatures. Several parameters such as Cu loading, calcination temperature and co-exchanged metal ions influence the nature of the catalyst. At low Cu loadings, the catalyst is more selective to phenol while at high Cu loadings CO₂ is the major product. In situ H₂-TPR XAFS studies reveal that at low Cu loadings, Cu exists as isolated pentacoordinated ions, with 4 equatorial oxygens at 1.94 Å and a more distant axial oxygen at 2.34 Å. At higher loadings, monomeric as well as dimeric Cu species exist, with a Cu–Cu distance of 2.92 Å. This suggests that the isolated Cu sites are the active sites responsible for phenol formation. When the catalyst was calcined at 450 °C, the activity peaked in the first hour and then slowly deactivated, but when the calcination temperature was increased to 850 °C, the activity slowly increased until it reached a plateau. Analysis of the XANES region during in situ H₂-TPR shows that at lower calcination temperatures two reduction peaks are present, corresponding to Cu²⁺ → Cu⁺ and Cu⁺ → Cu⁰. At high calcination temperatures, only a small fraction of the Cu undergoes the two-step reduction and most of the Cu remains in the +2 state. Slow deactivation of the catalyst calcined at 450 °C is due to migration of the Cu ions to inaccessible sites in the zeolite; at high calcination temperatures the Cu is tightly bound to the framework and is unable to migrate. EXAFS analysis of the sample calcined at 850 °C reveals two Cu–Si(Al) scattering paths at 2.83 Å. Doping the catalyst with other metals, in particular Ag and Pd, further improves the activity and selectivity of the reaction. The addition of water to the reaction increases the selectivity of the reaction by displacing the product from the active site.