Effects of binder, coking and regeneration on acid properties of H-mordenite during TDP reaction

The effects of binder, coking and regeneration on the acid properties of H-mordenite zeolite during toluene disproportionation reaction (TDP) have been investigated by solid-state ³¹P-MAS-NMR of various adsorbed phosphorous probe molecules in conjunction with elemental analysis by ICP-MS technique. A series of fresh, spent and regenerated mordenite-based commercial catalysts were examined and the results were also compared with binder-free H-mordenite zeolite and unformulated γ-alumina binder. It is found that parent H-mordenite zeolite possessed only Brønsted acidity, which is responsible for the observed catalytic activity. In contrast, the γ-Al₂O₃ binder exhibited only Lewis acidity and plays a minor role during the catalytic reaction. While the amount of strong Brønsted acid sites decreased rapidly during initial coking, it reached a plateau at a total coke content of ca. 7 wt%, corresponding to ca. 80% decrease in total acidity. That the catalyst remained active even under deep coke deposition (>7 wt%) condition indicated catalytic activity may be invoked by subsequent coking taking place on the external surface rather than intracrystalline channels of the zeolite catalyst. Furthermore, upon catalyst regeneration treatment, ca. 75% of the total acidity could be effectively recovered.     

分子筛催化剂的失活与积炭

分子筛催化剂的失活与积炭刘中民，陈国权，王清遐，梁娟，蔡光宇（中国科学院大连化学物理研究所，大连１１６０２３）关键词分子筛，结炭，催化剂失活，甲醇转化，ＨＺＳＭ－５结炭是酸性分子筛催化剂失活的主要因素．本文通过具有碳链增长、环化、烷基化等多种反应途径...     

Experimental study on coking, deactivation, and regeneration of binderless 5A zeolite during 1-hexene adsorption

Coking, deactivation, and regeneration of 5A zeolite during 1-hexene adsorption were studied on a fixed-bed adsorber and a themogravimetric analyzer. Adsorption activity measurement, scanning electron microscope (SEM) analysis, X-ray diffraction (XRD) analysis, FT-IR analysis, ¹H NMR analysis, and porosity measurement were used to reveal the mechanism of coking and deactivation of 5A zeolite, and evaluate the influences of binder on them. There are distinct increases in both coke content and deactivation degree with increasing the adsorption temperature. Deactivation degrees of zeolite increase as coke contents rise, however, they display smaller increasing rate at higher coke content. The rates of coke formation and deactivation of 5A zeolite are significantly enhanced by the binder mainly due to the fact that the activity sites offered by the amorphous compounds contained in the binder catalyze the formation of coke precursors. As compared to the coke formed in zeolite with binder, the coke in binderless zeolite is more aromatic. The coke which consists of inflammable part and nonflammable part can be oxidatively removed completely while the temperature approaches 787 K. No destruction in 5A zeolite crystal structure was observed in the regenerated binderless sample. The formation of coke during 1-hexene adsorption on zeolite can be explained using the carbonization-cyclization reaction mechanism. Furthermore, the kinetics models for formation and removal of coke were developed.     

Regeneration of C4H10 dry reforming catalyst by nonthermal plasma

Carbon deposition via coke formation is one of the critical problems causing catalyst deactivation during the reforming of hydrocarbons. An effort was made to regenerate the catalyst (Ni/γ-alumina) by oxidation methods. Two approaches were carried out for the regeneration of the deactivated catalyst. The first one involves the plasma treatment of the deactivated catalyst in the presence of dry air over a temperature range of 300～500 °C, while the second one only the thermal treatment in the same temperature range. The performance of the regenerated catalyst was evaluated in terms of C₄H₁₀ and CO₂ conversions and the physicochemical characteristics were examined using a surface area analyzer, an elemental analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that the carbon deposit (coke) on the catalyst was about 9.89 wt% after reforming C₄H₁₀ for 5 h at 540 °C. The simple thermal treatment at 400 °C reduced carbon content to 6.59 wt% whereas it was decreased to 3.25 wt% by the plasma and heat combination. The specific surface area was fully restored to the original state by the plasma-assisted regeneration at 500 °C. As far as the catalytic activity is concerned, the fresh and regenerated catalysts exhibited similar C₄H₁₀ and CO₂ conversion efficiencies.     

Catalytic cracking of polyethylene over nanocrystalline HZSM-5: Catalyst deactivation and regeneration study

In this work, catalytic cracking of low density polyethylene (LDPE) over nanocrystalline HZSM-5 zeolite in a batch reactor at 340 °C was carried out with the aim of study both the catalyst resistance to deactivation and the catalyst regeneration process. For looking into the catalyst deactivation, consecutive polyethylene cracking experiments were carried out. Subsequently, the same reactions has been also performed but by regenerating the zeolite after each experiment by promoting coke combustion at 550 °C under air flow. Zeolites used were two samples of nanocrystalline HZSM-5 with very different textural properties (sample A, with most of its surface corresponding to zeolitic micropores and sample B with a considerable amount of external surface, mesopores and super-micropores) in order to study the effect of their textural properties in the deactivation and regeneration experiments. Although conversion and activity values reached over both samples are quite high taking into account the mild conditions used, sample B shows a very much higher initial activity than A due to its improved textural properties. In both samples two different deactivation mechanisms occur: a reversible deactivation by coke deposition removable by the regeneration procedure, and an irreversible or permanent deactivation by other factors. Deactivation of sample B occurs faster due to the higher amount of coke deposited on this material. However, the improved textural properties of this catalyst supposes an advantage for the regeneration process, since coke deposited either on the external surface or on the super-micropores and mesopores, makes easier the regeneration procedure.     

焦油催化裂化催化剂积炭失活的实验研究

对白云石、石灰石作用下生物质热解焦油催化裂化过程中的积炭失活问题进行了研究，考察了较长反应时间内催化剂积炭量和焦油转化率的变化情况。最长运行时间32 h，所得积炭质量分数为3%～15%，焦油转化率下降到70％左右。对不同来源焦油的生焦性、催化裂化反应条件等对积炭形成的影响作了考察，并从动力学角度对催化活性与积炭量之间的关系进行了分析，得到了单层积炭和多层积炭阶段线性和指数形式的关联式。     

柠檬酸改性Hβ分子筛上的苯与丙烯烷基化反应

研究了柠檬酸改性对Hβ分子筛上苯与丙烯烷基化反应性能的影响。通过比较分析改性前后催化剂寿命、二异丙苯选择性及其异构体组成分布等的变化。结果表明，二异丙苯的选择性及各异构体的分布与催化剂的酸密度和酸强度有关；较高酸密度和酸强度有利于烷基转移反应的进行，但却加快了催化剂的失活。柠檬酸改性处理可调节Hβ分子筛的酸密度和酸强度，改善苯烷基化的催化反应性能。经0.50mol/L的柠檬酸处理后，Hβ催化剂的寿命比原来延长30%，正丙苯的质量分数减少90%。     

合成气一步法制备液化石油气单管实验研究

采用甲醇合成催化剂与脱水催化剂机械混合,制备了液化石油气(LPG)合成催化剂。以模拟生物质气为原料气,在固定床单管实验装置上,温度(220~330 ℃)、压力(1.2~5.1 MPa)和空速(500~3 000 h^-1)条件下考察催化剂的性能。结果表明,在325 ℃、2.1 MPa、1 500 h^-1条件下,CO转化率达到72.36%,LPG占烃类产物的71.21%。当设定温度为325 ℃、压力2.1 MPa时、空速≤2 500 h^-1时,系统可以稳定运行;空速达到3 000 h^-1时,反应器内部温度迅速升高无法控制,造成催化剂烧结失活。针对上述催化剂,采用NH₃-TPD、XRD、N₂吸附-脱附和TPO对催化剂进行了表征。结果表明,催化剂的积炭、强酸位酸性降低及比表面积的降低是导致催化剂活性降低的重要影响因素。     

Synergistic effect of dealumination and ceria impregnation to the catalytic properties of MOR zeolite

MOR zeolite has been extensively employed as a catalyst in industries. However, high Brønsted acidity in MOR leads to rapid deactivation due to coke deposition on the pore mouths; thus, the surface acidity of MOR needs to be moderated. Herein, we report a modification of MOR chemical composition via acid treatment and deposition of ceria nanoparticles using a wet impregnation method. The acid treatment successfully increases the Si/Al ratio of MOR from 8.39 to 11.58 and reduces the total acid site concentration of MOR from 990 μmol/g to 752 μmol/g. The acidity of MOR is decreased when the Si/Al ratio is increased since the quantity of Brønsted acid sites is proportional to the number of Al framework. In addition, the acid treatment also improves the external surface area of MOR. Furthermore, ceria particles were successfully deposited on the MOR surface using wet impregnation method. The ceria content of parent MOR sample is lower compared to that of preceded by the acid treatment, which may be attributed to the formation of more terminal silanol groups. Finally, catalytic test on Friedel–Crafts alkylation of toluene with benzyl alcohol shows that the synergy between dealumination and the impregnation of ceria significantly improves the activity of MOR zeolite.     

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.     

乙烯在ZSM-5催化剂上低聚反应规律的研究

在固定床微反装置上,采用ZSM-5分子筛催化剂,考察了不同条件下乙烯的低聚反应。结果表明,适宜的条件可以抑制副反应,提高产物中丙烯与丁烯的选择性。随反应时间的延长,催化剂因积炭而失活,乙烯转化率由初始的96.2%降至6h后的41.1%,丙烯和丁烯选择性增加。提高乙烯空速可有效抑制氢转移反应从而提高烯烃选择性,根据不同转化率对应的产物分布,得到了ZSM 5催化剂上乙烯低聚的反应路径。乙烯转化率随反应温度的升高先增加后降低,500℃时达到最大值为88.0%,主要产物LPG组分中烷烃居多。提高反应压力有利于低聚反应进行,可以显著提高乙烯转化率,但不利于生成丙烯和丁烯。     

Non‐Oxidative Methane Conversion Using Lead‐ and Iron‐Modified Albite Catalysts in Fixed‐Bed Reactor

Raw and modified albite catalysts, including Pb/Albite and Fe/Albite catalysts, have been investigated for methane conversion to C₂ hydrocarbons under non‐oxidative conditions. Introduction of Pb to albite improved the activity and selectivity to non‐coke products. Based on characterization, it was found that Pb entered into the alkali and alkaline‐earth metal sites of albite, while partial Fe doped in the tetrahedron sites and the other loaded on the surface of albite. At the reaction temperature of 1073 K, methane gas hourly space velocity (GHSV) of 2 L·gcat^–1·h^–1, catalyst dosage of 0.25 g (300 mesh), the methane conversion catalyzed by raw albite in the fixed‐bed micro reactor exhibited a methane conversion of 3.32%. Notably, introducing a Pb content of 3.4 wt% into albite greatly enhanced the conversion of methane up to 8.19%, and the selectivity of C₂ hydrocarbons reached 99% without any coke under the same reaction conditions. While Fe‐doping could weakly heighten the methane conversion to 3.97%, and coke was formed. Thus, a comparison of Pb/Albite and Fe/Albite catalysts demonstrates that the catalytic activity of albite is mainly decided by alkali and alkaline‐earth metal sites, and lead‐modification can effectively improve the catalytic activity of albite.     

高硅ZSM-5原粉的外表面改性及其在甲醇制丙烯反应中的应用

使用来源广泛的甲醇为原料制取丙烯, 是对石油路线生产丙烯的重要补充. 尽管以ZSM-5分子筛为催化剂的固定床甲醇制丙烯(MTP)技术已经实现了工业应用, 但进一步提高催化剂的寿命和丙烯的选择性一直是学术界和工业界的研究热点. MTP过程作为典型的酸催化反应, 积碳是催化剂失活的主要原因, 由于ZSM-5分子筛十元环孔道的空间限制作用, 积碳主要分布在外表面. 因此, 消除外表面的酸性位点对延长催化剂的寿命至关重要, 但修饰外表面酸性位点的同时往往会改变样品的其他性质, 如孔径、整体酸量等. 本文分别使用Na2H2EDTA和H3PO4处理高硅ZSM-5分子筛原粉(微孔内含有机模板剂)来选择性地减小或消除外表面的酸密度, 而不影响分子筛内部的性质, 并考察了处理后样品的MTP性能. 使用N2物理吸附、SEM和27Al MAS NMR表征样品的织构性质、形貌和Al原子的化学环境, XPS和三异丙苯裂解实验表征外表面的硅铝比和酸密度. 表征结果表明, Na2H2EDTA处理虽然可以选择性的脱除表面Al原子, 但会在外表面产生新的酸点(可能是硅巢). H3PO4处理虽然不能脱除表面的Al原子, 但外表面残留的P物种能够有效的减小酸密度. MTP评价结果表明, H3PO4处理能够有效的延长催化剂的寿命和维持丙烯的选择性, 这是因为H3PO4处理既提高了外表面的容碳能力, 也抑制了积碳沉积的速率. Na2H2EDTA处理仅能增加外表面的容碳能力, 所以其只能延长催化寿命. 通过进一步优化H3PO4后处理的条件, 处理后的ZSM-5样品的催化寿命可以延长至前体的1.5倍, 同时, 丙烯的选择性也略有提高, 并且在失活前维持增加的趋势.     

Mechanism of Coke Influence on the Catalytic Activity of FeZSM-5 in the Reaction of Benzene Oxidation into Phenol

The influence of coke formation in the reaction of benzene oxidation by nitrous oxide into phenol on the catalytic activity and concentration of iron-containing active sites (-sites), which are stabilized in the microporous structure of FeZSM-5 zeolite, is studied. The deactivation by coke is explained by the poisoning of -sites, whose concentration decreases linearly with an increase in the coke content, rather than by the blocking of zeolite pores. The activity per one -site remains unchanged. This fact indicates the absence of diffusion limitations associated with coke formation. The toxicity of coke for the -sites is determined. The coke amount equivalent to 100–120 benzene molecules is shown to result in the deactivation of one active site.     

Co改性Mo/MCM-22催化剂上甲烷无氧芳构化及积炭研究

 研究了Co的添加对Mo／MCM－22催化剂甲烷无氧芳构化反应性能的影响．发现用共浸渍法制备的Co／Mo摩尔比为0．2的催化剂具有较高的活性,而先浸渍Mo后浸渍Co的催化剂具有较好的稳定性．XRD实验表明,Co及Mo的氧化物均高度分散在分子筛表面,其担载降低了分子筛的衍射强度．不同接触时间下催化剂的反应结果表明,接触时间长,积炭选择性随接触时间增加而迅速增加;接触时间短,积炭选择性随接触时间增加而减少．积炭催化剂的TG研究表明,催化剂上的积炭主要有两种形式．低温积炭随反应时间增加而迅速增多,高温积炭的变化则较为缓慢．低温积炭可能是导致催化剂活化和失活的主要原因．高温积炭可能是一种大分子量的碳氢物种,位于MCM－22分子筛的“超笼”中,表明MCM－22有较大的容积炭能力．     

Zn/SiO_2气相催化裂解1,1,2-三氯乙烷脱HCl:酸性与失活

用浸渍法制备了一系列SiO_2负载的过渡金属催化剂M/SiO_2(M为第Ⅳ周期过渡金属),用于气相催化裂解1,1,2-三氯乙烷(TCE)脱HCl的反应。研究发现,在M/SiO_2催化剂中,Zn/SiO_2催化性能最好,TCE转化率能达到98%,顺-1,2-二氯乙烯(cis-DCE)的选择性为82%。随着Zn负载量的增加,Zn/SiO_2催化剂上TCE转化率逐渐增加,与催化剂上总酸量变化一致。将总酸量以Zn负载量归一化得到比酸量,则比酸量越大,Zn/SiO_2催化剂比活性越高,表明Zn/SiO_2催化剂表面酸性中心是TCE脱氯反应的活性中心。Zn/SiO_2催化剂在TCE脱HCl反应中存在一定的失活现象,归因于反应过程中催化剂表面积炭。低Zn负载量催化剂上会产生较多积炭,归因于其具有较多强酸性中心,表明催化剂表面强酸中心是导致催化剂积炭和失活的主要原因。     

提高USY型FCC催化剂硫转移和催化裂化活性的研究

采用镁、铈、镧和磷对USY型FCC催化剂进行改性，采用FT IR分析方法对改性催化剂的表面酸性进行了表征，研究了硫转移活性组分对催化剂的硫转移和催化裂化活性的影响。结果表明，多次氧化 还原循环后，改性催化剂仍保持较好的硫转移活性，可以达到60%以上。镁的引入会减少基质和分子筛表面强酸的数量，少量镁的引入对催化裂化活性影响不大，铈和镧的引入会使分子筛和基质的表面酸量得到显著增加，提高催化裂化活性，但同时会引起焦炭的增加，磷改性可改善基质和分子筛表面酸性，抑制焦炭的产生，保持催化裂化活性的同时使汽油中的烯烃质量分数下降6%。     

甲烷在Mo/HZSM-5催化剂上的脱氢聚合反应

对不同Mo含量的Mo／HZSM－5催化剂的结构进行了表征，并对这些催化剂的甲烷非氧气氛下的转化反应进行了考察．催化剂的BET比表面积及酸性随Mo含量的增加而降低，当Mo含量大于5％时，Mo对ZSM－5分子筛的晶型有影响，并出现MoO3物相．甲烷在700℃时可高选择性地生成苯和乙烯，最佳Mo含量大约为2％．纯的MoO3或HZSM－5上该反应几乎不进行，因此，可能是分散的钼氧离子和分子筛的酸中心是甲烷转化的活性中心，只有二者的协同作用才能促进甲烷的转化．反应后催化剂中的钼物种被还原了．催化剂上的积炭可能是催化剂失活的主要原因之一，烧炭后催化剂活性基本恢复．     

Fabrication of a nano-sized ZSM-5 zeolite with intercrystalline mesopores for conversion of methanol to gasoline

Carbon deposition during methanol to hydrocarbons leads to the quick deactivation of ZSM-5 catalyst and it is one of the major problems for this technology. Decreasing the crystal size or introducing mesopores into ZSM-5 zeolites can improve its diffusion property and decrease the coke formation. In this paper, nano-sized ZSM-5 zeolite with intercrystalline mesopores combining the mesoporous and nanosized structure was fabricated. For comparison, the mesoporous ZSM-5 and nano-sized ZSM-5 were also prepared. These catalyst samples were characterized by XRD, BET, NH3-TPD, TEM, Py-IR and TG techniques and used on the conversion of methanol to gasoline in a fixed-bed reactor at T = 405 °C, WHSV = 4.74 h-1and P = 1.0 MPa. It was found that the external surface area of the nano-sized ZSM-5 zeolite with intercrystalline mesopores reached 104 m2/g, larger than that of mesoporous ZSM-5(66 m2/g) and nanosized ZSM-5(76 m2/g). Catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores was 93 h, which was only longer than that of mesoporous ZSM-5(86 h), but shorter than that of nanosized ZSM-5(104 h). Strong acidity promoted the coke formation and thus decreased the catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores though it presented large external surface that could improve the diffusion property. The special zeolite catalyst was further dealuminated to decrease the strong acidity. After this, its coke formation rate was slowed and catalytic lifetime was prolonged to 106 h because of the large external surface area and decreased weak acidity. This special structural zeolite is a potential catalyst for methanol to gasoline reaction.     

Large Zeolite H‐ZSM‐5 Crystals as Models for the Methanol‐to‐Hydrocarbons Process: Bridging the Gap between Single‐Particle Examination and Bulk Catalyst Analysis

The catalytic, deactivation, and regeneration characteristics of large coffin‐shaped H‐ZSM‐5 crystals were investigated during the methanol‐to‐hydrocarbons (MTH) reaction at 350 and 500 °C. Online gas‐phase effluent analysis and examination of retained material thereof were used to explore the bulk properties of large coffin‐shaped zeolite H‐ZSM‐5 crystals in a fixed‐bed reactor to introduce them as model catalysts for the MTH reaction. These findings were related to observations made at the individual particle level by using polarization‐dependent UV‐visible microspectroscopy and mass spectrometric techniques after reaction in an in situ microspectroscopy reaction cell. Excellent agreement between the spectroscopic measurements and the analysis of hydrocarbon deposits by means of retained hydrocarbon analysis and time‐of‐flight secondary‐ion mass spectrometry of spent catalyst materials was observed. The obtained data reveal a shift towards more condensed coke deposits on the outer zeolite surface at higher reaction temperatures. Zeolites in the fixed‐bed reactor setup underwent more coke deposition than those reacted in the in situ microspectroscopy reaction cell. Regeneration studies of the large zeolite crystals were performed by oxidation in O₂/inert gas mixtures at 550 °C. UV‐visible microspectroscopic measurements using the oligomerization of styrene derivatives as probe reaction indicated that the fraction of strong acid sites decreased during regeneration. This change was accompanied by a slight decrease in the initial conversion obtained after regeneration. H‐ZSM‐5 deactivated more rapidly at higher reaction temperature.