Synthesis of acid–base bifunctional CaO/ITQ-2 zeolite catalyst for phosphorylation of dodecanol

A series of acid–base bifunctional CaO/ITQ-2 zeolite catalysts were prepared by introducing calcium into the ITQ-2 zeolite. The catalysts were characterized by X-ray diffraction, FT-IR, NH₃-TPD and CO₂-TPD. The characterization results proved that ITQ-2 zeolite was synthesized by delaminating the MCM-22 zeolite. After modification by CaO, the catalysts could simultaneously have alkaline and acidic sites with little structural change. We then studied the catalytic capabilities of the prepared catalysts in the phosphorylation of dodecanol to di-dodecyl phosphate (DAP). The results show that ITQ-2 catalyst has higher selectivity for DAP than MCM-22. Versus ITQ-2 zeolite, the CaO/ITQ-2 catalysts have excellent acid–base cooperativity. The conversion of phosphoric acid and the selectivity of di-dodecyl phosphate could reach 80.2% and 77.5%, respectively over 3 wt.%CaO/ITQ-2 at optimal conditions. The catalytic activity of CaO/ITQ-2 catalyst could be regenerated by roasting after four times of reusing.     

Effect of Ru addition to Co/SiO2/HZSM-5 catalysts on Fischer–Tropsch synthesis of gasoline-range hydrocarbons

Microporous HZSM-5 zeolite and mesoporous SiO₂ supported Ru–Co catalysts of various Ru adding amounts were prepared and evaluated for Fischer–Tropsch synthesis (FTS) of gasoline-range hydrocarbons (C₅–C₁₂). The tailor-made Ru–Co/SiO₂/HZSM-5 catalysts possessed both micro- and mesopores, which accelerated hydrocracking/hydroisomerization of long-chain products and provided quick mass transfer channels respectively during FTS. In the same time, Ru increased Co reduction degree by hydrogen spillover, thus CO conversion of 62.8% and gasoline-range hydrocarbon selectivity of 47%, including more than 14% isoparaffins, were achieved simultaneously when Ru content was optimized at 1 wt% in Ru–Co/SiO₂/HZSM-5 catalyst.     

Differences between ZSM-5 and ZSM-11 zeolite catalysts in 1-hexene aromatization and isomerization

ZSM-5 and ZSM-11 zeolites with high crystallinity are synthesized and tested in the aromatization and isomerization reactions of 1-hexene at 370 °C in a continuous flow fixed bed. The results indicate that ZSM-5 and ZSM-11 zeolites possess similar acid site amount and strength, and most of the acid sites belong to Brønsted acid. When the ZSM-5 and ZSM-11 zeolites were used as catalysts, the aromatics selectivity over ZSM-11 catalyst was higher than that over ZSM-5 catalyst in contrast to i-paraffins selectivity, maybe attributed to that the C₇ and C₈ aromatics have an easier exit from the ZSM-11 zeolite. Moreover, the decrease of particle size can present superior aromatics selectivity and less i-paraffins selectivity in the aromatization and isomerization of 1-hexene over the ZSM-11 catalyst.     

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO₂ adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na⁺ cations in the same positions the isosteric adsorption heats of CO₂ adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO₂/Na⁺ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.     

Exploring suitable ZSM-5/MCM-41 zeolites for catalytic cracking of n-dodecane: Effect of initial particle size and Si/Al ratio

In this study, various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5. The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied. The results of XRD, TEM N₂-adsorption-desorption, NH₃-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals, and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5. Catalytic cracking of n-dodecane (550 ℃, 4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance, with the improvement higher than 87% in the catalytic activities and 21% in the deactivation rate compared with untreated zeolites. This could be ascribed to their suitable pore structure, which enhanced the diffusion of reactant molecules in pores of catalysts.     

Syngas to iso-paraffins over Co/SiO2 combined with metal/zeolite catalysts

Selective production of gasoline ranged iso-paraffins from synthesis gas was performed in a consecutive dual reactor system, in which Fischer–Tropsch reaction was carried out over Co/SiO₂ catalyst in the upper reactor and hydroconversion of the Fischer–Tropsch hydrocarbons occurred over precious metal/zeolite catalyst in the lower reactor. Results indicate that the product distribution of traditional Fischer–Tropsch synthesis was significantly modified and high selectivity to iso-paraffins was achieved with the presence of metal/zeolite catalyst in the lower reactor. A significant effect of metals (Pt and Pd), zeolites (zeolites of β and USY), and the preparation methods (impregnation and ion exchange) of the metal/zeolite catalyst on the iso-paraffins selectivity and product distribution was clearly observed. This was explained based on the property of the metal for hydrogen spillover and the acidic and structural properties of the zeolite in the bifunctional metal/zeolite catalyst.     

Catalytic behavior of CoMo/ZSM5 catalysts for CS2 conversion

Catalysts based upon ZSM-5 zeolites (SiO₂/Al₂O₃ molar ratio of 30 and 150) were synthesized and tested for the carbon disulfide (CS₂) conversion. First, the zeolites were shaped in pellets using alumina (20 wt%) as binder. The pellets containing ZSM5 (SiO₂/Al₂O₃ = 30) were exchanged with Co²⁺. Afterwards, this material and the other one, having the zeolite with SiO₂/Al₂O₃ ratio of 150, were co-impregnated with Mo and Co salts. The structural variations were explored by means of X-Ray Diffraction. The progressive reduction of the metal phases was studied by Thermal Programmed Reduction (TPR); the acidity distribution was evaluated by FTIR-pyridine adsorption and the aggregation state of the crystalline phases was characterized by High Resolution Transmission Electron Microscopy (HRTEM) and EDS. The catalytic properties were evaluated in a fixed bed reactor at 350 °C, P = 20 kg/cm² with a H₂/CS₂ molar ratio equal to 2. The results suggest a hindering of catalytic activity by the metal phase, which is deposited either on the alumina or over the external surface of the zeolite crystallites.     

Synthesis of ITQ-2 Zeolites and Catalytic Performance in n-Dodecane Cracking

ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction, scanning electron microscopy, nitrogen adsorpti...     

Synthesis and Catalytic Reactivity of MCM-22/ZSM-35 Composites for Olefin Aromatization

A series of MCM-22/ZSM-35 composites has been hydrothermally synthesized and characterized by XRD, SEM, particle size distribution analysis, N₂ adsorption and NH₃-TPD techniques. Pulse and continuous flow reactions were carried out to evaluate the catalytic performances of these composites in aromatization of olefins, respectively. It was found that MCM-22/ZSM-35 composites could be rapidly crystallized at 174 °C with an optimal gel composition of SiO₂/Al₂O₃=25, Na₂O/SiO₂=0.11, HMI/SiO₂=0.35, and H₂O/SiO₂=45 (molar ratio), of which the weight ratio of ZSM-35 zeolite in the composite relied on the crystallization time. The coexistence of MCM-22 and ZSM-35 in the composite (MCM-22/ZSM-35=45/55 wt/wt) was observed to exert a notable synergistic effect on the aromatization ability for butene conversion and FCC gasoline updating, possibly due to the intergrowth of some MCM-22 and ZSM-35 layers.     

Organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite

A series of ZSM-5/ZSM-11 co-crystalline zeolites with various compositions and morphologies were successfully synthesized via an organic template-free hydrothermal route and characterized by XRD, XRF, SEM, NMR and N₂ adsorption/desorption technologies. The effects of raw materials and batch composition were investigated systematically. Various silicon sources can be employed in the organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite, however only a few types of aluminum sources are available. This organic template-free system is favorable to the aluminum-rich zeolite. With the increase of initial SiO₂/Al₂O₃ ratio, the ZSM-5 percentage in the ZSM-5/ZSM-11 co-crystalline zeolite increases as well as the crystal size, and especially the morphology of ZSM-5/ZSM-11 co-crystalline zeolite prepared from the colloidal silica-NaAlO₂ solution system changes gradually from nano-rod aggregation, micro-spindle to single hexagon and then to twinned hexagon crystals. Moreover, Na⁺ and OH⁻ in the initial materials can promote the nucleation of the ZSM-5/ZSM-11 co-crystalline zeolite significantly and are beneficial to the formation of crystals with relatively low length/width ratio, while K⁺ postpones the crystallization process seriously.     

Activity of different zeolite-supported Ni catalysts for methane reforming with carbon dioxide

The catalytic performance of Ni based on various types of zeolites (zeolite A, zeolite X, zeolite Y, and ZSM-5) prepared by incipient wetness impregnation has been investigated for the catalytic carbon dioxide reforming of methane into synthesis gas at 700 °C, at atmospheric pressure, and at a CH₄/CO₂ ratio of 1. It was found that Ni/zeolite Y showed better catalytic performance than the other types of studied zeolites. In addition, the stability of the Ni/zeolite Y was greatly superior to that of the other catalysts. A weight of Ni loading at 7 wt.% showed the best catalytic activity on each zeolite support; however, the 7% Ni catalysts produced a higher amount of coke than that of two other Ni loadings, 3 and 5%.     

C-radioisotope labeled methanol conversion over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve

The Na–MCM-41 mesoporous molecular sieve, Na–ZSM-5 and Na–Beta zeolites have been modified by Cs- and H- using ion-exchange method and characterized by XRD, SEM and nitrogen adsorption. The conversion of methanol was studied over H- and Cs- modified ZSM-5, Beta zeolites and MCM-41 mesoporous molecular sieve. Methanol was in ¹¹C-radioisotope labeled form in-order to follow its conversion during the catalytic process, since the radioactivity method provides a very sensitive detection possibility to investigate the conversion of small amounts of methanol and some intermediates at different reaction times and temperatures. The understanding of reaction mechanism is important for side-chain methylation over Cs–zeolite catalysts by methanol, as they are more selective than other alkali exchanged zeolites (Li, Na and K). The reaction pathway of the transformation of methanol to hydrocarbons and aldehydes has been elaborated.     

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C₈ fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores.     

Investigation of Small-Pore Zeolites via Vapor-Phase Adsorption of n-Hexane

Cage-based small-pore zeolites are promising catalysts for catalytic applications such as methanol-to-olefins to produce light olefins and selective catalytic reduction to mitigate NO_x emissions. The present paper reports our recent studies on vapor-phase adsorption of n-hexane in a series of small-pore zeolites with cages such as 3A, 4A, 5A, ITQ-29, SSZ-13, SSZ-16, SSZ-17, SSZ-36, SSZ-50, ITQ-12, ZK-5, and Rho. The effects of zeolite compositions and crystal sizes on the adsorption kinetics and capacity are investigated, demonstrating that n-hexane adsorption is a useful tool for characterizing the effective pore sizes and volumes of small pore zeolites.     

Structural Effects of HZSM-5 Zeolite on Methanol-to-Propylene Reaction

ZSM-5 zeolite was synthesized using n-butylamine as a template under hydrothermal conditions. The morphology of the prepared zeolites was changed with the initial gel composition. The influences of OH⁻/template and H₂O/template ratios on the morphology, mesoporosity, acid properties, and crystal size of the synthesized zeolites were evaluated, also the structural effects of the prepared zeolites on the catalytic performances of the methanol-to-propylene process. Increasing the external surface area and mesopore volume of the catalysts improved the propylene selectivity. A direct relationship between the deactivation of catalysts and their acidic properties was found. The results were derived from laboratory data and need to be re-examined on a larger scale to ensure their accuracy on an industrial scale.     

Synthesis of ZSM-5 type zeolites with and without template and evaluation of physicochemical properties and aniline alkylation activity

ZSM-5 zeolite containing SiO₂/Al₂O₃ = 28 was synthesised by hydrothermal process with and without template. Characterisation of the zeolites was done using XRD, IR, NMR, SEM and BET surface area measurements. Acidity of the zeolites was measured by ammonia adsorption-desorption. Catalytic activity of HZSM-5 zeolites was evaluated by aniline alkylation, cumene dealkylation, alkylation of benzene with ethylene and propylene and isomerisation ofm-xylene. Catalytic activity is discussed from the point of view of zeolite acidity and morphology.     

不同结构分子筛的甲醇制丙烯催化性能

在常压、空速为1.5 h^-1、反应温度为450℃条件下,考察了4种具有不同拓扑结构的分子筛(SAPO-34、ZSM-48、ZSM-5和beta)在甲醇转化制丙烯(MTP)反应中的催化性能,并对催化剂的积炭失活行为进行了研究。结果表明,从8元环到12元环,分子筛孔口尺寸越小,低碳烯烃(乙烯+丙烯)选择性越高,积炭失活速率也越快。孔道尺寸越大,丙烯/乙烯(P/E)比越高,但产物分布向C₄以上组分偏移,丙烯选择性降低。10元环分子筛具有较高的丙烯选择性,但催化剂的积炭失活速率随孔道体系的不同有很大差异。一维直通孔道的ZSM-48容易积炭失活,而具有三维交叉孔结构的ZSM-5表现出了优异的抗积炭失活性能。不同结构分子筛在MTP反应中催化性能的差异主要归因于分子筛的过渡态择形和产物择形作用的不同。     

Direct synthesis of iso-paraffins from syngas with slurry phase reaction

The direct synthesis of gasoline-range iso-paraffins from synthesis gas (CO + H₂, syngas) via modified Fischer–Tropsch (FT) reaction was investigated in the slurry phase reaction system, the contact state of hybrid catalyst components and the composition of hybrid catalyst were optimized in this reaction system. The results show that the FT reaction and the in situ hydroconversion of its products occurred over hybrid catalysts containing Co/SiO₂, very high selectivity of gasoline-range iso-paraffins could be achieved.     

The influence of physicochemical properties of ZSM-5 on catalytic dewaxing

A decrease in the crystallite size increases the activity as well as the selectivity and reduces the deactivation of ZSM-5 zeolites in the dewaxing of petroleum fractions. Isomorphous replacement of Al³⁺ by Fe³⁺ reduces the dewaxing activity but enhances the yield of dewaxed oil and gasoline at the expense of C₁-C₄ gases. Within limits, the Si/Al ratio does not affect the performance of ZSM-5 zeolite in the hydrodewaxing process.     

Gas Separation Properties of Polyimide-Zeolite Mixed Matrix Membranes

Mixed matrix membranes (MMMs) of polyimide (PI) and zeolite 13X, ZSM-5 and 4A were prepared by a solution-casting procedure. The effect of zeolite loading, pore size, and hydrophilicity/hydrophobicity of zeolite on the gas separation properties of these mixed matrix membranes were studied. Experimental results indicate that permeability of He, H₂, CO₂, and N₂ increased with zeolite loadings. Selectivity of H₂/N₂ shows a slight improvement for low loadings of zeolites 13X and ZSM-5 but has a decreasing trend for zeolite 4A and high loadings of zeolites 13X and ZSM-5. In addition, selectivity of H₂/CO₂ remains low (1–3) while selectivity of CO₂/N₂ is significantly improved with the incorporation of the three zeolites in the polyimide membrane. Experimental permeabilities are higher than those predicted by the Maxwell model except for H₂ and N₂ permeabilities of the PI-4A system which are consistent with the predicted permeabilities. The proposed modified Maxwell model is capable of predicting the permeabilities of polyimide-zeolite 4A MMMs, but fails to simulate the permeability increase induced by interface voids in the polyimide-zeolite 13X and ZSM-5 systems.