Vapor phase isopropylation of quinoline over modified HY zeolites

The vapor phase isopropylation of quinoline was carried out over HY and modified HY zeolites in a fixed‐bed reactor at atmospheric pressure. The yield of 2‐isopropylquinoline was higher over modified zeolites, especially over doubly‐promoted LaKHY zeolite. The maximum yield of 2‐isopropylquinoline obtained was 48.8 wt% with 82.9% selectivity. The reaction favors on moderate Lewis acidic sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

Cyclohexylation of naphthalene over unmodified HY zeolites

Cyclohexylation of naphthalene was studied over four commercial unmodified HY zeolites. Approximately equal results were obtained on HY (ZF 515, ZF 520, CBV 720) zeolites. The best results were obtained with cyclohexylbromide as alkylating agent inn-nonane and inn-decane as solvents at boiling point. Conversion of naphthalene was max. 97%, 2,6-selectivity 43% and,'-selectivity 77%.     

Selective alkylation of aniline with methanol over metallosilicates

The selective alkylation of aniline with methanol was investigated over various metallosilicates synthesized in two different media: alkaline medium (NaOH) and fluorine medium (NH₄F). Through the elemental analysis, XRD, and²⁹Si MAS NMR, it was thought that all the metallosilicates had MFI zeolite structure and the metals were incorporated in metallosilicate framework successfully. Temperature programmed desorption (TPD) of NH₃ and aniline alkylation suggested that the selectivity for N,N-dimethylaniline (NNDMA) is high when the metallosilicates have a large number of medium acid sites (567–673 K), which means that the medium acid sites play an important role in the production of NNDMA. It was also known that metallosilicates synthesized in fluorine medium have strong acid sites (> 773 K) and were deactivated more rapidly than those synthesized in alkaline medium.     

改性Beta（Na）型分子筛对异丙醇苯酚烷基化反应的影响

本文研究了用Beta（Na）型分子筛及用Na2O、磷钨酸改性后的Beta（Na）型分子筛作催化剂对苯酚异丙醇烷基化反应的影响。采用NH3-TPD、X射线衍射对催化剂晶相和表面酸性进行表征。实验结果表明：用Na2O改性后催化剂基本失活,而用磷钨酸改性后转化率可达68.3165%,邻异丙基苯酚选择性可达59.9167%。     

硅油-硝酸镧复合改性ZSM-5催化剂上甲苯甲醇选择性烷基化反应性能

以HZSM-5为改性基体,甲基硅油为改性剂,采用浸渍法制备硅油改性催化剂SiHZ(3.0)和复合改性催化剂SiHZ(3.0)/La₂O₃,考察硅油-硝酸镧复合改性ZSM-5催化剂上甲苯甲醇选择性烷基化的反应性能,并与单纯硅油改性的ZSM-5催化剂进行比较,结合催化剂酸性和孔结构的表征,研究硅油-硝酸镧复合改性对催化剂性能的影响。结果表明,在反应初期复合改性SiHZ(3.0)/La₂O₃催化剂上,甲苯转化率略低于单纯硅油改性的SiHZ(3.0)催化剂,对二甲苯选择性相近;反应100 h后,SiHZ(3.0)/La₂O₃催化剂活性和选择性均高于SiHZ(3.0)催化剂,说明复合改性催化剂中La₂O₃在硅油修饰外表面和孔口的基础上,进一步调变孔道内酸性质,降低强酸中心量和B酸酸量,从而显著提高催化剂稳定性。     

t-Butylation of p-cresol with t-butyl alcohol over mesoporous Al-MCM-41 molecular sieves

Selective liquid-phase t-butylation of p-cresol with t-butyl alcohol (t-BuOH) to produce 2-t-butyl-p-cresol (TBC) has been conducted over Al-MCM-41 catalysts with different Si/Al ratios. The effects of various reaction parameters such as temperature, reaction time and n_t-BuOH:n_p-cresol ratio on the conversion of p-cresol and the selectivity of TBC have been systematically investigated as well. When the Si/Al ratio of Al-MCM-41 catalysts is increased from 21 to 104 (respectively yielding Al-MCM-41(21), Al-MCM-41(42), Al-MCM-41(62), Al-MCM-41(83) and Al-MCM-41(104)), both the conversion of p-cresol and the yield and selectivity of TBC decrease due to the decrease of the number of Brønsted acid sites of the Al-MCM-41 catalysts. Al-MCM-41(21) catalyst is found to give the highest conversion of p-cresol (88.2%) and the highest selectivity of TBC (90.40%) under the optimal n_t-BuOH:n_p-cresol mole ratio of 2:1, the optimal reaction temperature of 90 °C and the optimal reaction time of 2 h. Furthermore, Al-MCM-41(21) can be recycled up to at least four times without losing its catalytic performance for butylation reaction.     

Selective isomerization of isophorone oxide over zeolites

Ring-contracted main product formed by isomerization of isophorone oxide (1) is 2-formyl-2,4,4-trimethylcyclopentanone (2); a high yield of (2) could be achieved by use of zeolites as heterogeneous catalysts. The reaction could be carried out in a discontinuous liquid-phase batch reactor as well as in a continuous vapor-phase fixed-bed reactor. The formation of (2) by decarbonylation of (2) could be reduced by increasing the catalyst loading or by carrying out the reaction under short contact time in gas phase conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective synthesis of 2-methylquinoline over zeolites

The selective vapour-phase synthesis of 2-methylquinoline by alkylation of quinoline with methanol was carried out over HY, HZSM-5(30), CrHY, CeHY, LaHY, LaKHY and CeHZSM-5(30) zeolites in a fixed-bed reactor at atmospheric pressure. The yields of 2-methylquinoline over modified zeolites, especially those of doubly promoted LaKHY, were found to be higher than those of unmodified zeolites. The maximum yield of 2-methylquinoline obtained was 60.6 wt% at 91.5 wt% selectivity over LaKHY zeolite. The active sites responsible for this methylation were found to be more on Lewis acidic sites available over zeolite systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective toluene disproportionation over ZSM-5 zeolites

Selective toluene disproportionation to benzene and xylenes is investigated over HZSM-5 and modified HZSM-5 zeolites. The zeolites are modified with nickel, magnesium, phosphorus and boron, characterised by sorption, acidity measurement and X-ray photoelectron spectroscopy, and their activity towards toluene disproportionation is discussed in the light of their physico-chemical properties. The two types of active sites have been identified; one promoting disproportionation and the other cracking and dealkylation of toluene. It is found that the latter sites are suppressed due to incorporation of the modifiers. The modified zeolites are found to be para-selective which appears to be consistent with the commonly accepted view that modifiers like magnesium, phosphorus and boron reside in the channels and react with Brønsted acid sites, leading to partial blockages and thus favouring the formation of p-xylene. The effect of poisoning the zeolite with 1-methylisoquinoline is also investigated. In the case of poisoned catalyst, p-xylene is produced at levels up to 99%. The total elimination of other isomers from the products is suggested due to the selective poisoning of the non-selective sites (on the external crystal surface) and to partial blocking of the pore openings.     

Reactions of benzyl alcohol and dibenzyl ether over zeolites

The reaction of benzyl alcohol and dibenzyl ether on several zeolites was studied in the temperature range 300–500 °C. The major products were benzaldehyde and toluene due to disproportionation, anthracene due to intermolecular alkylation followed by cyclodehydration, benzyltoluenes due to alkylation followed by hydrogenolysis, and stilbene. The alkylation course was strongly influenced by shape selectivity with the large pore zeolites mainly yielding anthracene and the medium pore zeolites benzyltoluene. The formation of stilbene was a new observation which has a bearing on the mechanism of the methanol-to-hydrocarbon reactions.     

Side-chain alkylation of 2,6-lutidine to 2,6-divinylpyridine over basic zeolites

Synthesis of 2,6-divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) was achieved for the first time by side-chain alkylation of 2,6-lutidine using formaldehyde (37 wt/v) as alkylating agent in heterogeneous conditions at atmospheric pressure, and at a reaction temperature of 300 °C over alkali and alkaline metal ion modified zeolites. A mixture of 2,6-divinylpyridine and 2-methyl,6-vinylpyridine were formed by the alkylation of the 2,6-lutidine over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of 2,6-lutidine was studied over various potassium metal ion modified zeolite molecular sieves like ZSM-5 (30), X, Y, mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2,6-lutidine when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) gave best conversion of 2,6-lutidine and selectivity to 2-methyl,6-vinylpyridine. K-ZSM-5 (30) catalyst was employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2,6-lutidine. The effect of potassium metal ion content and precursors of potassium ion on catalytic activity in side-chain alkylation of 2,6-lutidine was studied. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed mechanism. The selectivities of 2,6-DVP were 45.2, 40.0, and 30.7% at 73.4, 66.0 and 60.5% conversion at 300 °C from 2,6-lutidine and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and Cs-K-ZSM-5 (30), respectively.     

Vapour phase synthesis of 3,5-dipropylpyridine over modified zeolites

3,5-Dipropylpyridine was synthesized selectively in vapour phase with valeraldehyde, formaldehyde and ammonia over modified ZSM-5 (SiO₂/Al₂O₃=30) catalysts at 400 °C. High conversion (>90%) and high yield (72%) were obtained over PbZSM-5(30). The activity was correlated with the acidity of the catalyst. The modified catalysts were characterized by XRD, FT-IR, ICP-MS, BET-surface area and temperature programmed desorption (TPD) of NH₃.     

Synthesis of dodecylbenzene via the alkylation of benzene and 1-dodecene over mesopore Beta zeolites

The alkylation of benzene with long chain α-olefins is a crucial process in the production of fine chemicals, which requires the upgrading from traditional homogeneous catalysis to heterogeneous catalysis involving zeolites. However, the application of zeolite catalysts has been limited by their fast deactivation due to constrained diffusion resulting from the sole micropores. To address this challenge, a desilication and secondary-crystallization strategy has been employed to fabricate hierarchically structured mesoporous Beta zeolites. The resultant mesoporous Beta zeolites demonstrate excellent catalytic activity and stability in the alkylation of benzene with 1-dodecene, arising from the exposed acid sites and enhanced internal diffusion. Importantly, the internal diffusion limitations for these mesopore Beta zeolites are negligible, which significantly extends their lifetime and improves their regeneration performance. To achieve these benefits, the degree of mesopores must be deliberately controlled. Overall, this approach provides a promising solution for achieving efficient and environmentally friendly alkylation processes.     

Dimerization of isobutene over nickel modified zeolites to obtain isooctene

Ni/H Zeolites catalysts were prepared by impregnation, starting from HY-Zeolite, Hβ-Zeolite and H-mordenite with nickel precursor salts, NiCl₂, NiSO₄ and NiCO₃. The total number, NTSA, and the acid strength were found dependent on the nickel precursor salt. High catalytic activity, selectivity and stability of the modified zeolites in isobutene dimerization was attributed to the acidic properties of nickel modified zeolites. HY-Zeolite modified with NiCO₃ resulted more active and selective to dimerization reaction. The prepared catalysts were characterized by EDSX, SEM, and Adsorption/Desorption of N₂ at 77 K, NH₃ chemisorption and Ammonia Temperature-Programmed-Desorption (NH₃-TPD) and FT-IR of adsorbed pyridine. NH₃-TPD and isobutene adsorption revealed an acid sites a new distribution and apparition of acid sites not present in the protonated zeolites. Catalytic activity and reactor behavior were studied in a continuous downstream fixed bed reactor at 298 K, 27.6 kPa (4 psig), and WHSV = 0.27 h⁻¹.     

多级孔分子筛对四氢萘加氢生产轻质芳烃的影响

以多级孔Y分子筛为酸性组分,四硫代钼酸铵为金属前驱物,采用孔饱和浸渍法制备预硫化型催化剂,采用XRD、BET、TEM、NH3-TPD和Py-IR等分析方法表征分子筛结构性质。以四氢萘为模型化合物,在高压加氢微反装置上考察多级孔Y分子筛对四氢萘选择性加氢裂化性能的影响。结果表明,与参比分子筛相比,介孔比例高、介孔孔径尺寸适宜、介孔集中度高和酸性适中的多级孔Y型分子筛能够强化四氢萘转化及提高C_6~C_(10)和C_6~C_8单环芳烃收率;介孔孔径尺寸过大或介孔集中度低会提高重产物收率。实验条件下,C_6~C_(10)和C_6~C_8单环芳烃收率分别可达41.5%和24.0%。     

Benzene alkylation with methanol over phosphate modified hierarchical porous ZSM-5 with tailored acidity

The acidity and acid distribution of hierarchical porous ZSM-5 were tailored via phosphate modification.The catalytic results showed that both benzene conversion and selectivity of toluene and xylene increased with the presence of appropriate amount of phosphorus.Meanwhile,side reactions such as methanol to olefins related with the formation of by-product ethylbenzene formation and isomerization of xylene to meta-xylene were suppressed efficiently.The acid strength and sites amount of Br(o)nsted acid of the catalyst were crucial for improving benzene conversion and yield of xylene,whereas passivation of external surface acid sites played an important role in breaking thermodynamic equilibrium distribution of xylene isomers.     

Catalytic combustion of hexane over transition metal modified zeolites NaX and CaA

Hexane deep oxidation was studied over NaX and CaA zeolites modified by ion exchange with transition metals (Mn²⁺, Co²⁺, Fe³⁺), the percentage of ion exchanged, determined by ICP-MS, varying between 39 and 98%. Parent and exchanged zeolites were characterized by X-ray diffraction (XRD), N₂ physisorption, temperature-programmed reduction (TPR), oxygen and ammonia temperature-programmed desorption (TPD) and inverse gas chromatography (IGC). Catalytic activities were evaluated through the recording of light-off curves in a pulsed microreactor, catalytic activity being correlated with physicochemical properties of the solids (crystallinity, surface acidity, adsorption properties and morphological parameters). As general trend, CaA zeolites are more active than NaX zeolites. Mn-exchanged CaA zeolite was the most active catalyst for hexane oxidation, whereas the addition of Fe to the zeolites leads to strong chemical and morphological changes in the parent zeolite.