Selective liquid-phase bromination of toluene catalysed by zeolites

The liquid-phase bromination of toluene catalysed by zeolites has been investigated. Different types of zeolites as well as several cation-exchanged Y-type zeolites have been used. The initial rates are increased in comparison to the uncatalysed or Lewis acid-catalysed reaction. With some zeolites, the para/ortho isomer ratio could be increased.     

Hydroesterification of bio-oils over HZSM-5, BETA and Y zeolites

The primary aim of this research is to study the influence of various experimental parameters on the reaction in order to establish the optimum conditions for which the highest conversion level of zeolite-catalysed oil hydroesterification (two-step reaction: oil hydrolysis and fatty acid esterification) can be achieved. The experimental results indicate that optimising the reaction temperature and stirring rate (providing adequate mass transfer rate and preventing the diffusion limitations) are the main factors to reach into the optimal catalytic performance. An inadequate concentration of water and alcohol can lead to incomplete conversion of the oil during the hydrolysis and fatty acid esterification steps. Exceeding stoichiometric values during hydrolysis (excess H₂O) or esterification (excess CH₃OH) does not enhance the conversion level of the oil and can act adversely on the extent of hydroesterification. In excess of 95% of the original zeolite activity was recovered via calcination in air during studies of catalyst deactivation.     

Conversion of toluene and trimethylbenzene over NaHY zeolites

The conversion of toluene, 1,2,4-trimethylbenzene (TMB), and other C₉ aromatics on NaHY zeolites was investigated in a fixed-bed, continuous flow reactor at 460°C and a pulse microreactor at 400°C. It was found that the product distribution and reaction selectivity are dependent on the alkali-ion content in NaHY and the composition of feedstocks. Disproportionation was the main reaction in the conversion of toluene or TMB. In the reaction of toluene with 1,2,4-TMB, the amount of xylene produced from TMB dealkylation and TMB-toluene transalkylation was greater than that from toluene disproportionation; in turn, the product xylene to benzene mole ratio was found to be 7–27. The selectivity of TMB dealkylation increased with increasing Na⁺ content in NaHY or increasing 1,2,4-TMB concentration in feed. Among all the C₉ aromatics studied, the reaction of toluene with TMB produced the greatest amount of xylene.     

Monte Carlo simulation of alkylation of toluene with alcohols over zeolite catalysts

A Monte Carlo model for the simulation of alkylation of toluene with alcohols over zeolite catalysts was developed. On the basis of the experimentally observed parameters, including the intracrystalline diffusivity, equilibrium adsorption constant, and intrinsic rate constant, the alkylations of toluene with methanol and ethanol were simulated. The results were in good agreement with those of the experiments. This suggests that the Monte Carlo method is helpful for investigating the nature of shape selectivity in zeolite-catalyzed reactions.     

Alkylation of toluene with methanol on zeolites. The role of electronegativity on the chain or ring alkylation

Catalysed alkylation of toluene with methanol on zeolites proceeds in two different ways, depending upon the nature of the zeolite, and gives rise to ethylbenzene-styrene and/or xylenes. The results indicate that the activity and selectivities are dictated by the acidity and electronegativity of the zeolites with the most electropositive ones producing ethylbenzene and styrene and the most electronegative catalysing formation of xylenes.     

HZSM-5-catalyzed shape-selective formation of diacetates

This paper describes the preparation of diacetates from aromatic and aliphatic aldehydes and acetic anhydride under ambient conditions using HZSM-5 catalyst. The initial rate and overall yield are less with ortho-substituted than with para-substituted aromatic aldehydes, indicating shape selectivity. Also, rates are very low with cyclohexyl and 2-ethylhexyl aldehydes when compared with n-hexyl, indicating that the reaction is controlled by the size of the molecule. Sizes of the aldehydes and their corresponding diacetates were estimated by molecular modeling and graphics technique and were compared with the size of the zeolite cage. The initial rate of reaction was a function of the size of the aldehydes and their corresponding diacetates, as estimated by the modeling technique.     

On the unusual mechanism of Lewis acidity manifestation in HZSM-5 zeolites

The adsorption of CD₃CN and NH₃ on HZSM-5 zeolites containing prechemisorbed olefins were studied using diffuse reflectance i.r. spectroscopy. It is shown that in the presence of strong bases the unusual manifestation of Lewis acidity in these zeolites takes place as a result of fission of the Al←O bond in bridged alkoxyl groups by adsorbed base molecules. Nonempirical quantum-chemical calculations confirm this experimental finding and define the requirements of such Lewis acidity generation.     

A novel electrochemical alkylation of aniline with methanol over Zn/Cu salts modified kaolin

A novel liquid phase alkylation of aniline with methanol over Zn/Cu salts modified kaolin assisted with a pair of porous carbon electrode in slurry-bed reactor under constant current intensity, room temperature and atmospheric pressure was reported. The Zn/Cu salts modified kaolin catalysts were synthesized and characterized by infrared spectrometer (IR), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), which showed that the transition metals were completely supported on kaolin's structure and formed a pored one. The effect parameters, such as initial pH, electrolysis time, metal ratio with kaolin and salts composition in this electrochemical catalytic system, were studied. The procedure was inspected by ultraviolet-visible spectrum (UV-vis), and the product distribution was detected by gas chromatography/mass spectrometry (GC/MS). In addition, a possible reaction mechanism was also proposed.     

盐酸改性V_2O_5/TiO_2及其催化甲醇选择性氧化的研究

对TiO2负载V2O5催化剂进行盐酸改性制得了HC-V/TiO2催化剂,并将其应用于甲醇选择性氧化制二甲氧基甲烷(DMM)。V2O5负载量为10%的催化剂10V/TiO2上,钒氧物种具有良好的分散性。对10V/TiO2进行不同量的盐酸改性制备了HC-10V/TiO2催化剂,对其进行XRD、UV-Vis、H2-TPR、NH3-TPD表征。结果表明,适量的盐酸改性能有效改善催化剂的酸性,但对钒氧物种的分散性和还原性没有影响,改性后催化剂的反应活性和稳定性也得到很大提高,甲醇转化率和DMM选择性明显增加。Cl-负载量为4%的催化剂4HC-10V/TiO2在反应温度160℃时,甲醇的转化率为77.60%,DMM的选择性高达78.31%。     

Reactions of alcohols with hydrogen sulfide over zeolites: IV. The role of acidity in the hydrosulfurization of ethanol over X-type zeolite catalysts

The reaction of ethanol with hydrogen sulfide was studied on divalent cation-exchanged X-type zeolites at 523 K. The decomposition of ethanol to hydrocarbons is competitive with the hydrosulfurization process, i.e., the reaction between EtOH and H₂S. Brönsted acid sites together with divalent cations are involved in the hydrosulfurization of ethanol. Cation sites take part in the formation of ethanethiol. The increase of the strength of Brönsted acid sites causes the increase of the selectivity towards diethyl sulfide.     

Methanol conversion to hydrocarbons over WO3/HZSM-5 catalysts prepared by metal oxide vapor synthesis

Metal oxide vapor synthesis (MOVS) methodology was used to deposit WO₃ on the zeolite HZSM-5. Samples I, II, and III of various weight percentage-loaded (3.1, 5.4, and 10.8, respectively) WO₃ on the HZSM-5 support were prepared. These materials were characterized by powder X-ray diffraction pattern, sorption, chemical analysis, and scanning electron microscopy. The characterization studies showed good crystalline nature of the support, partial inclusion of WO₃ particles into the zeolite cavities, and a uniform deposition of amorphous WO₃ over the support. These samples were tested for their catalytic activity in the conversion of methanol into hydrocarbons. Results were compared with that of pure support under identical conditions. The product selectivity for aromatics over WO₃/HZSM-5 catalyst samples was negligible compared with the same selectivity observed over pure support, whereas the selectivity for olefins increased significantly.     

Mixture effects during the oxidation of toluene, ethyl acetate and ethanol over a cryptomelane catalyst

The catalytic oxidation of two-component VOC mixtures (ethanol, ethyl acetate and toluene) was studied over cryptomelane. Remarkable mixture effects were observed on the activity and the selectivity. Toluene inhibits both ethyl acetate and ethanol oxidation, this effect being more evident in the case of ethyl acetate. For instance, the temperature for 100% conversion is about 210 °C when ethyl acetate is oxidised alone, and 250 °C or higher, when it is oxidised in mixtures with toluene. On the contrary, toluene oxidation is only slightly inhibited by the presence of ethyl acetate, while the presence of ethanol has a promoting effect. Concerning the mixtures of ethyl acetate and ethanol, both compounds have a mutual inhibitory effect, which is more evident in the case of ethyl acetate (the temperature for 100% conversion of ethyl acetate is about 45 °C higher when ethyl acetate is oxidised in mixtures with ethanol, while in the case of ethanol the corresponding increase is only 10 °C).