Hirofumi Itoh

Measurement of the acidity of various zeolites by temperature-programmed desorption of ammonia

The acidity of H-form zeolites which include mordenite, ZSM-5, Y-faujasite, and those modified by cation exchange or dealumination was measured by temperature-programmed desorption (TPD) of NH3. Ammonia was adsorbed at 373 K to eliminate the contribution of very weak acid sites and improve the spectrum resolution. TPD spectra of mordenites and ZSM-5 zeolites had two desorption peaks named l and h with peak maximum at around 420 and 680 K, respectively, while the spectra of Y-zeolites had a broad peak. From the peak maximum temperature of h-peak, the acid strength was found to be in the order of HM > HZSM-5 > HY. Acid amount was evaluated from the desorption amount of NH3, and correlated with the infrared intensity of the OH band at 3600 cm−1 and the ammonium band at 1447 cm−1, thus indicating that the amount as well as distribution of strength of Bronsted acid sites can be measured by the present method. Cation exchange poisoned the strong acid sites preferentially, whereas dealumination reduced the acid sites in the whole region.

Mechanism of the side-chain alkylation of toluene with methanol

Abstract The side-chain alkylation of toluene with methanol has been studied experimentally and a detailed mechanism of the reaction has been investigated by using quantum chemistry. Experimental results have shown that this reaction proceeds consecutively; styrene is primarily formed by the reaction of toluene with formaldehyde produced by the dehydrogenation of methanol, followed by the hydrogenation of styrene to form ethylbenzene. The quantum chemical calculations have shown that the presence of a basic site is indispensable to the side-chain alkylation of toluene, whereas the benzene-ring alkylation of toluene takes place on an acidic site, in accordance with experiments. Furthermore, the calculations have indicated that specific configurations of acidic and basic sites with steric restrictions are required for the side-chain alkylation of toluene. This might explain the experimental results that alkali-cation-exchanged X and Y zeolites exhibit a higher activity for this alkylation compared to the other catalysts employed.

Role of acid and base sites in the side-chain alkylation of alkylbenzenes with methanol on two-ion-exchanged zeolites

Abstract The role of acid and base sites in the side-chain alkylation has been investigated using p-xylene as alkylbenzene on single- and two-ion-exchanged zeolites. Rb and Li two-ion-exchanged X type zeolites with the Li Rb + Li ratio of about 0.1 showed a higher activity than RbX and KX which showed the highest activity in single-ion-exchanged zeolites. RbX with a small amount of Li ion has slightly stronger acid sites than RbX, as measured by the temperature-programmed desorption (TPD) of ammonia and the Hammett indicators. Two cations in a zeolite are considered to form different active sites, such as acid and base sites, under their mutual effect. It is concluded that the active center which is the assemblage of acid and base sites with cooperative action is necessary in the side-chain alkylation of alkylbenzenes with methanol.

Role of acid property of various zeolites in the methanol conversion to hydrocarbons

The results of a study to detail the correlation between the catalytic performance in the methanol conversion and the acidity of zeolites are reported. The acid property was measured by the temperature-programmed desorption of NH/sub 3/. The extent of the reactivity of the zeolites is controlled by the acidity. The product distribution was well correlated with the amount of strong acid sites. As the strong acid sites decreased, C/sub 4//sup -/ paraffin, ethylene, and aromatics increased, while C/sub 5//sup +/ aliphatics and propylene and butene decreased.

Product distribution in the conversion of methanol on partially ion-exchanged mordenites

Abstract The conversion of methanol to hydrocarbons over ion-exchanged mordenites was investigated by a pulse reaction technique. The change in the activity and selectivity of mordenites as reaction conditions were varied was similar to that of ZSM-5 zeolite. Bro¨nsted acidity was measured from the intensity of the 1447 cm−1 IR band of adsorbed ammonia. Product distribution and Bro¨nsted acidity depended on the nature and extent of cation exchange. The decrease of Bro¨nsted acidity results in increase in olefin and aromatic yields and in decrease in coke deposit. The deposition of coke, moreover, depends on the strength of Bro¨nsted acid sites. In the reaction pathway, the important and reactive intermediates are the C3 and C4 species. A7 and A8 aromatics are alkylated to higher polyraethylbenzenes. The carbonaceous deposit is mainly formed from the polymethylbenzenes at strong and/or numerous Bro¨nsted acid sites.

Modification of H-mordenite by a vapour-phase deposition method

Depositing Si(Ome)4 from the vapour phase onto H-mordenite reduces the size of pore exits in the zeolite but leaves the acid sites unaltered.

Reduction of higher polymethylbenzenes by the rapid cation exchange of H-mordenite in the conversion of methanol to hydrocarbons

The product distribution in methanol conversion on mordenite is changed by potassium ion exchange depending on the method of ion exchange. The rapid exchange method was the most effective to suppress the formation of higher polymethylbenzenes.AbstractПод влиянием ионообмена калия распределение продуктов превращений метанола на мордените измеияется в зависимости от метола ионообнмена. Метод быстрого ионообмена оказался наиболе эффективным в подавлении образования более высоких полиметилбензолов.

Selective formation of alkenes in the conversion of methanol into hydrocarbons on barium ion-exchanged mordenite

C2–C4 alkenes were formed with more than 80% selectivity in the conversion of methanol into hydro-carbons over Ba ion-exchanged mordenite.

Change of Product Distribution in the Conversion of Methanol to Hydrocarbons with Cations in Mordenite

It has been known that methanol is converted to hydrocarbons over various zeolites, such as NaX [1], REX, ZnX [2], HM [3], and Ni, Cr and Pb exchanged CaY [4]. Since a new and simple catalytic process for the conversion of methanol to gasoline was recently reported by Mobil [5], this process has been widely investigated. If the product distribution can be controlled, the process will be more important. The product distribution may depend on the following two factors: the pore structure and the exchanged cation of zeolites. However, few works have been devoted to the systematic study of the effect ofcation exchange on this reaction. In this communication, the effect of cation exchange on the product distribution will be described. Alkali cation-, Caand La-exchanged mordenites were prepared by the following methods: H-mordenite (Norton Company Zeolon 100) was used as the starting material for all catalysts. HM was partially ion-exchanged with