Alkali-free Media Research Articles

Organic Acid Anions Modified α-Co(OH)2 with Enhanced Activity for the Decomposition of Cyclohexyl Hydroperoxide

α-Co(OH)2 nanoplatelets with tunable wettability (hydrophilicity/hydrophobicity) and interlayer spacing were designed to catalyze cyclohexyl hydroperoxide (CHHP) decomposition in alkali-free medium...

Low-temperature synthesis, structure, sorption properties and acidity of zeolite ZSM-5

High structure-directing activity and specificity of templating action of tetrapropylammonium cations TPA+ as well as high concentration of framework-forming substances in the initial reaction mixtures contribute to the formation of zeolite ZSM-5 at relatively low temperature (100 °C) in the alkali-free media. Zeolite ZSM-5 obtained at 100 °C has higher micropore and mesopore volumes, specific surface area, less uniform micropore size distribution in comparison with ZSM-5 synthesized at 170 °C in an alkaline medium in the presence of hydrated Na+ cations. Samples synthesized at 100 °C possess a lower concentration of acid sites and broader distribution of them in strength, compared with ZSM-5 obtained at 170 °C in an alkaline medium. ZSM-5 obtained at 100 °C exhibits a high catalytic activity in the reaction of cracking of cumene, as well as a higher selectivity to propylene and styrene, in comparison with isostructural analogue obtained at 170 °C in an alkaline medium. It is assumed that the investigated alkali-free reaction mixtures and the corresponding sol-precursors of zeolite ZSM-5 containing the elements of secondary building units can be used for obtaining of micro-mesoporous aluminosilicates in the conditions of low-temperature synthesis (100 °C) by dual-template method—in the presence of molecular and micellar templates.

Selective decomposition of cyclohexyl hydroperoxide by copper ion-containing quaternary ammonium salts in alkali-free medium

Abstract A novel catalytic system composed of quaternary ammonium salts and copper (II) chloride was prepared. The catalyst showed high conversion and selectivity in the decomposition of cyclohexyl hydroperoxide to cyclohexanol and cyclohexanone (K/A oil) at room temperature in alkali-free medium. 93% conversion with 96% selectivity for cyclohexanone and cyclohexanol could be obtained.

A new way to obtain acid or bifunctional catalysts. III. Steaming of as-synthesized TPA, MeNH 3-[Ga,Al]-ZSM-5 zeolites obtained from alkali-free media

The steaming of as-synthesized alkali-free TPA-MeNH 3-[Ga 0.99Al 1.99]-ZSM-5 zeolite was carried out at temperatures of 530°C (St-530), 550°C (St-550), and 600°C (St-600). Physical characterization of the solids was carried out by XRD, IR, N 2 adsorption, and 27Al and 71Ga MAS-NMR. n-Heptane cracking ( T=350°C; P N 2 / P nC 7 =4; P=1 atm) was used as a model reaction to characterize the acidity of the catalysts. Propane aromatization ( T=530°C; P=1 atm) was used to characterize the acid or the bifunctional behavior of solids. Results show that steaming produces less acid solids due to degalliation and dealumination of the zeolite structure. Because the presence of steam reduces the temperature at which the formation of extra framework gallium species occurs, bifunctional “Ga 2O 3”/H-[Ga,Al]-ZSM-5 catalysts are formed at lower temperature ( T=530°C) in comparison when calcination is carried out under dry air. Catalysts are less selective to BTX as steaming temperature increases because of a strong reduction of Bronsted acid sites.

A new way to obtain acid or bifunctional catalysts. II. Straightforward calcination of as-synthesized [Ga,A1]-ZSM-5 zeolites obtained from alkali-free media

The acid or bifunctional behavior of catalysts obtained by the straightforward calcination (530–800°C) of as-synthesized [GaA1]-ZSM-5 zeolite, obtained from alkali-free media, was determined using propane, cyclohexane and cyclohexene transformations ( T = 530°C, p = 1 atm) as reaction models. Solids were characterized by XRD, FTIR, N 2 adsorption, 27A1 and 71Ga MAS NMR and chemical analysis. The catalyst acidities were evaluated using n-heptane cracking and m-xylene isomerization as reaction models. Results show that calcination temperatures (T c)between 530 and 550°C, causes only the removal of organic molecules used for the synthesis of the zeolite, leading then to pure acidic catalysts. At 700 ⩽ T c ⩽ 800°C, simultaneously with the removal of those organic molecules, a significant chemical change of the zeolite framework composition take place (degalliation and dealumination). The presence of extraframework gallium species (EFGS), led to acid gallium promoted bifunctional catalysts with catalytic properties for propane and naphthenes aromatization almost identical to those for gallium promoted zeolites obtained by conventional methods (ion exchange and/or impregnation).

Preparation of acidic or bifunctional catalysts by means of straightforward calcination of as-synthesized [Ga]-ZSM-5 zeolites obtained from alkali-free media. Propane aromatization

Propane aromatization (530°C, 1 atm) was used as a reaction model to evaluate the effect of the calcination temperature on the catalytic properties of an as-synthesized [Ga1.3]-ZSM-5 zeolite obtained from alkali-free media and calcined at two different temperatures: 530°C (C-530) and 750°C (C-750). Results show that in spite of its lower acidity, C-750 is more active and selective toward aromatics than C-530. This is probably due to the fact that at higher temperature the decomposition of organic compounds used during the zeolite synthesis is accompanied by a partial degalliation of the zeolitic support leading to the production of a bifunctional x“Ga2O3” /H-[Gay-ZSM-5(2x+y=1.3)catalyst.