Metathesis of Propene on Molybdenum−Alumina-Pillared Montmorillonite

Abstract

The preparation, characterization, and catalytic activity of molybdenum-alumina-pillared clays for the metathesis of propene were studied. Two solutions containing molybdenum and aluminum were used in the preparation of the intercalation solutions. In the first, a mixed hydroxy-aluminum-molybdenum solution (MoAl) was prepared by slow addition of NaOH to a solution of mixtures (AlCl 3 and MoCl 5 ). The second solution (Mo + Al) was obtained by dissolving MoCl 5 in an aged solution of aluminum polycation. These solutions were used to prepare two molybdenum-alumina-pillared clays. Finally, an alumina-pillared clay (AlPILC) was used as support and impregnated with a molybdenum solution. Nitrogen adsorption data obtained from very low relative pressures were used for the characterization of the microporosity of the solids. The Dubinin-Radushkevich formalism was used to describe the volume filling of micropores and confirmed the existence of a bimodal distribution of the micropore sizes in the pillared clays. The micropore distributions obtained by the Horvath-Kawazoe approach for the two molybdenum-alumina-pillared clays showed a modification of their microporous surface with respect to the AlPILC. The acidity and catalytic activity in the propene metathesis reaction of the molybdenum-alumina-pillared clays and a comparison with two reference catalysts (Mo/ SiO 2 and Mo/Al 2 O 3 ) are also reported.

Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce and La

“…To analyze the microporosity of the pillared clays, nitrogen adsorption over a pressure range is required (Gil and Montes, 1997) and this is given by DubininRadushkevich plots [log V versus log2(P0/P)] for F bentonite and the derived pillared clays (Figure 3). The untreated F bentonite (Figure 3) showed a near unimodal distribution of micropore sizes.…”

“…These materials have been used in isomerization and dehydrogenation reactions: A1-Ga (Viera Coelho and Poncelet, 1991), A1-Zr (Occelli, 1986), A1-Fe (Oades, 1984;Lee et al, 1989;Bergaya et al, 1993), and A1-Cr (Lee et al, 1989). Another possible method to obtain pillared clays with mixed-oxide pillars is to use transition-metal ions by impregnation (Gil and Montes, 1997), with the pillared clay acting as a substrate. Pillared clays have been prepared also by cation exchange, either before or after initial pillaring of the clay (Suzuki et al, 1988;Carrado et al, 1986).…”

Molybdenum modified Montmonrillonite clay as an efficient catalyst for low temperature NH3‐SCR

“…It was acknowledged that the peak between 100–400 °C was mainly ascribed to the NH 3 desorption from weak and medium Lewis and Brønsted acid sites, while peaks above 300 °C usually were attributed to Brønsted acid sites . Brønsted acid sites were coming from the –OH groups on the clays layers, whilst the Lewis acid sites usually came from the intercalated metal oxides, hence the Brønsted acid sites were less thermally stable . The load of Mo resulted in an increase of surface concentration of chemisorbed ammonia from 176 to 321 μmol·g −1 , indicating higher acidity.…”

“…5,22 Brønsted acid sites were coming from the -OH groups on the clays layers, whilst the Lewis acid sites usually came from the intercalated metal oxides, hence the Brønsted acid sites were less thermally stable. 17,56 The load of Mo resulted in an increase of surface concentration of chemisorbed ammonia from 176 to 321 μmol·g −1 , indicating higher acidity.…”