Abstract

Baber Masood Bhat

Previous Studies on MgO doped by alkali cations have shown that solid catalyst are efficient for the aldolization, because of having preferably a high concentration of surface basic hydroxyl groups. Indeed the Mg-Al hydrotalcites actuvated by calcinations at temperatures not exceeding 1073K are mixed oxides of Mg(Al)O type. They show the structure of MgO with smaller crystallographic parameters, then in periclase (MgO). The decrease of the size of the unit cell with increasing Al content can be accounted for by the smaller ionic size of Al³⁺(0.050 nm), then Mg²⁺(0.060 nm). These mixed oxides contain both basic sites identified to O²⁻ and OH- in amounts depending upon the calcinations temperature, i.e., is of the dehydroxylation degree of the hydrotalcite and Lewis acid sites provided by Al³⁺ and Mg². The existence of acid-base pairs justifies the catalytic properties of hydrotalcites for the Aldolisation. The synthesized Hydrotalcites were then characterized using XRD and TGA/DTA techniques, which confirmed that the synthesized materials are hydrotalcite like compounds. There after the synthesized Hydrotalcites were successfully applied for the typical Aldol Condensation reaction of propionaldehyde and formaldehyde to get desired product methacrolein. We tested catalytic activity of synthesized hyrotalcites and from the results it was clear that, the Mg - Al hydrotalcite catalyzed Aldol reaction propionaldehyde coversion of 57.78% and with selectivity 51.23%to methacrolein. Ni- Al hydrotalcite showed a propionaldehyde conversion of 53.46%with 35.46% selectivity. Co – Al XRD pattern of the formed material confirms that the material is not hydrotalcite like. This material also did not show any catalytic activity for the above said Aldol condensation reaction.

Aldolization; Hydrotalcites; Propionaldehyde conversion

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