Hydrotalcites: relation between structural features, basicity and activity in the Wittig reaction

The One‐Pot Wittig Reaction: A Facile Synthesis of α,β‐Unsaturated Esters and Nitriles by Using Nanocrystalline Magnesium Oxide

“…Sychev et al reported that hydrotalcites efficiently catalyzed the liquid phase synthesis of alkenes in the Wittig reaction, but they did not specify the reusability of the catalyst. [25] Yong Tong et al, reported soluble PEG-supported telluride as an effective catalyst for the Wittig-type reaction to give a variety of a,b-unsaturated esters. The catalyst was recovered quantitatively, but in the second run only a 69 % yield was obtained.…”

In situ growth of layered double hydroxide films on anodic aluminum oxide/aluminum and its catalytic feature in aldol condensation of acetone

“…One of the most interesting features of these materials is their role as catalysts or precursors for catalysts. On calcination of the LDHs with compensating carbonate anions at about 773 K and subsequent rehydration of the calcined LDHs (CLDHs) at room temperature, the activated rehydrated LDHs (RLDHs), which are similar to the mineral meixnerite possessing the original brucite-like layers but with compensating anions being hydroxide rather than carbonate (Braterman et al, 2004), have base catalytic activity and have been studied as solid catalysts for Claisen--Schmidt condensation (Climent et al, 2004), Knoevenagel condensation (Kantam et al, 1998), Wittig (Sychev et al, 2001), Henry (Choudary et al, 1999), Michael addition (Ebitani et al, 2006) and aldol condensation (Tichit et al, 1998;Prinetto et al, 2000;Roelofs et al, 2000Roelofs et al, , 2001Zhang et al, 2004;Abelló et al, 2005aAbelló et al, , 2005bWinter et al, 2005) reactions. However, use of powder catalysts on an industrial scale gives rise to a number of problems, such as high pressure drop and difficult catalyst separation.…”

Synthesis of Ce and Pr-promoted Ni and Co catalysts from hydrotalcite type precursors by reconstruction method

“…The promoted materials desorption display signals at temperatures higher than 400 C, which can be associated to strong basic sites. Some authors attribute these signals to dehydroxylation processes and the complexation of carbonate species on the metallic sites [4,46,47]. As well, Table 4 evidence that the promoted catalysts exhibit an increase in the proportion of the weak basic sites, suggesting that the physical-adsorption of CO 2 is promoted by Ce and Pr introduction [19].…”

“…This property is known as "memory effect" or reconstruction of the hydrotalcite phase [4]. The possibility of modifying the bi-and trivalent cations, their proportion, and/or the interlayer anions, presents the hydrotalcite type solids as versatile systems with better catalytic properties [1].…”