A hydrotalcite-based catalyst system for the single-stage liquid-phase synthesis of MIBK

Abstract

A comparative study was performed between Pd supported on activated hydrotalcites bi-functional catalysts and physical mixtures of activated hydrotalcites with Pd supported on carbon nanofibers for the single-stage liquid-phase synthesis of methyl isobutyl ketone from acetone and H 2 . Since it was found earlier that the dehydration reaction of diacetone alcohol over activated hydrotalcites is the rate-determining step in this process, Mg-Al hydrotalcites were investigated in the condensation of acetone to diacetone alcohol and its dehydration to mesityl oxide to enhance the activity. A correlation between the number of active base sites, as determined by volumetric CO 2 adsorption measurements at low pressures, and the activity in the dehydration reaction could be derived. A dependency on the Pd-loading (0-1 wt%) of Pd supported on activated hydrotalcites catalysts was found in the single-stage synthesis of methyl isobutyl ketone, whereas no such an effect was found when using physical mixtures of activated hydrotalcites with Pd on carbon nanofibers. Results from TEM, CO 2 chemisorption and N 2 physisorption as well as catalytic experiments in the hydrogenation of mesityl oxide and of cyclohexene indicate that this dependency is largely accounted for by entrapment of Pd particles in the agglomerates of the irregular stacks of hydrotalcite platelets, making these sites inaccessible for the reactants. #

Exploring, Tuning, and Exploiting the Basicity of Hydrotalcites for Applications in Heterogeneous Catalysis

“…This reason was put forward to explain the higher activity obtained with liquidphase rehydrated hydrotalcites in the aldol condensation of citral and acetone: liquid-phase rehydration produced smaller particles with very thin platelets (Figure 7). [71] Knowing this, researchers have developed other methods to increase the irregularity of the stacked platelets and have observed dramatic increases in activity for the epoxidation of styrene, [76] self-condensation of acetone, [125,126] aldol condensation of acetone and citral [77] and so forth. In that sense, steric hindrance for the substrate molecules may also be a determining factor and thus the choice of a probe similar in size is crucial too.…”

Support and Size Effects of Activated Hydrotalcites for Precombustion CO2Capture

“…This results in positively charged layers, which are balanced by charge-compensating anions (e.g., Cl -, Br -, CO 3 ) located in the interlayer region, where hydrating water molecules are also accommodated. HTs have received considerable attention in recent years because of their wide range of applications, such as base catalysts, [30][31][32][33][34] ion exchangers, 35,36 polymer stabilizers, and drug targets. 37 The edges, and thus the lateral dimensions of the HTs, have a significant influence on their catalytic behavior.…”

“…This results in positively charged layers, which are balanced by charge-compensating anions (e.g., Cl − , Br − , CO 3 2− , I − , NO 3 − , OH − , SO 4 2− ) located in the interlayer region, where hydrating water molecules are also accommodated. HTs have received considerable attention in recent years because of their wide range of applications, such as base catalysts, − ion exchangers, , polymer stabilizers, and drug targets . The edges, and thus the lateral dimensions of the HTs, have a significant influence on their catalytic behavior. ,, Previous work from our group showed an increase in activity in base catalysis with decreasing platelet size for activated HTs (self-condensation of acetone).…”

Catalysts, Supported

“…As to the former, the combination of base with reducing centers plays an important role in minimizing the production of secondary amines (148)(149)(150).…”