On the Effect of the M3+ Origin on the Properties and Aldol Condensation Performance of MgM3+ Hydrotalcites and Mixed Oxides

Abstract

Hydrotalcites (HTCs) are promising solid base catalysts to produce advanced biofuels by aldol condensation. Their main potential lies in the tunability of their acid-base properties by varying their composition. However, the relationship between the composition of hydrotalcites, their basicity, and their catalytic performance has not yet been fully revealed. Here, we investigate systematically the preparation of HTCs with the general formula of Mg6M3+2(OH)16CO3·4H2O, where M3+ stands for Al, Ga, Fe, and In, while keeping the Mg/M3+ equal to 3. We use an array of analytical methods including XRD, N2 physisorption, CO2-TPD, TGA-MS, FTIR-ATR, and SEM to assess changes in the properties and concluded that the nature of M3+ affected the HTC crystallinity. We show that the basicity of the HTC-derived mixed oxides decreased with the increase in atomic weight of M3+, which was reflected by decreased furfural conversion in its aldol condensation with acetone. We demonstrate that all MgM3+ mixed oxides can be fully rehydrated, which boosted their activity in aldol condensation. Taking all characterization results together, we conclude that the catalytic performance of the rehydrated HTCs is determined by the “host” MgO component, rather than the nature of M3+.

Chemical valorisation of biomass derived furanics and carboxylic acids over niobium-based catalysts

“…13 In the search for improved solutions and efficient catalysts to enhance productivity, different catalytic approaches have been reported to produce condensation products from Fur/acetone using acid, base or acid-base catalysts. 8,14 The C8 and C13 products were produced using solid base catalysts, most of which possessed magnesium, such as for C8, Mg-containing metal oxides, [15][16][17][18][19][20][21][22] hydrotalcites (HTs) or layered double hydroxides (LDHs), 14,23,[24][25][26][27][28][29][30][31]32,33 carbons, 34,35 and mineral meixnerite; 14 and for C13, metal oxides [36][37][38][39] and carbons. 40 In general, the reported Mg-containing catalysts were effective for the condensation reactions, but several studies reported the occurrence of catalyst deactivation 18,27,28,34,36 or did not report catalyst recyclability, 14,23,25,30,41 which represents an important knowledge gap because catalyst stability is fundamental in the development of sustainable heterogeneous catalytic processes.…”

Green Synthesis of 3-Hydroxybutyraldehyde from Acetaldehyde Catalyzed by La-Ca-Modified MgO/Al2O3

“…Some researchers have also adopted the multi-phase catalytic method of AcH condensation, but the reaction temperature is relatively high (mostly above 100 • C), resulting in the continuous reaction of 3-HBA of the unstable structure, producing 2-butenal [10,[13][14][15][16]. At the same time, the purification of 3-HBA among nonrecyclable catalysts and unreacted AcH is also a tough challenge [12,17]. More recently, it was found that basic ionic liquids were active for the aldol condensation reaction, which can achieve a higher total yield (75%) than NaOH (69%), while it is time-consuming and expensive [18].…”