Acid–Base Promoted Dehydrogenation Coupling of Ethanol on Supported Ag Particles

Abstract

Dehydrogenation coupling of ethanol to n-butanol has received much attention due to the wide application of n-butanol. Highly selective butanol production from ethanol remains a challenge due to competitive reactions in the dehydrogenation and/or condensation and great difficulty in ethanol dehydrogenation. This work reports a synergistic catalysis between layered double hydroxide (LDO), an acidic−basic support, and supported Ag particles for the dehydrogenation coupling of ethanol to n-butanol. A selectivity of up to 77% toward n-butanol with an ethanol conversion of 23.2%, among impressive levels reported till now, has been achieved at 350 °C, 0.1 MPa. A selectivity of up to 60% toward nbutanol with an ethanol conversion of 45%, the highest selectivity at an ethanol conversion of >45% reported till now, has been achieved at 250 °C, 2 MPa. A synergistic catalysis between the acid−base sites of the LDO surface and supported Ag particles have been revealed to contribute the excellent butanol selectivity: basic sites promote adsorption and subsequent dehydrogenation of ethanol on Ag particles; in addition to the promotion from Ag, the following aldol condensation is boosted by acid−base cooperation.

Ethanol Dehydrogenation: A Reaction Path Study by Means of Temporal Analysis of Products

“…Recently, basic research into new catalysts for the synthesis of higher alcohols on a renewable basis via aldolic condensation has been gaining increasing attention [1][2][3][4][5][6]. Amongst these alcohols, iso-butanol in particular has been identified as very promising from various perspectives.…”

Bio-DEE Synthesis and Dehydrogenation Coupling of Bio-Ethanol to Bio-Butanol over Multicomponent Mixed Metal Oxide Catalysts

“…Most likely, for studied WP-X catalysts, both H 2 and produced H 2 O can act as hydrogen donors, as suggested earlier [73]. In the second mechanism, i.e., direct condensation, the first activation of the β-H of ethanol molecule is followed by the condensation with another ethanol via dehydration [74]. Thus, dual functionality of catalytic systems is required to provide desirable Guerbet conversion and selectivity, where one component is active in ethanol dehydrogenation and support or/and the second component shapes the acetaldehyde aldolization selectivity.…”

“…In the Guerbet reaction, the C-C formation occurs via aldol condensation. This reaction includes dehydrogenation of ethanol to an aldehyde (often identified as the rate-limiting step), followed by aldol-type condensation of aldehyde and transfer hydrogenation (TH) of polarized substrates [73,74]. Most likely, for studied WP-X catalysts, both H 2 and produced H 2 O can act as hydrogen donors, as suggested earlier [73].…”

Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol

“…Zhang et al used a Mg x Al-LDO (layered double hydroxide) with ratios of Mg to Al ranging from 1 to 4 loaded with 8 nm Ag-particles, in which the density of the basic sites was much higher compared to the Cu/MgAl catalyst described above. With an acid base site ratio of 0.41, the conversion and selectivity towards n-butanol was optimal in the case of this support [9]. Other supports, such as hydroxyapatite, were also used and the ratios of Ca/P and Sr/P were investigated in order to identify an optimal acid base site ratio [10,11].…”