Effect of Au nanoparticles on the activity of TiO 2 for ethanol upgrading reactions

Abstract

This article analyses the role of gold nanoparticles supported on TiO 2 for the gas-phase ethanol condensation. Previously, the original P25 surface was modified for increasing the Au-Ti interaction, in order to minimize the thermal deactivation. Catalysts were tested both in absence and presence of hydrogen (523-673 K, WHSV = 7.9 h-1 ; y EtOH = 0.32; y H2 = 0-0.1; 0.1 MPa). Parent TiO 2 is mainly selective for dehydration reactions yielding diethyl ether (favoured at low temperatures) and ethylene (favoured at higher temperatures). The presence of Au i n the catalyst promotes dehydrogenation pathways, yielding acetaldehyde, as well as condensation products (mainly butanol, with selectivities close to 10%). According to DRIFT spectroscopy results, the strong ethanol adsorption on the TiO 2 surface justifies the low yie lds and the high relevance of side-reactions produced by inter-or intra-molecular dehydration routes (diethyl ether, and ethylene formation). The gold addition minimizes this adsorption and enhances the main route by a double role: an improvement in the dehydrogenation rate (yielding more acetaldehyde) and an enhancement in the hydrogenation steps.

Tuning the selectivities of Mg-Al mixed oxides for ethanol upgrading reactions through the presence of transition metals

“…The second modification proposed in this work is to feed controlled amounts of hydrogen, in order to both, keep reduced these nanoparticles, and to improve their performance in hydrogenation steps. This idea is supported by our previous studies with Au/TiO for this reaction, obtaining an improvement of 74 % in the conversion and almost % in the 1-butanol selectivity when working in presence of H 2 [27].…”

Difference in the deactivation of Au catalysts during ethanol transformation when supported on ZnO and on TiO2

“…This has also been supported by literature where it is said that TiO 2 offers higher selectivity towards diethyl ether in comparison to other oxides due to the fact that the stronger interaction between the reactant and surface leads to preferential formation of this product by the reaction between two molecules of ethanol. 32 Likewise, in a previous study performed by our research group, acid and basic sites of ZnO materials were characterized by the isopropanol reaction test and conrmed that this material exposes mainly basic sites. This would explain the higher selectivity to the dehydrogenation product, acetaldehyde.…”

“…30,31 Very recently, J. Quesada et al analyzed the role of Au nanoparticles supported on TiO 2 in the ethanol condensation reaction obtaining improved results, when compared to the bare support, in particular as refers to dehydrogenation activities. 32 As was previously mentioned, when employed without incorporation of metal phase, metal oxides have also shown catalytic activity. For the partial oxidation of ethanol to acetaldehyde, TiO 2 gave highest activity results at lowest reaction temperature when compared with Al 2 O 3 , SBA-15 (mesoporous SiO 2 ) or hydrotalcite.…”

“…In the previously cited ref. 32, the presence of Au changes the selectivity pattern of the TiO 2 support due to its role promoting the ethanol dehydrogenation to acetaldehyde, and also favoring the hydrogen transfer step of aldol condensation product (view reaction scheme presented in Fig. 9) thereby resulting in the formation of C4 alcohols.…”

Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

“…We posit that catalysts that show high rates and selectivity in the butyraldehyde hydrogenation reactions will also show high rates and selectivity for the upgrading of ethanol to butanol and higher oxygenates; we have shown the efficacy of this approach in screening similar ABE condensation catalysts [19] . This assumption is based on the hydrogenation of aldehydes being the microscopic reverse of the dehydrogenation of alcohols, the rate-determining step of the Guerbet condensation [13,50]. In our experiments, the PdCu alloys acted as ethanol dehydrogenation catalysts, while TiO2 was used as a co-catalyst [9,19,51].…”