Effects of Alkali Metal Oxide Additives on Cu/SiO₂ Catalyst in the Dehydrogenation of Ethanol

Abstract

A series of Cu/SiO2 catalysts with various alkali metal oxide additives was investigated to elucidate the effects of additives on the catalytic properties of copper catalysts in the dehydrogenation of ethanol. The catalysts were prepared by the impregnation method and were characterized by X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption of CO2, and H2−N2O titration. The dehydrogenation reaction was carried out in a continuous-flow reactor at 300 °C under atmospheric pressure. The catalytic properties of the copper catalysts were strongly affected by the additives. The addition of alkali metal oxide increased the concentration of weak basic sites of the catalyst. The increase in turnover frequencies of the alkali-metal-oxide-modified catalysts was mainly due to the promotional effects of weak basic sites on Cu catalysts. KCu/SiO2 catalyst was very stable in the reaction process. The stabilities of NaCu/SiO2 and RbCu/SiO2 catalysts were similar to that of the unmodified catalyst. The decay of the catalysts during reaction was caused by sintering. The kinetics for deactivation can be described by a concentration-independent second-order expression.

Selective non-oxidative dehydrogenation of ethanol to acetaldehyde and hydrogen on highly dilute NiCu alloys

“…[5,6] Monometallic Cu-based catalysts are widely used for this reaction; however, quick deactivation of copper takes place, attributed to copper particle sintering. [4,7]. On the other hand, the oxidative dehydrogenation (ODH) of ethanol to acetaldehyde and water is the oldest laboratory method to produce acetaldehyde.…”

“…[13,14] On the other hand, as mentioned above, the catalytic activity of Cu has been found to decrease rapidly even in the first hour of the reaction, where the deactivation has been attributed to the sintering of metallic Cu at the high dehydrogenation temperature. [7,14] In searching for a promoter to inhibit the sintering of Cu, it has been reported that the incorporation of chromium oxide into Cu improves the catalyst stability. [13,15,16] However, the adverse environmental issues associated with the use of chromium have discouraged the application of this approach.…”

“…The addition of alkali metal oxides has also been reported to improve the stability of Cu, although the effect is less significant than chromium oxide. [7] Alternatively, the dehydrogenation of ethanol on Au NPs supported on reducible oxides has also been explored. [3,[17][18][19] Supported Au NPs with certain particle sizes have been demonstrated to have high activity and selectivity for the reaction.…”

“…lists the surface areas (per gram of Cu) of silica supported Ni 0.01 Cu NPs, np-Ni 0.01 Cu (SSM), and np-Ni 0.003 Cu (DL). The surface area of silica supported Ni 0.01 Cu NPs was calculatedbased on following equations, assuming the spherical shape of particles:[7,49] Cu is the specific surface area of Cu (m 2 /g), while d Cu stands for the average particle size of Cu (nm), here ~14 nm as determined from XRD and TEM. The surface areas of np-Ni 0.01 Cu (SSM) and np-Ni 0.003 Cu (DL) were determined from BET measurements, listed inTable 1.…”

Copper Supported on Hybrid C@SiO2 Hollow Submicron Spheres as Active Ethanol Dehydrogenation Catalyst

“…[10,11] Reducing the density of Si-OH over SiO 2 surface is an effective way of promoting selectivity, but simultaneously leading to instability. [12] Compared with SiO 2 , carbon materials possess relatively inert surface. [13] The Cu/C catalyst shows a substantially improved acetaldehyde selectivity by minimizing the secondary reactions.…”