Evaluation of Au/ZrO2 Catalysts Prepared via Postsynthesis Methods in CO2 Hydrogenation to Methanol

Abstract

Au nanoparticles supported on ZrO2 enhance its surface acidic/basic properties to produce a high yield of methanol via the hydrogenation of CO2. Amorphous ZrO2-supported 0.5–1 wt.% Au catalysts were synthesized by two methods, namely deposition precipitation (DP) and impregnation (IMP), characterized by a variety of techniques, and evaluated in the process of CO2 hydrogenation to methanol. The DP-method catalysts were highly advantageous over the IMP-method catalyst. The DP method delivered samples with a large surface area, along with the control of the Au particle size. The strength and number of acidic and basic sites was enhanced on the catalyst surface. These surface changes attributed to the DP method greatly improved the catalytic activity when compared to the IMP method. The variations in the surface sites due to different preparation methods exhibited a huge impact on the formation of important intermediates (formate, dioxymethylene and methoxy) and their rapid hydrogenation to methanol via the formate route, as revealed by means of in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analysis. Finally, the rate of formation of methanol was enhanced by the increased synergy between the metal and the support.

Addressing the CO2 challenge through thermocatalytic hydrogenation to carbon monoxide, methanol and methane

“…The formate pathway was determined on an Au/ZrO 2 catalyst prepared by both impregnation and deposition precipitation. 211 A mixed oxide In 2 O 3 –ZrO 2 strongly enhanced the catalytic activities with respect to the Au/In 2 O 3 and Au/ZrO 2 counterparts. This phenomenon was attributed to a reduced activation energy, a stabilization of indium oxide, a higher amount of oxygen vacancies and a superior CO 2 adsorption.…”

Correlations between the catalyst properties and catalytic activity of Au on ZrO2-CeO2 in the hydrogenation of CO2

“…The ZrO 2 -CeO 2 nanocomposites were synthesized following a precipitation method in a previously published work [27] with slight adjustments. Typically, 4 g of zirconium (IV) oxynitrate (ZrO(NO 3 ) 2 ⋅xH 2 O, Sigma Aldrich) and a predetermined amount of cerium (III) nitrate hexahydrate (Ce(NO 3 ) 3 ⋅6H 2 O, Sigma-Aldrich) was dissolved in 50 mL deionized water resulting in an aqueous solution of 0.1 M Zr 4+ and 0.1x M Ce 3+ , respectively, with x denoted for the Ce to Zr molar ratios (x = n Ce /n Zr ).…”

“…Au-based catalyst is another classic example of the strong dependence between Au particle size and the corresponding catalytic activity [24][25][26]. The highly dispersed Au nanoparticles (≈1 nm) supported on amorphous ZrO 2 via deposition precipitation method provided a much higher methanol formation rate than that of Au/ZrO 2 (d Au ≈50 nm) synthesized by impregnation, i.e., 2.1 > 0.4 g CH3OH • ( g cat • h ) − 1 in the methanol synthesis from CO 2 (240 • C, 40 bar) [27]. It is suggested that the particle size of active metal is strongly associated to the number of interfacial surface area, at which the methanol synthesis has been repeatedly reported to take place [28,29].…”

“…Owing to the great number of uniform acidic sites mainly contributed by Lewis acid sites and a fraction of surface hydroxyl groups as reported in [49], a-ZrO 2 was chosen over monoclinic (m-) and tetragonal (t-) ZrO 2 , two commonly found phases of ZrO 2 . Furthermore, CeO 2 -ZrO 2 mixed oxides were obtained by a simple and low-energy cost coprecipitation method, which is highly desired amid the current energy crisis [27]. Accordingly, a series of Au catalysts supported on CeO 2 -ZrO 2 mixed oxides with a gradually increased molar ratio of Ce to Zr (from 0 to 0.1, with a step of 0.025) was prepared.…”

Accelerated H2 activation over Pt/M-ZrO2 for the reductive amination of levulinic acid esters under benign conditions

“…In continuation of the above studies, altering the physicochemical properties of metal oxides (acidity, basicity, oxygen vacancies, and Lewis acid-base pair) has been investigated and found to strongly influence product distribution. [23][24][25][26][27][28][29][30][31][32][33][34] In line with this, Touchy et al 35 developed Mo-promoted Pt-MoO X /TiO 2 for the reductive amination of LA to OMP at 100 °C, 3 bar H 2 , obtaining a near quantitative yield (99%). Vidal et al 36 prepared Pt/TiO 2 via the deposition-precipitation method for the reductive amination of ethyl levulinate, affording a high selectivity towards the target product at 120 °C under solvent-free conditions.…”