Influence of Co-Precipitation Agent on the Structure, Texture and Catalytic Activity of Au-CeO2 Catalysts in Low-Temperature Oxidation of Benzyl Alcohol

Abstract

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation; hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

Synthesis of active, robust and cationic Au25 cluster catalysts on double metal hydroxide by long-term oxidative aging of Au25(SR)18

“…To the best of our knowledge, this TOF value is among the highest reported for Au catalysts under similar conditions (Table S4†). 27,29,31,51–58 The catalytic conversion was completely stopped upon removing the catalyst by filtration (Fig. 4A), indicating that Au 25 /Co 3 Ce acted as a truly heterogeneous catalyst.…”

Insight into the Role of the Amino‐Organosilane Modifier in Improving the Catalytic Activity of ZnO‐Supported Gold Species in Base‐Free Oxidation of Benzyl Alcohol

“…According to the previous studies, size of Au NPs is one of the factors affecting the selectivity in benzyl alcohol oxidation. [32] In general, smaller Au NPs are more effective in oxidation of BnOH to benzaldehyde and its further oxidation to benzoic acid than the larger ones. Thus, higher selectivity to benzaldehyde observed for the reused catalyst is in line with TEM observations showing slight agglomeration of Au NPs in AuÀ NH 2 À ZnO catalyst during BnOH oxidation.…”

Au/CeO2 Photocatalyst for the Selective Oxidation of Aromatic Alcohols in Water under UV, Visible and Solar Irradiation

“…Wolski et al prepared three CeO 2 samples using different co-precipitation agents (urea, hexamethylenetetramine or NaOH) and Au-loaded photocatalysts. The catalytic study was carried out in dark condition at 40 • C (thermal catalysis) and evidenced that the most active catalysts (highest conversion of benzyl alcohol) were those containing gold and in particular the one prepared by using NaOH as co-precipitation agent [19]. The results obtained by Wolski et al are not comparable with those reported in this work but indicate that, in order to avoid the over oxidation of benzyl alcohol to benzoic acid, it is better to carry out the experiments at room temperature, as in our case.…”

“…According to the literature, the most important factors influencing the activity and selectivity of Au/CeO 2 as thermal catalysts for the partial oxidation of benzyl alcohols are the size of the supported gold nanoparticles [17] and the concentration of lattice defects in the ceria support [18]. Wolsky et al report that the use of NaOH as precipitation (or coprecipitation) agent instead of urea or hexamethylenetetramine in the CeO 2 preparation has a significant impact on the structure, texture and catalytic properties of Au/CeO 2 catalysts resulting beneficial in the formation of small and uniform gold nanoparticles possessing enhanced catalytic activity s in low-temperature oxidation of benzyl alcohol [19].…”