Oxidation of Benzyl Alcohol by using Gold Nanoparticles Supported on Ceria Foam

Abstract

The efficacy of using cerium oxide foams as a support for Au nanoparticles and subsequent use as oxidation catalysts have been investigated. These were synthesized using L-asparagine to produce a cerium coordination polymer foam, which was calcined to give the oxide foam. Au nanoparticles were supported on the CeO(2) foams using a sol-immobilization method. The activity of the Au/foamCeO(2) for solvent-free benzyl alcohol oxidation was superior to standard Au/CeO(2) catalysts, and the activity was found to be dependent on the crystallization time of the precursor foam. A crystallization time of 4 h was found to produce the most active catalyst, which retained activity and a high selectivity to benzaldehyde (ca. 96 %) when re-used and this is related to the structure of the material. The high activity is attributed to the greater lability of surface oxygen in the support compared with commercial CeO(2) materials.

Inhibition of a Gold-Based Catalyst in Benzyl Alcohol Oxidation: Understanding and Remediation

“…It should be noted that for all experimental data points, the mass balance of the 4 main components (BnOH, BnO, BnOOH and BnOOBn) closes to 100% within measurement errors, with rare exceptions where discrepancies up to 4% are present. Therefore, disproportionation and dehydration reactions, as reported by Alhumaimess et al [5], can be neglected. In the first experiment, the initial TOF is 0.7 s −1 and conversion levels off at around 55-60% after about 120 min.…”

“…This exceptionally low process temperature allows for a much better control over the selectivity, in particular in selective oxidations. These reactions play an important role in organic synthesis [1,[5][6][7][8][9][10][11] and, as a consequence, much effort was put into studying and benchmarking gold-based catalysts for selective oxidation of alcohols, ketones, and carboxylic acids.…”

“…Benzyl alcohol (BnOH) selective oxidation to benzaldehyde (BnO) is one of these benchmark reactions used extensively to assess the catalytic activity of gold catalysts [1,[5][6][7][8][9][11][12][13]. Alcohol selective oxidation is often carried out in the presence of a base as "promoter" or "co-catalyst" [1][2][3]7,8,11,12,14,15].…”

“…Furthermore, alkaline conditions have also been reported to enhance the selectivity towards benzoic acid (BnOOH) [1,15]. However, the focus is usually on the initial turnover frequency (TOF) [5,7,12], whereas only a few reports mention issues of deactivation and re-usability [1,6,9,11,14].…”

Gold nanoparticles supported on magnesium oxide as catalysts for the aerobic oxidation of alcohols under alkali-free conditions

“…For these reasons, metal catalyzed oxidations of alcohols, especially those that involve molecular oxygen as a final oxidant, currently attract much attention. Various homogeneous [2,3] and heterogeneous [4][5][6][7][8][9] transition metal catalysts have been reported for the aerobic oxidation of alcohols, with gold nanoparticles (NPs) being among the most promising ones [10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”