A Study of Catalytic Oxidation of a Library of C2 to C4 Alcohols in the Presence of Nanogold

Abstract

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO2, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H2O2 as a clean oxidant. We tested different levels of Au loading (0.1–1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au–Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation—the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO2 at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO2 might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Desenvolvimento de um catalisador de ouro e paládio e o impacto da calcinação na oxidação seletiva do álcool benzílico

“…Todo o posterior desenvolvimento dos catalisadores de ouro veio da mão do estudo pioneiro feito por Haruta et al (1987) [37], no qual descobriram a peculiaridade dos catalisadores de ouro na oxidação de CO. Este estudo levou os catalisadores de ouro a alcançar um lugar especial no campo da catálise. Mais tarde diferentes descobertas revelaram que a capacidade catalítica do ouro está relacionada com a dimensão das suas partículas, isto é, as partículas de menor tamanho possuem maior capacidade de absorção dos substratos e com isso uma maior possibilidade de efetuar o processo catalítico [38]. Por exemplo, Mavrikakis et al (2000) [39], demonstraram que um dos parâmetros mais importantes que determina a reatividade das nanopartículas de Au é a densidade de camada.…”