Modification of Gold Zeolitic Supports for Catalytic Oxidation of Glucose to Gluconic Acid

Abstract

Activity of gold supported catalysts strongly depends on the type and composition of support, which determine the size of Au nanoparticles (Au NPs), gold-support interaction influencing gold properties, interaction with the reactants and, in this way, the reaction pathway. The aim of this study was to use two types of zeolites: the three dimensional HBeta and the layered two-dimensional MCM-36 as supports for gold, and modification of their properties towards the achievement of different properties in oxidation of glucose to gluconic acid with molecular oxygen and hydrogen peroxide. Such an approach allowed establishment of relationships between the activity of gold catalysts and different parameters such as Au NPs size, electronic properties of gold, structure and acidity of the supports. The zeolites were modified with (3-aminopropyl)-trimethoxysilane (APMS), which affected the support features and Au NPs properties. Moreover, the modification of the zeolite lattice with boron was applied to change the strength of the zeolite acidity. All modifications resulted in changes in glucose conversion, while maintaining high selectivity to gluconic acid. The most important findings include the differences in the reaction steps limiting the reaction rate depending on the nature of the oxidant applied (oxygen vs. H2O2), the important role of porosity of the zeolite supports, and accumulation of negative charge on Au NPs in catalytic oxidation of glucose.

Microwave-Assisted Base-Free Oxidation of Glucose with H2O2 on Gold- and Manganese-Containing SBA-15—Insight into Factors Affecting the Reaction Pathway

“…The use of MnSBA-15 molecular sieves as supports for gold assumed the possible interaction of gold and manganese species and in this way modification of gold particle size and electronic properties. Therefore, the results obtained for this system are expected to answer the question about the role of accumulation of negative charge on gold nanoparticles (AuNPs), postulated as one of the important features in chemisorption and transformation of hydrogen peroxide [13] and the catalyst activity. The impact of manganese dopant on the size of Au NPs and the catalyst activity would also be considered.…”

“…This target product and its derivatives are generally used in the food industry as acidity regulators, and as additives in the pharmaceutical, building, and textile industries [4]. Au-based catalysts (e.g., Au/C, Au/Al 2 O 3 , Au/TiO 2 ) [4][5][6][7][8][9][10], Au-zeolites, and Au-mesoporous silicas [4,[11][12][13]) were found to be active and selective for the oxidation of glucose to gluconic acid under basic and base-free conditions. Molecular oxygen has been most often used as an oxidant in this reaction.…”

“…Moreover, the combined use of microwave irradiation and heterogeneous catalysts gives an additional benefit of easy separation of the catalyst and products. It is important to note, that to the best of our knowledge, there are only a few studies dedicated to microwave-assisted glucose oxidation [9,10,13].…”

“…For base-free microwave-assisted glucose oxidation with hydrogen peroxide on Au/Al 2 O 3 , Rautiainen et al [9] have shown a correlation between the rate of oxygen formation and the activity of gold catalysts. Walkowiak et al [13] have suggested that the rate limiting step in microwave-assisted glucose oxidation with H 2 O 2 performed on gold-modified zeolites is chemisorption and decomposition of the oxidant. Moreover, the authors concluded that there is no correlation between BrØnsted acid sites (BASstrength and/or number) of the zeolite support on which glucose can be chemisorbed and the activity in glucose oxidation with H 2 O 2 , in contrast to the oxidation of glucose with molecular oxygen in which the enhancement in glucose conversion was related to some extent to the increase in glucose chemisorption on BrØnsted acid sites (BAS).…”

“…The idea of this study was not only to use the gold support containing LAS without BAS, but also to construct catalysts with different textural parameters (especially different pore sizes) but with the same elemental composition and structure. Recently [13] it has been established that for the same gold particle size the activity of Au/MCM-36 in basefree and microwave-assisted glucose oxidation with hydrogen peroxide was higher than that of Au/HBeta zeolites. This was attributed to the larger pores in the first zeolite.…”