Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons

Abstract

The size of the active phase is one of the most important factors in determining the catalytic behaviour of a heterogeneous catalyst. This Feature Article focuses on the size effects in two types of reactions, i.e., the metal nanoparticle-catalysed dehydrogenation of alcohols and the metal oxide nanocluster-catalysed selective oxidation of hydrocarbons (including the selective oxidation of methane and ethane and the epoxidation of propylene). For Pd or Au nanoparticle-catalysed oxidative or non-oxidative dehydrogenation of alcohols, the size of metal nanoparticles mainly controls the catalytic activity by affecting the activation of reactants (either alcohol or O(2)). The size of oxidic molybdenum species loaded on SBA-15 determines not only the activity but also the selectivity of oxygenates in the selective oxidation of ethane; highly dispersed molybdenum species are suitable for acetaldehyde formation, while molybdenum oxide nanoparticles exhibit higher formaldehyde selectivity. Cu(II) and Fe(III) isolated on mesoporous silica are highly efficient for the selective oxidation of methane to formaldehyde, while the corresponding oxide clusters mainly catalyse the complete oxidation of methane. The lattice oxygen in iron or copper oxide clusters is responsible for the complete oxidation, while the isolated Cu(I) or Fe(II) generated during the reaction can activate molecular oxygen forming active oxygen species for the selective oxidation of methane. Highly dispersed Cu(I) and Fe(II) species also function for the epoxidation of propylene by O(2) and N(2)O, respectively. Alkali metal ions work as promoters for the epoxidation of propylene by enhancing the dispersion of copper or iron species and weakening the acidity.

Matching the organic and inorganic counterparts during nucleation and growth of copper-based nanoparticles – in situ spectroscopic studies

“…It is the product of the oxidation of benzyl alcohol according to the reaction shown in Scheme 1. 54 The amounts of dibenzyl ether and benzyl benzoate detected by GC-MS are obviously below the detection limit of FTIR. Now we discuss the quantities of the two compounds benzyl acetate and benzaldehyde we measured in comparison to what would be expected from the proposed chemical reactions.…”

“…[54][55][56][57] Scheme 3 Oxidation of benzyl alcohol to benzaldehyde and reduction of Cu 2+ to Cu + (a) and Cu + to Cu 0 (b).…”

Factors influencing the catalytic oxidation of benzyl alcohol using supported phosphine-capped gold nanoparticles

“…that a gold-based catalyst could be used in the hydrochlorination of acetylene. 2 These discoveries triggered a revolution in gold-based catalysis, with numerous follow-up papers demonstrating the superiority of gold-based catalysts over the more expensive platinum group metals in various catalytic 30 processes, with improvements in activity, selectivity and stability against deactivation paving a pathway to numerous commercially-oriented patents. 3,4 The number of studies on nanoparticulate gold-based catalysts for a broad range of bulk and fine chemical synthesis processes has grown exponentially.…”

Controllable Catalysis with Nanoparticles: Bimetallic Alloy Systems and Surface Adsorbates

“…[17][18][19][20][21] Small particle size is often a prerequisite of their high catalytic competency; however, the optimal size cannot be predicted a priori. 7,[22][23][24][25][26] NP catalysts are extremely useful, yet in many cases they remain Dinge an sich. Strategies for the rational design of NP catalysts and better mechanistic understanding of the underlying reaction mechanisms are highly desirable.…”