Dependence of Gas-Phase Crotonaldehyde Hydrogenation Selectivity and Activity on the Size of Pt Nanoparticles (1.7–7.1 nm) Supported on SBA-15

Abstract

Running title: Influence of particle size on selectivity during crotonaldehyde hydrogenation 2 AbstractThe selectivity and activity for the hydrogenation of crotonaldehyde to crotyl alcohol and butyraldehyde was studied over a series of Pt nanoparticles (diameter of 1.7, 2.9, 3.6, and 7.1 nm). The nanoparticles were synthesized by the reduction of chloroplatinic acid by alcohol in the presence of poly(vinylpyrrolidone) (PVP), followed by encapsulation into mesoporous SBA-15 silica. The rate of crotonaldehyde hydrogenation and selectivity towards crotyl alcohol both increase with increasing particle size. , The selectivity towards crotyl alcohol increased from 13.7 % to 33.9 % (8 Torr crotonaldehyde, 160 Torr H 2 and 353 K), while the turnover frequency increases from 2.1 × 10 -2 s -1 to 4.8 × 10 -2 s -1 with an increase in the particle size from 1.7 nm to 7.1 nm. The decarbonylation pathway to form propene and CO is enhanced over the higher proportion of coordinatively unsaturated sites on the smaller nanoparticles. The apparent activation energy remains constant (~ 16 kcal mol -1 for the formation of butyraldehyde and ~ 8 kcal mol -1 for the formation of crotyl alcohol) as a function of particle size. In the presence of 130 -260 mTorr CO, the reaction rate decreases for all products with a CO reaction order of -0.9 for crotyl alcohol and butyraldehyde over 7.1 nm Pt particles; over 1.7 nm Pt particles, the order in CO is -1.4 and -0.9, respectively. Hydrogen reduction at 673 K after calcination in oxygen results in increased activity and selectivity relative to reduction at either higher or lower temperature; this is discussed with regards to the incomplete removal and/or change in morphology of the polymeric surface stabilizing agent, poly(vinylpyrrolidone) used for the synthesis of the Pt nanoparticles..3

Nanocatalysis I: Synthesis of Metal and Bimetallic Nanoparticles and Porous Oxides and Their Catalytic Reaction Studies

“…The size of nanoparticles influences not only the reaction rate but also the product selectivity. Many hydrogenation reactions of small molecules including pyrrole [53], furan [54], crotonaldehyde [55], butadiene [56], furfural [57], methylcyclopentane [58], cyclohexene [59], and nhexane [60] have been proven to change their selectivity by Pt nanoparticle size or shape. For example, in 1,3-butadiene hydrogenation, 0.9 and 1.8 nm Pt nanoparticles increased the production of n-butane by full hydrogenation, whereas 4.6 and 6.7 nm Pt catalysts favored 1-butene by partial hydrogenation [56].…”

Monitoring in situ the colloidal synthesis of AuRh/TiO2 selective-hydrogenation nanocatalysts

“…The selective hydrogenation of cinnamaldehyde (CALD) [14][15][16] to hydrocinnamaldehyde (HCALD) is of interest for avor and fragrance industries. 17 Moreover, the reaction is structure-sensitive, as its performance depends on the type of exposed crystallographic planes, 18-21 the nature and size of the metallic NPs, 17,19,[22][23][24][25][26] and the nature of the support. 22,23 Some studies have shown the interest of using TiO 2 as a support for modifying the activity and the selectivity of Au NPs.…”

Catalytic hydrogenation of benzaldehydes over platinum nanoparticles immobilized on magnesium aluminate spinel under mild conditions

“…Generally, supported catalysts are simply prepared by the impregnation of supports in aqueous solutions of metal salts, where morphologies of the supported metals are difficult to control. The effect of the shape and size of supported nanoparticles on catalytic activity has been reported, and both the selectivity and activity of these catalysts are influenced by these factors [12][13][14][15]. Methods have been developed to obtain monodispersed nanoparticles with controllable compositions, structures, sizes, and shapes.…”