Acrolein Adsorption on Gold Clusters, A Theoretical Study of Conjugation Effect on C=C and C=O Interaction with Au Clust
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Acrolein Adsorption on Gold Clusters, A Theoretical Study of Conjugation Effect on C=C and C=O Interaction with Au Clusters Guo-Jun Kang • Zhao-Xu Chen • Zhe Li
Received: 6 August 2010 / Accepted: 17 September 2010 / Published online: 9 March 2011 Ó Springer Science+Business Media, LLC 2011
Abstract We studied acrolein (AC) adsorption on gold clusters Aun (n = 1–5) using density functional theory. It is demonstrated that conjugation effect reduces the adsorbate– substrate interaction through p-(C=C), p-(C=O) and di-r-(C=O) modes whereas it facilitates the di-r-(C=C) and the r-O configurations. Analysis reveals that in p-(C=C) and p-(C=O) modes acrolein uses the HOMO-1 orbital to interact with the clusters while in r-O mode the HOMO of AC plays the role. For di-r-(C=C), di-r-(C, O) and di-(C=O), the HOMO orbital of the cluster donates electrons to acrolein. Acrolein adsorption through the C=C bond is more favorable than that via the C=O group, which explains why the yields of C=C hydrogenation is higher than that of C=O reduction. Keywords Acrolein Gold clusters Adsorption Conjugation effect
1 Introduction Allyl alcohols which are valuable intermediates used to synthesize pharmaceuticals and flavoring materials [1, 2]
Electronic supplementary material The online version of this article (doi:10.1007/s10562-011-0569-3) contains supplementary material, which is available to authorized users. G.-J. Kang Z.-X. Chen (&) Z. Li Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China e-mail: [email protected] G.-J. Kang Low Carbon Energy Institute, China University of Mining and Technology, Xuzhou 221008, China
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are usually produced from the selective hydrogenation of a, b-unsaturated aldehydes. Normally the C=C bond is more active than the C=O bond both thermodynamically and kinetically [3]. Recently Claus et al. [4, 5] found that the conventionally catalytically inert gold exhibits unexpected activity for the selective hydrogenation of a, b-unsaturated aldehydes to allyl alcohols. It is revealed that gold particles play an important role in gold catalysis and much attention has been paid to gold clusters [6–11]. Acrolein (CH2=CH– CH=O, AC) is the smallest a, b-unsaturated aldehyde and its selective hydrogenation to allyl alcohol is most difficult because there are no substitution groups on the carbon atoms of the C=C bond. Thus it is often used as a model system to establish relations between the selectivity and catalyst structure [12–15]. Adsorption mode is a key factor governing the selectivity of the hydrogenation of a, b-unsaturated aldehyde [16–18]. Therefore, adsorption knowledge of AC on gold clusters should shed light on understanding of the catalytic selectivity of gold to the C=C and C=O groups. AC contains two functional groups that are conjugated together: C=C double bond and C=O group, through which the adsorption is realized. The isolated C=C and C=O can be best
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