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Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnama.pdf (1.57 MB)

Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

preprint
submitted on 16.09.2020 and posted on 17.09.2020 by Surya Kumar Vatti, Kandasamy Konda R Krishnamurthy, Balasubramanian Viswanathan

Uniform-spherical Pd nanoparticles (NPs) supported catalysts were prepared by a mild-temperature chemical reduction method. Pd colloidal suspension was wet-impregnated on various supports, P25-TiO2, SiO2, and γ-Al2O3. In XPS, asymmetric Pd 3d5/2 peak reveals % surface concentration of Pd2+ and Pd0 species. The surface Pd2+/Pd0 ratio on the catalyst surface varied between ~1 to 0.15 depending on strong-metal support interactions (SMSI) inferred from XPS and H2-TPR studies. A linear correlation between Pd2+/Pd0 ratio and turnover frequency (TOF) was observed, with 1% Pd/P25-TiO2 showing the highest TOF/selectivity with Pd2+/Pd0 ratio ~1.0, whereas 1% Pd/γ-Al2O3 showed the lowest TOF/selectivity with lowest Pd2+/Pd0 ratio 0.15. Interestingly, H2-TPR reveals PdH decomposition peaks along with the Ti4+ reduction peak, and XPS Ti 2p of 1% Pd/P25-TiO2 indicates the presence of Ti3+ in TiO2 lattice, which may have generated due to H2-spillover from Pd to P25-TiO2. Hence, we observed excellent COL selectivity (~90%) and 100 % conversion with 1.5% Pd/P25-TiO2 catalyst. Excellent COL selectivity may be ascribed to small Pd NPs (~3 nm) with intrinsic surface electropositive sites (Pd2+) created by partial reduction on the catalyst surface along with SMSI. These electropositive sites (Pd2+) promote preferential C=O adsorption. On the other hand, post-reduced catalyst in H2 @300 °C (1% Pd/P25-TiO2-PRH2) with large Pd NPs (~7 nm) showed significant selectivity loss (>50 %), which confirm significance of small Pd NPs with electropositive sites.

Funding

Department of Science & Technology, Government of India,

History

Email Address of Submitting Author

suryakumarvatti@gmail.com

Institution

National Centre for Catalysis Research, Indian Institute of Technology Madras

Country

India

ORCID For Submitting Author

0000-0002-1439-1845

Declaration of Conflict of Interest

There are no conflicts to declare

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