Title

Sustainable Transformation of Biorenewables Mediated by Rationally Designed Nanoparticle Catalysts

Date of Award

6-2018

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dr. Sherine O. Obare

Second Advisor

Dr. Ekkehard Sinn

Third Advisor

Dr. Ramakrishna Guda

Fourth Advisor

Dr. Massood Atashbar

Abstract

In spite of recent discoveries and technological advances that have maintained US crude oil supplies, there remains a need for biorenewables to replace crude oil as the primary feedstock for chemicals and fuels. The governing hypothesis is that highly selective catalysts will promote the conversion of biorenewable feedstocks to commodity chemicals under sustainable and ambient conditions, resulting in the overall cost-reduction for their production. To address this hypothesis, novel catalysts consisting of metallic and bimetallic nanoparticles with controlled size have been designed through novel facile procedures. Platinum group metals are well recognized as high performance catalysts. Changing the metal size to the nanoscale enhances the catalytic efficiency, due to the high surface area to volume ratio of the nanoparticles. Metallic nanoparticles dimensions have great influence on the catalytic efficiency and selectivity. This dissertation work focuses on designing palladium and ruthenium monometallic nanoparticles due to their selectivity for the hydrogenation of unsaturated bonds. Furthermore, we developed a new method for the synthesis of palladium-ruthenium bimetallic nanoparticles in a mixed alloy structure. Various synthetic parameters were optimized to obtain monodisperse bimetallic nanoparticles. Both monometallic and bimetallic nanoparticles were synthesized as colloidal solutions. Due to the catalysts and the reactions being in the same phase, heterogenous catalyst is necessary. Therefore, mesoporous silica was used to support the nanoparticles to make it heterogeneous catalyst. The catalytic efficiency and selectivity for the catalysts were investigated toward the hydrogenation and semihydrogenation of C=C bond in model organic compounds. Palladium and ruthenium monometallic nanoparticles showed high selective hydrogenation for unsaturated C=C bond and C=O bond, respectively. Bimetallic palladium-ruthenium nanoparticles catalysts showed excellent efficiency for the hydrogenation of all model organic compounds and semi-hydrogenation of compounds containing other unsaturated bonds. Moreover, an organic compound containing conjugated C=C bond with imine group via Schiff base method. The bimetallic catalyst showed selective hydrogenation for C=C bond rather than C=N group. Low hydrogenation selectivity was obtained for C=C bond in trans-cinnamaldehyde, due to the presence of palladium and ruthenium in one catalyst as an alloy, where both unsaturated group hydrogenated (C=C bond and carbonyl group). The protection of carbonyl group via acetalization with alcohol was used to overcome this issue. We modified the catalyst by removing the stabilizing ligands (n-dodecyl sulfide) by calcination, which activated the catalyst surface. Modified catalysts showed high to excellent conversion and selectivity for the acetalization of different aliphatic and aromatic aldehydes. The modified catalyst showed the acetalization of trans-cinnamaldehyde with methanol. The bimetallic catalyst remained active in further hydrogenation reaction. Therefore, we investigated their ability to mediate tandem acetalization and hydrogenation reactions. The results showed conversion for both reactions for 96% within 4-6 hours using Pd-Ru bimetallic catalyst. The reactions described in this thesis are of great importance for different industrial applications, for instance, biomass conversion into commodity chemicals. In addition, all reactions were performed at room temperature and ambient hydrogen pressure.

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Dissertation-Abstract Only

Restricted to Campus until

6-2028

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