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Flaherty, David W. Flaherty, David W. Seebauer, Edmund Yang, Hong Rodríguez-López, Joaquín Chang, SiWei 2018-03-13T15:45:14Z 2018-03-13T15:45:14Z 2017-11-16 2017-12 Transition metal phosphide (TMP) catalysts are selective and active towards C-O bond rupture during hydrodeoxygenation (HDO) of oxygenates, making them potential candidates for bio-oil upgrading. However, the mechanism by which the C-X (X = O, C, H) bond ruptures and the corresponding intrinsic barriers (i.e., for C-H, C-C, and C-O bond rupture) between transition metals and TMP catalysts are not well understood. Here, we synthesized and characterized a phosphorus (P) modified Ru(0001) surface by annealing Ru(0001) in the presence of PH3 gas under ultra-high vacuum conditions to produce Px-Ru(0001) (x is the ratio of P atoms to Ru atoms). The P0.43-Ru(0001) surface has a √7 x √7 low energy electron diffraction pattern, which is structurally similar to the (111) facet of well-characterized bulk Ru2P. Temperature programmed desorption measurements of CO and NH3 showed that the addition of P atoms decrease the binding energy of CO by up to 30 kJ mol-1 and NH3 by 14 kJ mol-1 as compared to pristine Ru(0001). This suggests that P atoms decrease the extent of electron exchange between Ru surfaces and adsorbates. We examined the decomposition of C1-C4 carboxylic acid (e.g., formic acid (FA), acetic acid (AA), propionic acid (PA), and butyric acid (BA)) on pristine Ru(0001) and P0.4-Ru(0001) surfaces. Temperature programmed reaction (TPR) and reactive molecular beam scattering (RMBS) experiments were used to determine bond rupture barriers and selectivity of C-O bond rupture compared to C-H/C-C bond rupture. The TPR results showed that longer alkyl carbon chains can promote self-stabilizing lateral interactions between carboxylates via dispersive (van der Waals) interactions, which is evidenced by increases in intrinsic activation energy (Ea) (1-5 kJ mol-1) for R-COOH bond rupture. RMBS of FA demonstrated that apparent activation energies (Eapp) of dehydration and dehydrogenation are greater on P0.43-Ru(0001) by 27 kJ mol-1 and 33 kJ mol-1, respectively, compared to Ru at temperatures greater than 500 K. Additionally, FA decomposition over P0.43-Ru(0001) is more selective toward C-O bond rupture than C-H bond rupture. Moreover, the addition of P atoms to Ru(0001) increases Ea values for all bonds (i.e., C-O, C-H and C-C bonds) by 5-50 kJ mol-1, which suggests that P-atoms decrease Ru surface electron back donation toward all adsorbates and changes the product selectivity by increasing energy barriers for C-O bond rupture more than C-H/C-C bond rupture. Collectively, these data and interpretations led to a proposed a set of elementary steps for carboxylic acid decomposition over Px-Ru(0001) and Ru(0001) surfaces. The results may provide guidance for the design of more selective P-modified transition metal catalysts to surgically cleave C-O bonds and convert biomass derived intermediates into platform chemicals and fuels. TMP catalysts are also active for alkane dehydrogenation, which is especially useful given the recent discovery of large shale-gas reserves. Here, we studied the effect of P atom on light alkane dehydrogenation and coke formation (i.e., a problem common to dehydrogenation catalysts) using Ru(0001). Cyclohexene was used as a probe molecule, and the RMBS of cyclohexene demonstrated that the addition of P atoms enhances the selectivity of cyclohexene dehydrogenation relative to cyclohexene decomposition (i.e., coking) by a factor great than 10 when compared to selectivities on Ru(0001). The change in dehydrogenation selectivity is caused by P atoms decreasing the Eapp for benzene formation by 12 kJ mol-1 while increasing Eapp for coking by 11 kJ mol-1. Additionally, TPR experiments showed that the addition of P atoms to Ru(0001) minimized cyclohexene coking when compared to Ru(0001). Thus, this work shows that TMP catalysts possess enormous potential for use as selective dehydrogenation catalysts. Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2018-03-13 without embargo terms The student, SiWei Chang, accepted the attached license on 2017-11-12 at 09:28. The student, SiWei Chang, submitted this Dissertation for approval on 2017-11-12 at 09:34. This Dissertation was approved for publication on 2017-11-16 at 17:07. DSpace SAF Submission Ingestion Package generated from Vireo submission #11733 on 2018-03-13 at 10:08:32 Made available in DSpace on 2018-03-13T15:45:14Z (GMT). No. of bitstreams: 3 CHANG-DISSERTATION-2017.pdf: 2759264 bytes, checksum: 2923e714a1dbefc3965f8bef170d9a5b (MD5) LICENSE.txt: 4208 bytes, checksum: 95c87616667f9eed06473a7de1c42a63 (MD5) PROQUEST_LICENSE.txt: 4554 bytes, checksum: c04f258577c711f19f9723108b0375d9 (MD5) Previous issue date: 2017-11-16 application/pdf http://hdl.handle.net/2142/99325 en Copyright 2017 SiWei Chang Heterogeneous catalyst Transition metal phosphide Surface science Bio-oil hydrodeoxygenation Light alkane dehydrogenation Carboxylic acid Cyclohexene Effects of phosphorus on bond rupture during hydrodeoxygenation and dehydrogenation reactions on ruthenium text text Chemical & Biomolecular Engr Chemical Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.