Structure and Stability of AG-IR Bimetallic Catalysts Prepared By Electroless Deposition and Synthesis and Performance of High Selectivity Movnbsbteox Mixed Oxides for Oxidative Dehydrogenation of Ethane
Date of Award
Open Access Dissertation
John R. Regalbuto
John R. Monnier
Improvements in industrial thermal conversions can be realized through comprehensive catalytic studies, where enhanced catalyst stability and activity are desired. Catalyst performance can be greatly affected by structural changes at high temperatures. In the case of supported Ag-Ir particles, the surface free energy (SFE) can determine preferred arrangement of the component metals. The well-established methods of strong electrostatic adsorption (SEA) and electroless deposition (ED) have been used to synthesize highly-dispersed Ag/Ir on different alumina supports (δ,θ-Al2O3 and γ-Al2O3). Surface thermodynamics dictate that the Ir-Ag system should conform to minimize free energy resulting in a low SFE Ag layer localized on the high SFE Ir surface. XRD data and STEM images indicate that both monometallic catalysts sintered, but deposition of a Ag shell by ED prevented the sintering of both Ag and Ir. H2 TPD measurements corroborate the high H2 uptake chemisorption experiments, indicating the additional H2 capacity was due to more weakly-bound H, which computational and XPS results confirm.
In light olefin production from ethane, selective catalytic oxidative dehydrogenation (ODH) represents an alternative to thermal dehydrogenation, where the latter requires temperatures exceeding 1100⁰C. ODH can achieve similar ethylene space-time yields using a catalytic process operating at 300-600 ⁰C. Complex multicomponent oxides have been shown to be effective ODH catalysts, with significant findings suggesting exceptional performance of Te-containing MoVNb mixed oxides. MoVNbTe(Sb)Ox M1-phase catalysts were synthesized using a slurry method in accordance with previous techniques disclosed in patent literature. Different parameters, i.e. compositions and thermal treatments, in synthesis and their effects on catalyst performance were studied. Catalysts were characterized by using XRD, SEM, BET, and XRF. It was determined that Te has a structural effect during synthesis and lack thereof results in no catalyst activity. A complete kinetic study for the same M1-phase catalyst was done including reactant (C2H6, O2) and product (C2H4, CO2, and H2O) reaction orders. Three pressures of 0, 60, and 120psig and three temperatures of 275, 310, and 350°C were used. The activation energies of ethane consumption and products formation were calculated. Higher reaction orders of ethane for ethylene formation compared to combustion products formation suggest ethane rich feed for optimal reaction condition. Low temperature operation is preferred to avoid non-selective product formation and an oxygen lean environment is suggested to prevent deactivation of the catalyst via partial reduction.
Parizad, M.(2021). Structure and Stability of AG-IR Bimetallic Catalysts Prepared By Electroless Deposition and Synthesis and Performance of High Selectivity Movnbsbteox Mixed Oxides for Oxidative Dehydrogenation of Ethane. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6601
Available for download on Thursday, December 15, 2022