The effects of alkali promoters on the dynamics of hydrogen chemisorption and syngas reaction kinetics on Ru/SiO2 surfaces

Üner, Deniz
Pruski, M
King, TS
The dynamics of chemisorbed hydrogen on unpromoted and promoted Ru/SiO2 catalysts was studied by means of single pulse and selective excitation H-1 NMR spectroscopy. Dynamic NMR studies indicated a reduced mobility of hydrogen in the presence of alkali promoters (Na and K) at high loadings (65 atomic %). On unpromoted Ru/SiO2 catalysts, the line due to hydrogen-on-metal was homogeneously broadened at pressures above 0.5 Torr H-2. Similar behavior was observed on promoted Ru/SiO2 catalyst with 66 atomic % K. The line due to hydrogen-on-metal was inhomogeneously broadened at least up to 200 Torr H-2 on promoted Ru catalyst with 66 atomic % K. A similar behavior was observed on a 65 atomic % Na promoted catalyst up to pressures of 735 torr and temperatures up to 630 K. A homogeneous lineshape indicates that there is fast exchange of hydrogen among different Ru particles whereas an inhomogeneous line indicates that such an inter-particle motion is restricted. The exchange parameter of hydrogen motion was determined from a multisite exchange model. It was determined that this exchange parameter on unpromoted Ru catalysts was 20 fold higher than that on a K/Ru catalyst with 66% K at a given hydrogen pressure. The mechanism for this inhibited mobility was postulated as follows: Alkali blocked the low coordination sites needed for dissociative chemisorption of hydrogen and the kinetics of adsorption-desorption was thereby slowed down significantly. Good quantitative agreement was obtained when the exchange parameters are used to determine the effects of alkali promoters on olefin selectivities in Fischer Tropsch synthesis reaction.


The effect of lime addition on the combustion properties and sulfur contents of three different coals
Ozbas, Kazim Esber; Hiçyilmaz, Cahit; Kök, Mustafa Verşan (2002-01-01)
In this research, combustion characterization of 3 different coals of Turkey, from the Soma, Tuncbilek, and Afsin Elbistan regions, were investigated with thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). Lime was added to these coals in concentrations of 3, 7, and 10% by weight to investigate the change in combustible sulfur content and sulfur in ash. It was observed that lime has a positive effect on sulfur emission. Kinetic analysis was also perfor...
A Density Functional Theory Study of NO Reduction by C3H8 Aided Selective Catalytic Reduction Method
Tezsevin, Ilker; Onay, Deniz; FELLAH, MEHMET FERDİ; Önal, Işık (2015-03-01)
In this theoretical work sequential adsorption of H-2 and O-2 on a Ag (7) (+) cluster surface is first studied and Ag (7) (+) H2O2 cluster co-complex thereby obtained is used for the NO reduction process. This cationic charged silver nano cluster simulates small Ag crystals experimentally detected on gamma-Al2O3 support. For NO reduction, three different mechanisms and intermediate steps of these mechanisms reported in experimental literature are examined. Energy profiles, activation barriers and transition...
The role of alkali-metal promotion on CO oxidation over PdO/SnO2 catalysts
MİRKELAMOĞLU, BURCU; Karakaş, Gürkan (Elsevier BV, 2006-01-17)
Sol-gel prepared PdO/SnO2 and Na-PdO/SnO2 catalysts were investigated by X-ray photoelectron spectroscopy (XPS), diffuse reflectance IR (DRIFTS), temperature-programmed reaction spectroscopy (TPRS) and impulse techniques. Alkali-metal promotion was observed to enhance CO oxidation rate and decreases light-off temperatures of PdO/SnO, XPS analysis revealed that alkali-metal promotion resulted in the segregation of Pd atoms and promoted the oxygen storage capacity of the catalysts. The presence of super-oxide...
Kinetics of hydrogen adsorption and Desorption on silica-supported Pt, Rh, and Ru catalysts studied by solid state H-1 NMR
Savargaonkar, N; Üner, Deniz; Pruski, M; King, TS (2002-05-14)
The kinetics of adsorption and desorption of hydrogen on the multifaceted surfaces of silica-supported Pt, Rh, and Ru catalysts were studied by means of solid state H-1 NMR. Experiments with selective inversion of 1H magnetization and the formalism developed by Engelke et al. [J. Chem. Phys. 1994, 101 (9), 7262] were used to extract the adsorption and desorption rate constants and the apparent sticking coefficient. The sticking coefficients of hydrogen measured at 333 K at a surface coverage of 0.4 over 5% ...
A quantum chemical study of nitric oxide reduction by ammonia (SCR reaction) on V2O5 catalyst surface
Soyer, Sezen; Uzun, Alper; Senkan, Selim; Önal, Işık (2006-12-15)
The reaction mechanism for the selective catalytic reduction (SCR) of nitric oxide by ammonia on (010) V2O5 surface represented by a V2O9H8 cluster was simulated by means of density functional theory (DFT) calculations performed at B3LYP/6-31G** level. The computations indicated that SCR reaction consisted of three main parts. For the first part, ammonia activation on V2O5 was investigated. Ammonia was adsorbed on Bronsted acidic V-OH site as NH4+ species by a non-activated process with an exothermic relati...
Citation Formats
D. Üner, M. Pruski, and T. King, “The effects of alkali promoters on the dynamics of hydrogen chemisorption and syngas reaction kinetics on Ru/SiO2 surfaces,” DYNAMICS OF SURFACES AND REACTION KINETICS IN HETEROGENEOUS CATALYSIS, pp. 315–324, 1997, Accessed: 00, 2020. [Online]. Available: