Robert Dagle - Academia.edu (original) (raw)

Papers by Robert Dagle

Fuel Cells: Technologies for Fuel Processing, 2011

Description/Abstract A brief review of water gas shift (WGS) catalysis is provided. An overview o... more Description/Abstract A brief review of water gas shift (WGS) catalysis is provided. An overview of the four general classes of WGS catalysts is presented, which include: 1) high temperature shift (HTS), 2) low temperature shift (LTS), 3) sulfur-tolerant shift catalysts, ...

ACS Catalysis, 2013

ABSTRACT In a combined experimental and first-principles density functional theory (DFT) study, b... more ABSTRACT In a combined experimental and first-principles density functional theory (DFT) study, benzene steam reforming (BSR) over MgAl2O4-supported Rh and Ir catalysts was investigated. Experimentally, it has been found that both highly dispersed Rh and Ir clusters (1–2 nm) on the spinel (e.g., MgAl2O4) support are stable during the BSR in the temperature range of 700–850 °C. Compared to the Ir/MgAl2O4 catalyst, the Rh/MgAl2O4 catalyst is more active with higher benzene turnover frequency and conversion. At steam conditions with the molar steam-to-carbon ratio >12, the benzene conversion is only a weak function of the H2O concentration in the feed. This suggests that the initial benzene decomposition step, rather than the benzene adsorption, is most likely the rate-determining step in BSR over supported Rh and Ir catalysts. To understand the differences between the two catalysts, we followed with a comparative DFT study of initial benzene decomposition pathways over two representative model systems for each supported metal (Rh and Ir) catalysts. A periodic terrace (111) surface and an amorphous 50-atom metal cluster with a diameter of 1.0 nm were used to represent the two supported model catalysts under low and high dispersion conditions. Our DFT results show that the decreasing catalyst particle size enhances the benzene decomposition on supported Rh catalysts by lowering both C–C and C–H bond scission. The activation barriers of the C–C and the C–H bond scission decrease from 1.60 and 1.61 eV on the Rh(111) surface to 1.34 and 1.26 eV on the Rh50 cluster. For supported Ir catalysts, the decreasing particle size only affects the C–C scission. The activation barrier of the C–C scission of benzene decreases from 1.60 eV on the Ir(111) surface to 1.35 eV on the Ir50 cluster while the barriers of the C–H scission are practically the same. The experimentally measured higher BSR activity on the supported highly dispersed Rh catalyst can be rationalized by the thermodynamic limitation for the very first C–C bond scission of benzene on the small Ir50 catalyst. The C–C bond scission of benzene on the small Ir50 catalyst is highly endothermic although the barrier is competitive with those of both the C–C and the C–H bond-breaking on the small Rh50 catalyst. The calculations also imply that, for the supported Rh catalysts, the C–C and C–H bond scissions are competitive, independent of the Rh cluster sizes. After the initial dissociation step via either the C–C or the C–H bond scission, the C–H bond breaking seems to be more favorable rather than the C–C bond breaking on the larger Rh terrace surface.

ABSTRACT Methods for producing alcohols from CO or CO.sub.2 and H.sub.2 utilizing a palladium-zin... more ABSTRACT Methods for producing alcohols from CO or CO.sub.2 and H.sub.2 utilizing a palladium-zinc on alumina catalyst are described. Methods of synthesizing alcohols over various catalysts in microchannels are also described. Ethanol, higher alcohols, and other C.sub.2+ oxygenates can produced utilizing Rh--Mn or a Fisher-Tropsch catalyst.

The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.

Applied Catalysis a General, Jul 1, 2007

Selective CO methanation as a strategy for CO removal in fuel processing applications was investi... more Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst activity and selectivity. Even operating at a gas-hourly-space-velocity as high as 13,500 h À1 , a 3% Ru/Al 2 O 3 catalyst with a 34.2 nm crystallite was shown to be capable of reducing CO in a reformate to less than 100 ppm over a wide temperature range from 240 to 280 8C, while keeping hydrogen consumption below 10%. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H 2 and CO 2 .

Catalysis Today, Dec 1, 2002

Pd/ZnO catalysts were investigated for steam reforming of methanol. Unlike precious metal-based c... more Pd/ZnO catalysts were investigated for steam reforming of methanol. Unlike precious metal-based catalysts, Pd/ZnO catalysts not only exhibited high activity, but more importantly very low selectivity to CO for methanol steam reforming. Under the conditions examined, the decomposition activity is minimal. The novel function is attributed to the formation of highly structured Pd-Zn alloy at moderate temperatures under mild reducing environments. The current catalytic system was characterized by TPR, transmission electron microscopy (TEM), H 2 chemisorption, and X-ray diffraction (XRD).

Acs Symposium Series, 2005

The development of a miniaturized hydrogen plant is discussed. The micro-scale system is capable ... more The development of a miniaturized hydrogen plant is discussed. The micro-scale system is capable of producing 1-5 sccm hydrogen that could be used as a fuel supply in a small fuel cell to produce <1 W power. The paper describes the developmental approach, significant unit operations, material selection, and reactor design. The final microscale fuel processing system is composed of

Applied Catalysis B: Environmental, 2016

Fuel Cells: Technologies for Fuel Processing, 2011

Description/Abstract A brief review of water gas shift (WGS) catalysis is provided. An overview o... more Description/Abstract A brief review of water gas shift (WGS) catalysis is provided. An overview of the four general classes of WGS catalysts is presented, which include: 1) high temperature shift (HTS), 2) low temperature shift (LTS), 3) sulfur-tolerant shift catalysts, ...

ACS Catalysis, 2013

ABSTRACT In a combined experimental and first-principles density functional theory (DFT) study, b... more ABSTRACT In a combined experimental and first-principles density functional theory (DFT) study, benzene steam reforming (BSR) over MgAl2O4-supported Rh and Ir catalysts was investigated. Experimentally, it has been found that both highly dispersed Rh and Ir clusters (1–2 nm) on the spinel (e.g., MgAl2O4) support are stable during the BSR in the temperature range of 700–850 °C. Compared to the Ir/MgAl2O4 catalyst, the Rh/MgAl2O4 catalyst is more active with higher benzene turnover frequency and conversion. At steam conditions with the molar steam-to-carbon ratio >12, the benzene conversion is only a weak function of the H2O concentration in the feed. This suggests that the initial benzene decomposition step, rather than the benzene adsorption, is most likely the rate-determining step in BSR over supported Rh and Ir catalysts. To understand the differences between the two catalysts, we followed with a comparative DFT study of initial benzene decomposition pathways over two representative model systems for each supported metal (Rh and Ir) catalysts. A periodic terrace (111) surface and an amorphous 50-atom metal cluster with a diameter of 1.0 nm were used to represent the two supported model catalysts under low and high dispersion conditions. Our DFT results show that the decreasing catalyst particle size enhances the benzene decomposition on supported Rh catalysts by lowering both C–C and C–H bond scission. The activation barriers of the C–C and the C–H bond scission decrease from 1.60 and 1.61 eV on the Rh(111) surface to 1.34 and 1.26 eV on the Rh50 cluster. For supported Ir catalysts, the decreasing particle size only affects the C–C scission. The activation barrier of the C–C scission of benzene decreases from 1.60 eV on the Ir(111) surface to 1.35 eV on the Ir50 cluster while the barriers of the C–H scission are practically the same. The experimentally measured higher BSR activity on the supported highly dispersed Rh catalyst can be rationalized by the thermodynamic limitation for the very first C–C bond scission of benzene on the small Ir50 catalyst. The C–C bond scission of benzene on the small Ir50 catalyst is highly endothermic although the barrier is competitive with those of both the C–C and the C–H bond-breaking on the small Rh50 catalyst. The calculations also imply that, for the supported Rh catalysts, the C–C and C–H bond scissions are competitive, independent of the Rh cluster sizes. After the initial dissociation step via either the C–C or the C–H bond scission, the C–H bond breaking seems to be more favorable rather than the C–C bond breaking on the larger Rh terrace surface.

ABSTRACT Methods for producing alcohols from CO or CO.sub.2 and H.sub.2 utilizing a palladium-zin... more ABSTRACT Methods for producing alcohols from CO or CO.sub.2 and H.sub.2 utilizing a palladium-zinc on alumina catalyst are described. Methods of synthesizing alcohols over various catalysts in microchannels are also described. Ethanol, higher alcohols, and other C.sub.2+ oxygenates can produced utilizing Rh--Mn or a Fisher-Tropsch catalyst.

The Energy Citations Database (ECD) provides access to historical and current research (1948 to t... more The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.

Applied Catalysis a General, Jul 1, 2007

Selective CO methanation as a strategy for CO removal in fuel processing applications was investi... more Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst activity and selectivity. Even operating at a gas-hourly-space-velocity as high as 13,500 h À1 , a 3% Ru/Al 2 O 3 catalyst with a 34.2 nm crystallite was shown to be capable of reducing CO in a reformate to less than 100 ppm over a wide temperature range from 240 to 280 8C, while keeping hydrogen consumption below 10%. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H 2 and CO 2 .

Catalysis Today, Dec 1, 2002

Pd/ZnO catalysts were investigated for steam reforming of methanol. Unlike precious metal-based c... more Pd/ZnO catalysts were investigated for steam reforming of methanol. Unlike precious metal-based catalysts, Pd/ZnO catalysts not only exhibited high activity, but more importantly very low selectivity to CO for methanol steam reforming. Under the conditions examined, the decomposition activity is minimal. The novel function is attributed to the formation of highly structured Pd-Zn alloy at moderate temperatures under mild reducing environments. The current catalytic system was characterized by TPR, transmission electron microscopy (TEM), H 2 chemisorption, and X-ray diffraction (XRD).

Acs Symposium Series, 2005

The development of a miniaturized hydrogen plant is discussed. The micro-scale system is capable ... more The development of a miniaturized hydrogen plant is discussed. The micro-scale system is capable of producing 1-5 sccm hydrogen that could be used as a fuel supply in a small fuel cell to produce <1 W power. The paper describes the developmental approach, significant unit operations, material selection, and reactor design. The final microscale fuel processing system is composed of

Applied Catalysis B: Environmental, 2016