Johannes Schwank - Academia.edu (original) (raw)

Papers by Johannes Schwank

Journal of Catalysis, 1992

A series of Pt-Sn/A1203 catalysts supported on Degussa nonporous alumina were characterized by in... more A series of Pt-Sn/A1203 catalysts supported on Degussa nonporous alumina were characterized by infrared spectroscopy of adsorbed CO. The nominal platinum loading was kept constant in the catalysts at l wt% and the nominal amount of tin was varied from 0 to 5 wt%. At room temperature it was found that there was a general trend for the linearly adsorbed CO band to shift to lower frequencies with increasing amounts of tin in the catalyst, except for one of the catalysts (1.0 Pt-1.0 Sn/AI203) where a particle size effect seemed to be dominant. The amount of bridge-bonded CO species was very small and became undetectable in the case of large tin loadings (1 and 5 wt% Sn). Thermal desorption infrared spectroscopy was used to determine the vibration frequency of the isolated CO molecule and hence observe if there were any indications of electronic interactions between tin and platinum. For the monometallic 1.0 Pt/A1203 sample the singleton vibration frequency was 2041 cm-t. For all the Pt-Sn bimetallic samples it was found that the singleton vibration frequency lay within the range 2041-+ 6 cm-1. This suggests that the electronic effect of Sn on Pt in our Pt-Sn/A120 3 catalysts is not very large.

Frontiers of Chemical Science and Engineering, 2017

A significant portion of the world’s population does not have access to safe drinking water. This... more A significant portion of the world’s population does not have access to safe drinking water. This problem is most acute in remote, resource-constrained rural settings in developing countries. Water filtration using activated carbon is one of the important steps in treating contaminated water. Lignocellulosic biomass is generally available in abundance in such locations, such as the African rain forests. Our work is focused on developing a simple method to synthesize activated biochar from locally available materials. The preparation of activated biochar with diammonium hydrogenphosphate (DAP) as the activating agent is explored under N2 flow and air. The study, carried out with cellulose as a model biomass, provides some insight into the interaction between DAP and biomass, as well as the char forming mechanism. Various characterization techniques such as N2 physisorption, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy are utilized to compare the properties between biochar formed under nitrogen and partial oxidative conditions. At a temperature of 450 °C, the loading of DAP over cellulose is systematically varied, and its effect on activation is examined. The activated biochar samples are predominantly microporous in the range of concentrations studied. The interaction of DAP with cellulose is investigated and the nature of bonding of the heteroatoms to the carbonaceous matrix is elucidated. The results indicate that the quality of biochar prepared under partial oxidation condition is comparable to that of biochar prepared under nitrogen, leading to the possibility of an activated biochar production scheme on a small scale in resource-constrained settings.

Introduction Fuel cells, which produce electricity directly from hydrogen and oxygen, offer a cle... more Introduction Fuel cells, which produce electricity directly from hydrogen and oxygen, offer a clean and efficient potential alternative to internal combustion engines for generating power for portable and transportation applications. However, there currently is no infrastructure for the wide scale production and distribution of hydrogen to the transportation market. Instead of building new infrastructure, it is possible to produce hydrogen on-demand from common hydrocarbon fuels. [1] Several catalytic processes can be used to produce hydrogen from hydrocarbons. The most common are partial oxidation (POX), steam reforming (SR), and autothermal reforming (ATR), all of which produce primarily hydrogen, carbon monoxide, and some carbon dioxide. In partial oxidation the fuel is combusted with a sub-stoichiometric quantity of oxygen. Steam reforming uses water to reform the fuel, is highly endothermic and requires a significant heat input, usually provided by combusting some amount of the...

Chemical Engineering Journal, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Applied Catalysis B: Environmental, 2021

Abstract We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a... more Abstract We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a reducible, mesoporous TiO2 nanosphere to enhance thermal stability and catalytic activity for VOC oxidation. Through comparisons with surface-impregnated Ag-TiO2, which suffer from significant sintering and deactivation after aging at 550 °C, we show that encapsulation helps maintain a uniform Ag particle distribution (2−5 nm) and promotes metal-support interactions by maximizing interfacial sites, thereby improving activity and stability. In addition, we discover that subjecting the encapsulated catalyst to a post-synthesis solvothermal treatment step anchors the active metal more strongly to the support, which helps maintain superior activity under repeated aging cycles. Finally, recognizing that industrial flue gas streams inevitably contain water vapor we examine a constructive method of deliberately exposing the catalyst’s surface to water vapor before beginning the reaction. This simple method enhances the rate of VOC oxidation up to six-fold at temperatures as low as 40 °C.

Applied Catalysis B: Environmental, 2021

Understanding the chemistry during the preparation of Pd/SSZ-13 for the low-temperature NO adsorp... more Understanding the chemistry during the preparation of Pd/SSZ-13 for the low-temperature NO adsorption: The role of NH 4-SSZ-13 support Huawang Zhao (Investigation) (Writing-original draft), Xiaoyin Chen (Methodology), Adarsh Bhat (Investigation), Yongdan Li (Conceptualization), Johannes W. Schwank (Supervision) (Writingreview and editing) (Project administration

Catalysis Communications, 2018

Maintaining high dispersion of palladium is critical for Pd-based catalysts, which suffer from de... more Maintaining high dispersion of palladium is critical for Pd-based catalysts, which suffer from deactivation due to sintering at high temperatures (≥800°C). Here, we report direct evidence that Pd nanoparticles (~4 nm) of a palladium silica core@shell (Pd@SiO 2) catalyst can redisperse into nanoclusters (≤2 nm) after aging at 800°C, where severe Pd sintering would be expected on supported Pd catalysts. The Pd redispersion was confirmed by in situ, as well as ex situ, high resolution transmission electron microscopy, and is manifested by a remarkably decreased light-off temperature for CO oxidation after aging.

Catalysis Today, 2019

This is an electronic reprint of the original article. This reprint may differ from the original ... more This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.

Catalysis Science & Technology, 2019

The catalytic activity is enhanced by Ce but inhibited by La dopant. The catalysts have been char... more The catalytic activity is enhanced by Ce but inhibited by La dopant. The catalysts have been characterized in light of structural properties, reducibility, mobility of adsorbed oxygen and lattice oxygen, and surface reaction intermediates.

Catalysis Today, 2018

CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage ... more CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage and release. This unique feature, which is usually referred to as "oxygen storage capacity" (OSC), can be quantitatively evaluated by different methods and techniques. Since the oxygen release benefits oxidation reactions, catalytic activity can be correlated with OSC. The measured amount of OSC can be influenced by a number of factors, such as the nature of the reducing agent, the conditions of reducing gas flow and operation temperature, the aging, the composition, and physical and geometric properties of CeO 2-based materials, and the type of analytical technique used. Therefore, these influencing factors include, but are not limited to, the use of H 2 or CO as reducing agent, continuous or pulsed feed of reducing agent, the presence of other elements in the CeO 2 structure, particle size and surface area, supported catalyst components and aging, etc. This review paper focuses on the measurement of OSC, the effect of influencing factors, and the role of OSC in the typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions. Furthermore, this review addresses the reactions in which the catalytic activity can be correlated with OSC.

Applied Catalysis B: Environmental, 2018

Abstract Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust c... more Abstract Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust control. It is a challenge to improve performance and reduce the cost of DOCs, while also to avoid interference of hydrocarbons and sintering of platinum metals at high temperatures. We present here an indium-doped Co 3 O 4 uniform nanorod catalyst whose catalytic performance in CO, C 3 H 6 , and even NO oxidation is comparable to platinum-group DOCs in diesel exhaust. No obvious deactivation was observed in long-term stability tests under simulated diesel exhaust conditions. These indium-doped Co 3 O 4 nanorods might open a promising pathway towards low-cost efficient diesel exhaust control systems. Characterization results indicated that lattice oxygen could be much more easily abstracted by hydrogen or carbon monoxide from indium-doped Co 3 O 4 than from Co 3 O 4 and the physical mixture Co 3 O 4 and In 2 O 3 . The presence of indium with its large cation radius could influence the chemical status of surface/chemisorbed oxygen in Co 3 O 4 -In 2 O 3 nanorods, thereby increasing the mobility of lattice oxygen involved in the catalytic oxidation reaction. The reaction mechanism of catalytic oxidation of CO and C 3 H 6 were evaluated based on kinetic and FTIR studies. For CO oxidation, activated CO 3 * reduced by adsorbed CO* in an irreversible step to generate the final product of CO 2 could be considered as the kinetically-relevant step. DRIFT spectroscopy confirmed that only stable carbonate species were observed over Co 3 O 4 -In 2 O 3 nanorods that might be further reduced by CO to form CO 2 . For C 3 H 6 oxidation, the incorporation of activated oxygen (O*) into anion vacancy of catalyst surface was the kinetically-relevant step, while the active sites on catalyst surface should be totally covered by the intermediates of C 3 H 6 or its generated species, which actually acted as the most abundant surface intermediates (MASI). DRIFT spectroscopy confirmed that C 3 H 6 and its related intermediates like formate, acetate, and acetone species would be formed over Co 3 O 4 -In 2 O 3 nanorods.

Applied Catalysis B: Environmental, 2017

Nano-sized noble metal particles are an essential component in automotive catalytic converters. H... more Nano-sized noble metal particles are an essential component in automotive catalytic converters. However, during customer in-use operation they agglomerate into larger particles and the performance of the catalytic converter is negatively affected. Engine control methods are needed to provide an environment capable of redispersing noble metal catalyst particles while the particle size is still small. In this study, Pd model powder catalysts, supported on three-way catalytic converter washcoat components of ceria-zirconia (Pd/CZO), 4wt% La2O3 stabilized γ-Al2O3 (Pd/Al) and unstabilized γ-Al2O3 (Pd/A) were exposed to redox cycling at 700°C for 16 hours (to simulate customer in-use operation engine exhaust) either continuously or interrupted with brief air pulses. The two goals of this research were to determine the air pulse length required so that any Pd redispersion gains achieved by air treatment in each 20 minute redox cycle will be retained by the end of the 16 hour aging, and to determine if these supports enable rapid Pd redispersion on the time scale of a common ~10 second engine fuel cut. Pd particle size and dispersion measurements were performed with three complimentary techniques of H2 chemisorption, XRD and electron microscopy since not one technique could be used exclusively. Catalyst activity was determined by CO oxidation with the Water Gas Shift (WGS) reaction and Oxygen Storage Capacity (OSC) measurements to probe the contact between the noble metal and support at a given state of catalyst deterioration, and a CO light-off test to confirm trends

Chemical Microsensors and Applications II, 1999

ABSTRACT

Journal of Thermal Analysis, 1987

Bimetallic Ru~u samples supported on SiO 2, AI203 and MgO were studied by the temperature-program... more Bimetallic Ru~u samples supported on SiO 2, AI203 and MgO were studied by the temperature-programmed reduction (TPR) technique. Experiments were carried out both on unreduced impregnated salts and after oxidation of already reduced samples. The TPR profiles reveal a simultaneous reduction of ruthenium and copper precursors, even though the Ru and Cu in the monometallic catalysts exhibit reduction peaks which differ by up to 150 ~ It is suggested that the two metal salts interact during the stages of preparation and drying, and after reduction form bimetallic aggregates which are not stable and tend to separate. The stability of the bimetallic particles was found to be strongly dependent on the support used, being higher on SiO 2 than on A1203 and MgO. It is suggested that the chemical nature of the support determines the different degree of interaction and/or agglomeration of the bimetallic particles.

Journal of Catalysis, 1986

The catalytic properties for the hydrogenolysis of ethane, propane, and cyclopropane of a series ... more The catalytic properties for the hydrogenolysis of ethane, propane, and cyclopropane of a series of highly dispersed RuNaY catalysts have been investigated. These catalysts have activities and selectivities for ethane and propane hydrogenolysis similar to other supported ruthenium catalysts. However, the activity of the RuNaY for cyclopropane hydrogenolysis is much higher than that of Ru on conventional oxide supports, while the selectivities remain in a range expected for welldispersed ruthenium. The increase in activity for the RuNaY catalysts is due mainly to the presence of highly dispersed Ru particles made possible by the zeolite support. A destabilization of the cyclopropane ring by the electrostatic field of the zeolite, however, does not seem to contribute significantly to the observed rate increase. It appears that the ring opening of cyclopropane and the hydrogenolysis of cyclopropane to ethane and methane have a common intermediate, the formation of which is rate determining for both reactions. The discovery that on Ru the ring opening of cyclopropane is structure sensitive is surprising since this reaction is generally considered as a classic example for structure insensitivity. 0 ,986 Academy P'res~, Inc

Journal of Catalysis, 1981

Ru-Au catalysts supported on SiO, were characterized by using H, and O2 chemisorption, wideangle ... more Ru-Au catalysts supported on SiO, were characterized by using H, and O2 chemisorption, wideangle X-ray scattering, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Catalytic activity was measured for the hydrogenolysis of propane and ethane. The hydrogenolysis activity of ruthenium decreased by two orders of magnitude with addition of gold. This suggested that Ru and Au did not exist as separate particles but formed bimetallic aggregates. Chemisorption and XPS experiments showed a surface composition similar to the bulk. A comparison was made with a previously studied Ru-Au-on-MgO system, on which an enrichment of Ru on the surface of bimetallic Ru-Au clusters was discovered. It is suggested that the strength of the metal-support interaction can affect the surface composition of multimetallic supported systems. 283

Journal of Catalysis, 1980

The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold cat... more The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold catalysts. The results on supported ruthenium are similar to those on Ruq. The exchange reaction seems to be unaffected by differences in particle size or nature of the support (MgO or Siq, respectively). The heterogeneous exchange kinetics deviate from an exponential law. This indicates the presence of nonuniformities on the catalyst surface and/or a contribution of oxygen diffusion. On supported gold, high exchange activity and massive uptake of labeled oxygen by the solid phase are observed. Au/MgO is one order of magnitude more active than Au/SiOZ. The activation of support oxygen for the isotopic exchange reaction is related to an interaction between gold and support.

Journal of Catalysis, 1992

A series of Pt-Sn/A1203 catalysts supported on Degussa nonporous alumina were characterized by in... more A series of Pt-Sn/A1203 catalysts supported on Degussa nonporous alumina were characterized by infrared spectroscopy of adsorbed CO. The nominal platinum loading was kept constant in the catalysts at l wt% and the nominal amount of tin was varied from 0 to 5 wt%. At room temperature it was found that there was a general trend for the linearly adsorbed CO band to shift to lower frequencies with increasing amounts of tin in the catalyst, except for one of the catalysts (1.0 Pt-1.0 Sn/AI203) where a particle size effect seemed to be dominant. The amount of bridge-bonded CO species was very small and became undetectable in the case of large tin loadings (1 and 5 wt% Sn). Thermal desorption infrared spectroscopy was used to determine the vibration frequency of the isolated CO molecule and hence observe if there were any indications of electronic interactions between tin and platinum. For the monometallic 1.0 Pt/A1203 sample the singleton vibration frequency was 2041 cm-t. For all the Pt-Sn bimetallic samples it was found that the singleton vibration frequency lay within the range 2041-+ 6 cm-1. This suggests that the electronic effect of Sn on Pt in our Pt-Sn/A120 3 catalysts is not very large.

Frontiers of Chemical Science and Engineering, 2017

A significant portion of the world’s population does not have access to safe drinking water. This... more A significant portion of the world’s population does not have access to safe drinking water. This problem is most acute in remote, resource-constrained rural settings in developing countries. Water filtration using activated carbon is one of the important steps in treating contaminated water. Lignocellulosic biomass is generally available in abundance in such locations, such as the African rain forests. Our work is focused on developing a simple method to synthesize activated biochar from locally available materials. The preparation of activated biochar with diammonium hydrogenphosphate (DAP) as the activating agent is explored under N2 flow and air. The study, carried out with cellulose as a model biomass, provides some insight into the interaction between DAP and biomass, as well as the char forming mechanism. Various characterization techniques such as N2 physisorption, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy are utilized to compare the properties between biochar formed under nitrogen and partial oxidative conditions. At a temperature of 450 °C, the loading of DAP over cellulose is systematically varied, and its effect on activation is examined. The activated biochar samples are predominantly microporous in the range of concentrations studied. The interaction of DAP with cellulose is investigated and the nature of bonding of the heteroatoms to the carbonaceous matrix is elucidated. The results indicate that the quality of biochar prepared under partial oxidation condition is comparable to that of biochar prepared under nitrogen, leading to the possibility of an activated biochar production scheme on a small scale in resource-constrained settings.

Introduction Fuel cells, which produce electricity directly from hydrogen and oxygen, offer a cle... more Introduction Fuel cells, which produce electricity directly from hydrogen and oxygen, offer a clean and efficient potential alternative to internal combustion engines for generating power for portable and transportation applications. However, there currently is no infrastructure for the wide scale production and distribution of hydrogen to the transportation market. Instead of building new infrastructure, it is possible to produce hydrogen on-demand from common hydrocarbon fuels. [1] Several catalytic processes can be used to produce hydrogen from hydrocarbons. The most common are partial oxidation (POX), steam reforming (SR), and autothermal reforming (ATR), all of which produce primarily hydrogen, carbon monoxide, and some carbon dioxide. In partial oxidation the fuel is combusted with a sub-stoichiometric quantity of oxygen. Steam reforming uses water to reform the fuel, is highly endothermic and requires a significant heat input, usually provided by combusting some amount of the...

Chemical Engineering Journal, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Applied Catalysis B: Environmental, 2021

Abstract We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a... more Abstract We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a reducible, mesoporous TiO2 nanosphere to enhance thermal stability and catalytic activity for VOC oxidation. Through comparisons with surface-impregnated Ag-TiO2, which suffer from significant sintering and deactivation after aging at 550 °C, we show that encapsulation helps maintain a uniform Ag particle distribution (2−5 nm) and promotes metal-support interactions by maximizing interfacial sites, thereby improving activity and stability. In addition, we discover that subjecting the encapsulated catalyst to a post-synthesis solvothermal treatment step anchors the active metal more strongly to the support, which helps maintain superior activity under repeated aging cycles. Finally, recognizing that industrial flue gas streams inevitably contain water vapor we examine a constructive method of deliberately exposing the catalyst’s surface to water vapor before beginning the reaction. This simple method enhances the rate of VOC oxidation up to six-fold at temperatures as low as 40 °C.

Applied Catalysis B: Environmental, 2021

Understanding the chemistry during the preparation of Pd/SSZ-13 for the low-temperature NO adsorp... more Understanding the chemistry during the preparation of Pd/SSZ-13 for the low-temperature NO adsorption: The role of NH 4-SSZ-13 support Huawang Zhao (Investigation) (Writing-original draft), Xiaoyin Chen (Methodology), Adarsh Bhat (Investigation), Yongdan Li (Conceptualization), Johannes W. Schwank (Supervision) (Writingreview and editing) (Project administration

Catalysis Communications, 2018

Maintaining high dispersion of palladium is critical for Pd-based catalysts, which suffer from de... more Maintaining high dispersion of palladium is critical for Pd-based catalysts, which suffer from deactivation due to sintering at high temperatures (≥800°C). Here, we report direct evidence that Pd nanoparticles (~4 nm) of a palladium silica core@shell (Pd@SiO 2) catalyst can redisperse into nanoclusters (≤2 nm) after aging at 800°C, where severe Pd sintering would be expected on supported Pd catalysts. The Pd redispersion was confirmed by in situ, as well as ex situ, high resolution transmission electron microscopy, and is manifested by a remarkably decreased light-off temperature for CO oxidation after aging.

Catalysis Today, 2019

This is an electronic reprint of the original article. This reprint may differ from the original ... more This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.

Catalysis Science & Technology, 2019

The catalytic activity is enhanced by Ce but inhibited by La dopant. The catalysts have been char... more The catalytic activity is enhanced by Ce but inhibited by La dopant. The catalysts have been characterized in light of structural properties, reducibility, mobility of adsorbed oxygen and lattice oxygen, and surface reaction intermediates.

Catalysis Today, 2018

CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage ... more CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage and release. This unique feature, which is usually referred to as "oxygen storage capacity" (OSC), can be quantitatively evaluated by different methods and techniques. Since the oxygen release benefits oxidation reactions, catalytic activity can be correlated with OSC. The measured amount of OSC can be influenced by a number of factors, such as the nature of the reducing agent, the conditions of reducing gas flow and operation temperature, the aging, the composition, and physical and geometric properties of CeO 2-based materials, and the type of analytical technique used. Therefore, these influencing factors include, but are not limited to, the use of H 2 or CO as reducing agent, continuous or pulsed feed of reducing agent, the presence of other elements in the CeO 2 structure, particle size and surface area, supported catalyst components and aging, etc. This review paper focuses on the measurement of OSC, the effect of influencing factors, and the role of OSC in the typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions. Furthermore, this review addresses the reactions in which the catalytic activity can be correlated with OSC.

Applied Catalysis B: Environmental, 2018

Abstract Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust c... more Abstract Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust control. It is a challenge to improve performance and reduce the cost of DOCs, while also to avoid interference of hydrocarbons and sintering of platinum metals at high temperatures. We present here an indium-doped Co 3 O 4 uniform nanorod catalyst whose catalytic performance in CO, C 3 H 6 , and even NO oxidation is comparable to platinum-group DOCs in diesel exhaust. No obvious deactivation was observed in long-term stability tests under simulated diesel exhaust conditions. These indium-doped Co 3 O 4 nanorods might open a promising pathway towards low-cost efficient diesel exhaust control systems. Characterization results indicated that lattice oxygen could be much more easily abstracted by hydrogen or carbon monoxide from indium-doped Co 3 O 4 than from Co 3 O 4 and the physical mixture Co 3 O 4 and In 2 O 3 . The presence of indium with its large cation radius could influence the chemical status of surface/chemisorbed oxygen in Co 3 O 4 -In 2 O 3 nanorods, thereby increasing the mobility of lattice oxygen involved in the catalytic oxidation reaction. The reaction mechanism of catalytic oxidation of CO and C 3 H 6 were evaluated based on kinetic and FTIR studies. For CO oxidation, activated CO 3 * reduced by adsorbed CO* in an irreversible step to generate the final product of CO 2 could be considered as the kinetically-relevant step. DRIFT spectroscopy confirmed that only stable carbonate species were observed over Co 3 O 4 -In 2 O 3 nanorods that might be further reduced by CO to form CO 2 . For C 3 H 6 oxidation, the incorporation of activated oxygen (O*) into anion vacancy of catalyst surface was the kinetically-relevant step, while the active sites on catalyst surface should be totally covered by the intermediates of C 3 H 6 or its generated species, which actually acted as the most abundant surface intermediates (MASI). DRIFT spectroscopy confirmed that C 3 H 6 and its related intermediates like formate, acetate, and acetone species would be formed over Co 3 O 4 -In 2 O 3 nanorods.

Applied Catalysis B: Environmental, 2017

Nano-sized noble metal particles are an essential component in automotive catalytic converters. H... more Nano-sized noble metal particles are an essential component in automotive catalytic converters. However, during customer in-use operation they agglomerate into larger particles and the performance of the catalytic converter is negatively affected. Engine control methods are needed to provide an environment capable of redispersing noble metal catalyst particles while the particle size is still small. In this study, Pd model powder catalysts, supported on three-way catalytic converter washcoat components of ceria-zirconia (Pd/CZO), 4wt% La2O3 stabilized γ-Al2O3 (Pd/Al) and unstabilized γ-Al2O3 (Pd/A) were exposed to redox cycling at 700°C for 16 hours (to simulate customer in-use operation engine exhaust) either continuously or interrupted with brief air pulses. The two goals of this research were to determine the air pulse length required so that any Pd redispersion gains achieved by air treatment in each 20 minute redox cycle will be retained by the end of the 16 hour aging, and to determine if these supports enable rapid Pd redispersion on the time scale of a common ~10 second engine fuel cut. Pd particle size and dispersion measurements were performed with three complimentary techniques of H2 chemisorption, XRD and electron microscopy since not one technique could be used exclusively. Catalyst activity was determined by CO oxidation with the Water Gas Shift (WGS) reaction and Oxygen Storage Capacity (OSC) measurements to probe the contact between the noble metal and support at a given state of catalyst deterioration, and a CO light-off test to confirm trends

Chemical Microsensors and Applications II, 1999

ABSTRACT

Journal of Thermal Analysis, 1987

Bimetallic Ru~u samples supported on SiO 2, AI203 and MgO were studied by the temperature-program... more Bimetallic Ru~u samples supported on SiO 2, AI203 and MgO were studied by the temperature-programmed reduction (TPR) technique. Experiments were carried out both on unreduced impregnated salts and after oxidation of already reduced samples. The TPR profiles reveal a simultaneous reduction of ruthenium and copper precursors, even though the Ru and Cu in the monometallic catalysts exhibit reduction peaks which differ by up to 150 ~ It is suggested that the two metal salts interact during the stages of preparation and drying, and after reduction form bimetallic aggregates which are not stable and tend to separate. The stability of the bimetallic particles was found to be strongly dependent on the support used, being higher on SiO 2 than on A1203 and MgO. It is suggested that the chemical nature of the support determines the different degree of interaction and/or agglomeration of the bimetallic particles.

Journal of Catalysis, 1986

The catalytic properties for the hydrogenolysis of ethane, propane, and cyclopropane of a series ... more The catalytic properties for the hydrogenolysis of ethane, propane, and cyclopropane of a series of highly dispersed RuNaY catalysts have been investigated. These catalysts have activities and selectivities for ethane and propane hydrogenolysis similar to other supported ruthenium catalysts. However, the activity of the RuNaY for cyclopropane hydrogenolysis is much higher than that of Ru on conventional oxide supports, while the selectivities remain in a range expected for welldispersed ruthenium. The increase in activity for the RuNaY catalysts is due mainly to the presence of highly dispersed Ru particles made possible by the zeolite support. A destabilization of the cyclopropane ring by the electrostatic field of the zeolite, however, does not seem to contribute significantly to the observed rate increase. It appears that the ring opening of cyclopropane and the hydrogenolysis of cyclopropane to ethane and methane have a common intermediate, the formation of which is rate determining for both reactions. The discovery that on Ru the ring opening of cyclopropane is structure sensitive is surprising since this reaction is generally considered as a classic example for structure insensitivity. 0 ,986 Academy P'res~, Inc

Journal of Catalysis, 1981

Ru-Au catalysts supported on SiO, were characterized by using H, and O2 chemisorption, wideangle ... more Ru-Au catalysts supported on SiO, were characterized by using H, and O2 chemisorption, wideangle X-ray scattering, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Catalytic activity was measured for the hydrogenolysis of propane and ethane. The hydrogenolysis activity of ruthenium decreased by two orders of magnitude with addition of gold. This suggested that Ru and Au did not exist as separate particles but formed bimetallic aggregates. Chemisorption and XPS experiments showed a surface composition similar to the bulk. A comparison was made with a previously studied Ru-Au-on-MgO system, on which an enrichment of Ru on the surface of bimetallic Ru-Au clusters was discovered. It is suggested that the strength of the metal-support interaction can affect the surface composition of multimetallic supported systems. 283

Journal of Catalysis, 1980

The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold cat... more The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold catalysts. The results on supported ruthenium are similar to those on Ruq. The exchange reaction seems to be unaffected by differences in particle size or nature of the support (MgO or Siq, respectively). The heterogeneous exchange kinetics deviate from an exponential law. This indicates the presence of nonuniformities on the catalyst surface and/or a contribution of oxygen diffusion. On supported gold, high exchange activity and massive uptake of labeled oxygen by the solid phase are observed. Au/MgO is one order of magnitude more active than Au/SiOZ. The activation of support oxygen for the isotopic exchange reaction is related to an interaction between gold and support.