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Research paper thumbnail of Catalytic reduction of nitric oxide: studies using ammonia and methane as reducing agents /

Research paper thumbnail of Characterization and Activity of Vanadium Oxide Catalysts in Selective Catalytic Reduction of Nitric Oxide

Studies in Surface Science and Catalysis, 1993

Nitric oxide reduction with ammonia and direct oxidation of ammonia were studied over unsupported... more Nitric oxide reduction with ammonia and direct oxidation of ammonia were studied over unsupported vanadia catalysts, having preferential exposure of different crystal planes. Surface species and morphological factors were investigated by using various characterization techniques. The activity and selectivity measurements were performed using a steady-state fixed-bed reactor system.

Research paper thumbnail of Mechanistic studies of selective catalytic reduction of nitric oxide with ammonia over V2O5/TiO2 (anatase) catalysts through transient isotopic labeling at steady state

The Journal of Physical Chemistry, 1995

Isotopic tracers studies were performed to investigate the reaction network of selective catalyti... more Isotopic tracers studies were performed to investigate the reaction network of selective catalytic reduction (SCR) on vanadia catalysts supported over titania. The catalysts were characterized using BET surface area analysis, X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermal analysis techniques. The product analysis was carried out by a combination of chemiluminescence NO, analysis, gas chromatography-mass spectrometry, and chemical titration methods. The isotopic labeling experiments were performed under steady-state conditions by using 15N-and lSOcontaining species. The results obtained in these experiments were combined with the nitric oxide and oxygen exchange experiments to arrive at conclusions regarding the pathways of the SCR reactions. The role of ammonia oxidation has been quantified in the overall SCR reaction network at higher temperatures.

Research paper thumbnail of Nitric Oxide Reduction with Methane over Pd/TiO2Catalysts

Journal of Catalysis, 1997

Steady-state reaction studies were performed over a Pd/titania catalyst for NO reduction using CH... more Steady-state reaction studies were performed over a Pd/titania catalyst for NO reduction using CH 4 as a reducing agent. The catalyst was prepared using a wet impregnation technique and Pdacetate as a precursor for palladium. Characterization of the catalyst samples was performed using the BET surface area technique, X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermal analysis techniques. A fixed-bed, flow reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were done on-line using gas chromatography-mass spectrometry, chemiluminescence, and wet chemistry techniques. Temperature-programmed reduction studies indicated that the catalyst was reducible by H 2 even at sub-ambient temperatures. The catalyst was seen to reduce NO with conversions above 95% in the oxygen concentration range from 0 to 1.3%. Oscillatory behavior was exhibited by the catalyst under certain reaction conditions. The results obtained from the reaction experiments, together with the findings from the characterization studies, are used to explain the mechanistic aspects of this reaction.

Research paper thumbnail of Investigation of the Reaction Pathways in Selective Catalytic Reduction of NO with NH3 over V2O5 Catalysts: Isotopic Labeling Studies Using 18O2, 15NH3, 15NO, and 15N18O

Journal of Catalysis, 1994

Research paper thumbnail of Investigation of the Mechanism of Ammonia Oxidation and Oxygen Exchange over Vanadia Catalysts Using N-15 and O-18 Tracer Studies

Journal of Catalysis, 1994

Research paper thumbnail of Reaction Pathways in the Selective Catalytic Reduction Process with NO and NO2 at Low Temperatures

Industrial & Engineering Chemistry Research, 2001

The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases c... more The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO 2 was investigated. The two main reactions are 4NH 3 + 2NO + 2NO 2 f 4N 2 + 6H 2 O and 2NH 3 + 2NO 2 f NH 4 NO 3 + N 2 + H 2 O. The "fast SCR reaction" exhibits a reaction rate at least 10 times higher than that of the well-known standard SCR reaction with pure NO and dominates at temperatures above 200°C. At lower temperatures, the "ammonium nitrate route" becomes increasingly important. Under extreme conditions, e.g., a powder catalyst at T ≈ 140°C, the ammonium nitrate route may be responsible for the whole NO x conversion observed. This reaction leads to the formation of ammonium nitrate within the pores of the catalyst and a temporary deactivation. For a typical monolithic sample, the lower threshold temperature at which no degradation of catalyst activity with time is observed is around 180°C. The ammonium nitrate route is interesting from a standpoint of general DeNO x mechanisms: This reaction combines the features typical to the SCR catalyst with the features of the NO x storage-reduction catalyst, i.e., NO x adsorption to a basic site.

Research paper thumbnail of Activity and temperature-programmed adsorption/desorption behavior of PdTiO2 catalysts in NO/CH4 reduction and NO decomposition reactions

Catalysis Today, 1997

Reduction and decomposition of nitric oxide using methane as a reducing agent has been studied in... more Reduction and decomposition of nitric oxide using methane as a reducing agent has been studied in the presence and absence of oxygen over Pd/TiO 2 catalysts. Temperature-programmed adsorption/desorption and reduction/oxidation behavior has been examined. Prereduced catalysts have shown significant reduction as well as decomposition activity. Isotopic labelling studies using 13CH4, 15N180, 15NO, and 180 2 have also been performed to investigate the interaction of NO and methane with the catalytic sites.

Research paper thumbnail of Characterization and temperature-programmed studies over Pd/TiO2 catalysts for NO reduction with methane

Catalysis Today, 1998

Characterization and temperature-programmed studies were performed over Pd/titania catalysts to e... more Characterization and temperature-programmed studies were performed over Pd/titania catalysts to examine their activity in the reduction of NO with methane. The catalyst was prepared using a wet impregnation technique and Pd-acetate was used as a precursor for palladium. Techniques such as BET surface area measurements, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were used for the characterization of the catalyst before and after the reaction. Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were also used to probe the surface to understand its adsorption/desorption characteristics and reducing capabilities. The results obtained from these studies together with the reaction investigations have given some important insight into the functionality of this catalyst.

Research paper thumbnail of Use of isotopic transient techniques in the study of NO reduction reactions

Applied Catalysis A: General, 1997

ABSTRACT

Research paper thumbnail of Self-Sustained Oscillatory Behavior of NO+CH4+O2Reaction over Titania-Supported Pd Catalysts

Journal of Catalysis, 1997

Self-sustained, regular oscillations were observed in NO + CH 4 + O 2 reaction over Pd/TiO 2 cata... more Self-sustained, regular oscillations were observed in NO + CH 4 + O 2 reaction over Pd/TiO 2 catalysts at specific temperatures and oxygen concentrations. The oscillatory behavior was investigated combining NO reduction and methane combustion reaction studies with additional catalyst characterization experiments performed under controlled atmospheres. The catalyst was prepared using a wet impregnation technique with Pd-acetate as the precursor for palladium. A fixed-bed, flow reactor system was used to perform the NO + CH 4 + O 2 and CH 4 + O 2 reaction experiments. Feed and product analyses were done on-line using gas chromatographymass spectrometry, chemiluminescence, and wet chemistry techniques. Additional catalyst characterization was performed using thermal gravimetric analysis and high-temperature, controlledatmosphere X-ray diffraction techniques. Detailed analysis of the oscillatory behavior has indicated that oscillations in the product and reactant profiles are coupled with temperature oscillations in the catalyst. When combined with controlled-atmosphere characterization experiments, these results, which can be reproduced in both NO + CH 4 + O 2 and CH 4 + O 2 systems, suggested that the oscillations are the result of periodic phase change of palladium on the surface. These cyclic phase transformations, in turn, are the result of temperature variations that are caused by the varying levels of exothermicity of the two major reactions, namely NO reduction and CH 4 combustion, that are favored by the metallic and the oxidic sites, respectively.

Research paper thumbnail of Selective Catalytic Reduction of Nitric Oxide over Vanadia/Titania Catalysts: Temperature-Programmed Desorption and Isotopically Labeled Oxygen-Exchange Studies

Industrial & Engineering Chemistry Research, 1994

Temperature-programmed desorption (TPD) and isotopically labeled oxygen-exchange studies were per... more Temperature-programmed desorption (TPD) and isotopically labeled oxygen-exchange studies were performed over titania-supported vanadia catalysts and bare titania support. The catalysts were characterized using BET surface area analysis, X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermal analysis techniques. The TPD experiments were performed over both the catalyst and the bare support using NO and NH[sub 3] as adsorbates. The exchange reactions performed were: [[sup 14]N[sup 16]O] [yields] [[sup 15]N[sup 18]O] and [[sup 16]O[sub 2]] [yields] [[sup 18]O[sub 2]]. Transient experiments which involved step changes such as [NH[sub 3] + O[sub 2]] [yields] [O[sub 2]] were also performed to observed the transient behavior of various products. These results were combined with the earlier work, and conclusions were drawn regarding the adsorption/desorption and exchange characteristics of these catalysts in the SCR reaction.

Research paper thumbnail of Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts

Applied Catalysis A: General, 1993

... of crystal morphology in selective catalytic reduction of nitric oxide over V2Os catalysts Um... more ... of crystal morphology in selective catalytic reduction of nitric oxide over V2Os catalysts Umit S. Ozkan, Yeping Cai and Mahesh W. Kumthekar ... The gas flow-rates were measured and controlled using four mass flow controllers (Tylan model FC-280 ) and a four-channel readout ...

Research paper thumbnail of Catalytic reduction of nitric oxide: studies using ammonia and methane as reducing agents /

Research paper thumbnail of Characterization and Activity of Vanadium Oxide Catalysts in Selective Catalytic Reduction of Nitric Oxide

Studies in Surface Science and Catalysis, 1993

Nitric oxide reduction with ammonia and direct oxidation of ammonia were studied over unsupported... more Nitric oxide reduction with ammonia and direct oxidation of ammonia were studied over unsupported vanadia catalysts, having preferential exposure of different crystal planes. Surface species and morphological factors were investigated by using various characterization techniques. The activity and selectivity measurements were performed using a steady-state fixed-bed reactor system.

Research paper thumbnail of Mechanistic studies of selective catalytic reduction of nitric oxide with ammonia over V2O5/TiO2 (anatase) catalysts through transient isotopic labeling at steady state

The Journal of Physical Chemistry, 1995

Isotopic tracers studies were performed to investigate the reaction network of selective catalyti... more Isotopic tracers studies were performed to investigate the reaction network of selective catalytic reduction (SCR) on vanadia catalysts supported over titania. The catalysts were characterized using BET surface area analysis, X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermal analysis techniques. The product analysis was carried out by a combination of chemiluminescence NO, analysis, gas chromatography-mass spectrometry, and chemical titration methods. The isotopic labeling experiments were performed under steady-state conditions by using 15N-and lSOcontaining species. The results obtained in these experiments were combined with the nitric oxide and oxygen exchange experiments to arrive at conclusions regarding the pathways of the SCR reactions. The role of ammonia oxidation has been quantified in the overall SCR reaction network at higher temperatures.

Research paper thumbnail of Nitric Oxide Reduction with Methane over Pd/TiO2Catalysts

Journal of Catalysis, 1997

Steady-state reaction studies were performed over a Pd/titania catalyst for NO reduction using CH... more Steady-state reaction studies were performed over a Pd/titania catalyst for NO reduction using CH 4 as a reducing agent. The catalyst was prepared using a wet impregnation technique and Pdacetate as a precursor for palladium. Characterization of the catalyst samples was performed using the BET surface area technique, X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermal analysis techniques. A fixed-bed, flow reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were done on-line using gas chromatography-mass spectrometry, chemiluminescence, and wet chemistry techniques. Temperature-programmed reduction studies indicated that the catalyst was reducible by H 2 even at sub-ambient temperatures. The catalyst was seen to reduce NO with conversions above 95% in the oxygen concentration range from 0 to 1.3%. Oscillatory behavior was exhibited by the catalyst under certain reaction conditions. The results obtained from the reaction experiments, together with the findings from the characterization studies, are used to explain the mechanistic aspects of this reaction.

Research paper thumbnail of Investigation of the Reaction Pathways in Selective Catalytic Reduction of NO with NH3 over V2O5 Catalysts: Isotopic Labeling Studies Using 18O2, 15NH3, 15NO, and 15N18O

Journal of Catalysis, 1994

Research paper thumbnail of Investigation of the Mechanism of Ammonia Oxidation and Oxygen Exchange over Vanadia Catalysts Using N-15 and O-18 Tracer Studies

Journal of Catalysis, 1994

Research paper thumbnail of Reaction Pathways in the Selective Catalytic Reduction Process with NO and NO2 at Low Temperatures

Industrial & Engineering Chemistry Research, 2001

The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases c... more The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO 2 was investigated. The two main reactions are 4NH 3 + 2NO + 2NO 2 f 4N 2 + 6H 2 O and 2NH 3 + 2NO 2 f NH 4 NO 3 + N 2 + H 2 O. The "fast SCR reaction" exhibits a reaction rate at least 10 times higher than that of the well-known standard SCR reaction with pure NO and dominates at temperatures above 200°C. At lower temperatures, the "ammonium nitrate route" becomes increasingly important. Under extreme conditions, e.g., a powder catalyst at T ≈ 140°C, the ammonium nitrate route may be responsible for the whole NO x conversion observed. This reaction leads to the formation of ammonium nitrate within the pores of the catalyst and a temporary deactivation. For a typical monolithic sample, the lower threshold temperature at which no degradation of catalyst activity with time is observed is around 180°C. The ammonium nitrate route is interesting from a standpoint of general DeNO x mechanisms: This reaction combines the features typical to the SCR catalyst with the features of the NO x storage-reduction catalyst, i.e., NO x adsorption to a basic site.

Research paper thumbnail of Activity and temperature-programmed adsorption/desorption behavior of PdTiO2 catalysts in NO/CH4 reduction and NO decomposition reactions

Catalysis Today, 1997

Reduction and decomposition of nitric oxide using methane as a reducing agent has been studied in... more Reduction and decomposition of nitric oxide using methane as a reducing agent has been studied in the presence and absence of oxygen over Pd/TiO 2 catalysts. Temperature-programmed adsorption/desorption and reduction/oxidation behavior has been examined. Prereduced catalysts have shown significant reduction as well as decomposition activity. Isotopic labelling studies using 13CH4, 15N180, 15NO, and 180 2 have also been performed to investigate the interaction of NO and methane with the catalytic sites.

Research paper thumbnail of Characterization and temperature-programmed studies over Pd/TiO2 catalysts for NO reduction with methane

Catalysis Today, 1998

Characterization and temperature-programmed studies were performed over Pd/titania catalysts to e... more Characterization and temperature-programmed studies were performed over Pd/titania catalysts to examine their activity in the reduction of NO with methane. The catalyst was prepared using a wet impregnation technique and Pd-acetate was used as a precursor for palladium. Techniques such as BET surface area measurements, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were used for the characterization of the catalyst before and after the reaction. Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were also used to probe the surface to understand its adsorption/desorption characteristics and reducing capabilities. The results obtained from these studies together with the reaction investigations have given some important insight into the functionality of this catalyst.

Research paper thumbnail of Use of isotopic transient techniques in the study of NO reduction reactions

Applied Catalysis A: General, 1997

ABSTRACT

Research paper thumbnail of Self-Sustained Oscillatory Behavior of NO+CH4+O2Reaction over Titania-Supported Pd Catalysts

Journal of Catalysis, 1997

Self-sustained, regular oscillations were observed in NO + CH 4 + O 2 reaction over Pd/TiO 2 cata... more Self-sustained, regular oscillations were observed in NO + CH 4 + O 2 reaction over Pd/TiO 2 catalysts at specific temperatures and oxygen concentrations. The oscillatory behavior was investigated combining NO reduction and methane combustion reaction studies with additional catalyst characterization experiments performed under controlled atmospheres. The catalyst was prepared using a wet impregnation technique with Pd-acetate as the precursor for palladium. A fixed-bed, flow reactor system was used to perform the NO + CH 4 + O 2 and CH 4 + O 2 reaction experiments. Feed and product analyses were done on-line using gas chromatographymass spectrometry, chemiluminescence, and wet chemistry techniques. Additional catalyst characterization was performed using thermal gravimetric analysis and high-temperature, controlledatmosphere X-ray diffraction techniques. Detailed analysis of the oscillatory behavior has indicated that oscillations in the product and reactant profiles are coupled with temperature oscillations in the catalyst. When combined with controlled-atmosphere characterization experiments, these results, which can be reproduced in both NO + CH 4 + O 2 and CH 4 + O 2 systems, suggested that the oscillations are the result of periodic phase change of palladium on the surface. These cyclic phase transformations, in turn, are the result of temperature variations that are caused by the varying levels of exothermicity of the two major reactions, namely NO reduction and CH 4 combustion, that are favored by the metallic and the oxidic sites, respectively.

Research paper thumbnail of Selective Catalytic Reduction of Nitric Oxide over Vanadia/Titania Catalysts: Temperature-Programmed Desorption and Isotopically Labeled Oxygen-Exchange Studies

Industrial & Engineering Chemistry Research, 1994

Temperature-programmed desorption (TPD) and isotopically labeled oxygen-exchange studies were per... more Temperature-programmed desorption (TPD) and isotopically labeled oxygen-exchange studies were performed over titania-supported vanadia catalysts and bare titania support. The catalysts were characterized using BET surface area analysis, X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermal analysis techniques. The TPD experiments were performed over both the catalyst and the bare support using NO and NH[sub 3] as adsorbates. The exchange reactions performed were: [[sup 14]N[sup 16]O] [yields] [[sup 15]N[sup 18]O] and [[sup 16]O[sub 2]] [yields] [[sup 18]O[sub 2]]. Transient experiments which involved step changes such as [NH[sub 3] + O[sub 2]] [yields] [O[sub 2]] were also performed to observed the transient behavior of various products. These results were combined with the earlier work, and conclusions were drawn regarding the adsorption/desorption and exchange characteristics of these catalysts in the SCR reaction.

Research paper thumbnail of Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts

Applied Catalysis A: General, 1993

... of crystal morphology in selective catalytic reduction of nitric oxide over V2Os catalysts Um... more ... of crystal morphology in selective catalytic reduction of nitric oxide over V2Os catalysts Umit S. Ozkan, Yeping Cai and Mahesh W. Kumthekar ... The gas flow-rates were measured and controlled using four mass flow controllers (Tylan model FC-280 ) and a four-channel readout ...