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Title: Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst

Abstract

The adsorption of HCN on, its catalytic oxidation with 6% O2 over 0.5% Pt/Al2O3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N2O, NO and NO2, and some residual adsorbed N-containing species were oxidized to NO and NO2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 C. Furthermore, the temperature of maximum HCN conversion to N2O is located between 200 and 250 C, while raising the reaction temperature increases the proportion of NOx in the products. The co-feeding of H2O and C3H6 had little, if any effect on the total HCN conversion, but C3H6 addition did increase the conversion to NO and decrease the conversion to NO2, perhaps due to the competing presence of adsorbed fragments of reductive C3H6. Evidence is also presented that introduction of NO and NO2 into the reactant gas mixturemore » resulted in additional reaction pathways between these NOx species and HCN that provide for lean-NOx reduction coincident with HCN oxidation.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
883676
Report Number(s):
PNNL-SA-47073
3589; 6694; VT0401000; TRN: US200701%%360
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Catalysis. B, Environmental, 65(2006):282-290
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; HYDROCYANIC ACID; ADSORPTION; CATALYSTS; OXIDATION; PLATINUM; ALUMINIUM OXIDES; CATALYTIC EFFECTS; NITROUS OXIDE; NITRIC OXIDE; NITROGEN DIOXIDE; ETHANE; HCN; oxidation; desorption; supported Pt catalyst; C3H6; NO; N2O; NO2; NOx; Environmental Molecular Sciences Laboratory

Citation Formats

Zhao, Haibo, Tonkyn, Russell G, Barlow, Stephan E, Koel, Bruce E, and Peden, Charles HF. Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst. United States: N. p., 2006. Web. doi:10.1016/j.apcatb.2006.02.009.
Zhao, Haibo, Tonkyn, Russell G, Barlow, Stephan E, Koel, Bruce E, & Peden, Charles HF. Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst. United States. doi:10.1016/j.apcatb.2006.02.009.
Zhao, Haibo, Tonkyn, Russell G, Barlow, Stephan E, Koel, Bruce E, and Peden, Charles HF. Mon . "Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst". United States. doi:10.1016/j.apcatb.2006.02.009.
@article{osti_883676,
title = {Catalytic oxidation of HCN over a 0.5% Pt/Al2O3 catalyst},
author = {Zhao, Haibo and Tonkyn, Russell G and Barlow, Stephan E and Koel, Bruce E and Peden, Charles HF},
abstractNote = {The adsorption of HCN on, its catalytic oxidation with 6% O2 over 0.5% Pt/Al2O3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N2O, NO and NO2, and some residual adsorbed N-containing species were oxidized to NO and NO2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 C. Furthermore, the temperature of maximum HCN conversion to N2O is located between 200 and 250 C, while raising the reaction temperature increases the proportion of NOx in the products. The co-feeding of H2O and C3H6 had little, if any effect on the total HCN conversion, but C3H6 addition did increase the conversion to NO and decrease the conversion to NO2, perhaps due to the competing presence of adsorbed fragments of reductive C3H6. Evidence is also presented that introduction of NO and NO2 into the reactant gas mixture resulted in additional reaction pathways between these NOx species and HCN that provide for lean-NOx reduction coincident with HCN oxidation.},
doi = {10.1016/j.apcatb.2006.02.009},
journal = {Applied Catalysis. B, Environmental, 65(2006):282-290},
number = ,
volume = ,
place = {United States},
year = {Mon Mar 27 00:00:00 EST 2006},
month = {Mon Mar 27 00:00:00 EST 2006}
}
  • Fractional factorial design was used to determine which factors have significant effects on the HCN (hydrogen cyanide) oxidation reaction over 0.5% Pt/Al?O? under lean conditions. We conclude that the reaction temperature and gas-hourly space velocity (GHSV) have significant effects on the HCN conversion, while no significant effects are caused by the presence of either NO (nitric oxide) or C?H? (propene). A central composite design was used to study the effects of temperature and GHSV on HCN conversion, C?H? conversion and NOx selectivity. Based on a second polynomial equation model, regression analysis was used to study the significance of each variablemore » term and derive equations for each response. Our results show that HCN conversion was significantly affected by temperature (X3), GHSV (X4), a temperature polynomial term (X32), and a temperature and GHSV interaction term (X3X4). HCN conversion decreased with increasing values of GHSV and increased with increasing temperature, up to a transition temperature that depends on the GHSV value. The variables of temperature (X3), GHSV (X4), and the temperature polynomial term (X32) have significant effects on both C?H? conversion and NOx selectivity, but in these two cases the interaction of temperature and GHSV was not significant. Contour plots of HCN conversion, C?H? conversion, and NOx selectivity versus temperature and GHSV were constructed from an analysis of the measured data, and these plots can be utilized to estimate HCN conversion, C?H? conversion, and NOx selectivity over the range of temperatures and GHSV investigated. Optimum catalyst operation is described by high HCN conversion and low NOx selectivity. These results show C and o that the highest HCN conversion was achieved at temperatures above 250 relatively low GHSV values, while low NOx selectivity was best achieved at a C.o temperature of 215« less
  • TiO2- and ?-Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in-situ FTIR after activation at various conditions and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When ?-Al2O3 was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptivemore » properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in-situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive towards H2 than CO. Consequently, Pt/TiO2 shows substantially lower selectivities towards CO oxidation under PROX conditions than Pt/?-Al2O3.« less
  • TiO2- and -Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in situ FTIR spectroscopy after activation at various conditions, and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When {gamma}-Al{sub 2}O{sub 3} was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density onmore » Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive toward H{sub 2} than CO. Consequently, Pt/TiO{sub 2} shows substantially lower selectivities toward CO oxidation under PROX conditions than Pt/{gamma}-Al{sub 2}O{sub 3}.« less
  • Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at 25 ms resolution in the temperature range 323 to 473 K using various H2 flow rates (1 atm total gas pressure). Surface ethyl species (2870 and 1200 cm-1) were detected at all temperatures along with the gas phase ethane product (2954 and 2893 cm-1). The CH3CH2Pt growth was instantaneous on the time scale of 25ms under all experimental conditions. At 323 K, the decay time of surface ethyl (122 + 10 ms) coincides with the rise time of C2H6 (144 + 14 ms).This establishes direct kinetic evidencemore » for surface ethyl as the kinetically relevant intermediate. Such a direct link between the temporal behavior of an observed intermediate and the final product growth in a heterogeneous catalytic system has not been demonstrated before to our knowledge. A fraction (10 percent) of the asymptotic ethane growth at 323 K is prompt, indicating that there are surface ethyl species that react much faster than the majority of the CH3CH2Pt intermediates. The dispersive kinetics is attributed to the varying strength of interaction of the ethyl species with the Pt surface caused by heterogeneity of the surface environment. At 473 K, the majority of ethyl intermediates are hydrogenated prior to the recording of the first time slice (24 ms), and a correspondingly large prompt growth of ethane is observed. The yield and kinetics of the surface ethylidyne are in agreement with the known spectator nature of this species.« less