TY - JOUR
T1 - Kinetics and mechanism of ethylene hydrogenation poisoned by CO on silica-supported monodisperse Pt nanoparticles
AU - Rioux, Robert M.
AU - Komor, Russell
AU - Song, Hyunjoon
AU - Hoefelmeyer, James D.
AU - Grass, Michael
AU - Niesz, Krisztian
AU - Yang, Peidong
AU - Somorjai, Gabor A.
N1 - Funding Information:
This work was supported by the Director, Office of Science, Office of Advanced Scientific Computing Research, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the U.S. Department of Energy under contract DE-AC02-05CH11231. The authors thank Professor M.A. Vannice, Pennsylvania State University for donating the 3.2% Pt/SiO 2 catalyst and Dr. Samrat Mukherjee for its preparation. They also thank the Exxon Research and Developmental Laboratory for donating the Pt/Al 2 O 3 sample. R.M.R. thanks the Ford Motor Company for financial support through a graduate fellowship administered by the Berkeley Catalysis Center.
PY - 2008/2/15
Y1 - 2008/2/15
N2 - The influence of particle size on the poisoning of ethylene hydrogenation by CO was studied over a series of catalysts composed of nearly monodisperse Pt nanoparticles (1.7-7.1 nm) encapsulated in mesoporous silica (SBA-15). The turnover frequency at 403 K in the presence of 0.5 Torr CO was ∼2 × 10-2 s-1 (compared with ∼102 s-1 in the absence of CO). The apparent activation energy in the absence and presence of 0.2 Torr CO was ∼10 and 20 kcal mol-1, respectively. The pressure dependency changes significantly in the presence of CO; reaction orders in hydrogen were 1/2 in the presence of CO at 403 K and noncompetitive with regard to co-adsorption with C2H4. In the absence of CO at similar temperatures, H2 adsorption was primarily irreversible (first-order dependence), and H2 and C2H4 compete for the same sites. Ethylene orders at 403 K were first order in the presence of 0.2 Torr CO and remained unity with increasing CO pressure. At similar reaction conditions in the absence of CO, ethylene had an inhibitory effect (negative reaction order) on the overall hydrogenation reaction. The change in C2H4 and H2 kinetics suggests strong competitive adsorption between C2H4 and CO for the same type of site, whereas H2 apparently adsorbs on distinct surface sites due either to steric hindrance or H2-induced CO desorption. Incorporation of a quasi-equilibrated CO adsorption step into a noncompetitive Langmuir-Hinshelwood mechanism predicts the experimentally observed pressure dependencies and a doubling of the apparent activation energy. Hydrogenation of ethylene in the presence of 1 Torr CO was examined under reaction conditions at 403 K by infrared spectroscopy; the only surface species identified under reaction conditions was linear-bound CO. The hydrogenation of ethylene on clean Pt catalysts was structure-insensitive and remains insensitive in the presence of CO; rates decreased only by a factor of two with increasing particle size.
AB - The influence of particle size on the poisoning of ethylene hydrogenation by CO was studied over a series of catalysts composed of nearly monodisperse Pt nanoparticles (1.7-7.1 nm) encapsulated in mesoporous silica (SBA-15). The turnover frequency at 403 K in the presence of 0.5 Torr CO was ∼2 × 10-2 s-1 (compared with ∼102 s-1 in the absence of CO). The apparent activation energy in the absence and presence of 0.2 Torr CO was ∼10 and 20 kcal mol-1, respectively. The pressure dependency changes significantly in the presence of CO; reaction orders in hydrogen were 1/2 in the presence of CO at 403 K and noncompetitive with regard to co-adsorption with C2H4. In the absence of CO at similar temperatures, H2 adsorption was primarily irreversible (first-order dependence), and H2 and C2H4 compete for the same sites. Ethylene orders at 403 K were first order in the presence of 0.2 Torr CO and remained unity with increasing CO pressure. At similar reaction conditions in the absence of CO, ethylene had an inhibitory effect (negative reaction order) on the overall hydrogenation reaction. The change in C2H4 and H2 kinetics suggests strong competitive adsorption between C2H4 and CO for the same type of site, whereas H2 apparently adsorbs on distinct surface sites due either to steric hindrance or H2-induced CO desorption. Incorporation of a quasi-equilibrated CO adsorption step into a noncompetitive Langmuir-Hinshelwood mechanism predicts the experimentally observed pressure dependencies and a doubling of the apparent activation energy. Hydrogenation of ethylene in the presence of 1 Torr CO was examined under reaction conditions at 403 K by infrared spectroscopy; the only surface species identified under reaction conditions was linear-bound CO. The hydrogenation of ethylene on clean Pt catalysts was structure-insensitive and remains insensitive in the presence of CO; rates decreased only by a factor of two with increasing particle size.
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U2 - 10.1016/j.jcat.2007.10.015
DO - 10.1016/j.jcat.2007.10.015
M3 - Article
AN - SCOPUS:38649113247
SN - 0021-9517
VL - 254
SP - 1
EP - 11
JO - Journal of Catalysis
JF - Journal of Catalysis
IS - 1
ER -