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OVERALL KINETICS FOR THE CATALYTIC IGNITION OF ETHANE-AIR MIXTURES ON PLATINUM Reaction rate and related properties evaluation. The measurement of the reaction rate for the diffusion regime offers the possibility to compare the experimental results with several relevant properties like the turnover frequency, TOF, the collision frequency of fuel molecules with the catalytic surface, νF and the ratio rR/νF. The turnover frequency was calculated as TOF=rR/ΓPt, using the literature data for the atomic surface density of platinum exposed atoms (ΓPt=2.49 × 10 –5 mol m -2 [12]). The collision frequency of fuel molecules with the catalytic surface was calculated for the stoichiometric ethane-air mixture as [8]: 1 2 ν F = pF ( 2πM F RTw) (4) where pF is the partial pressure of the fuel and MF its molar mass. The results are given in Table 2. Table 2. Reaction rates and associated properties for diffusion control at Tw = 549 K p0 kPa rR (mol m -2 s -1 ) 10 -3 ×TOF (s -1 ) νF (mol m -2 s -1 ) 10 4 ×(rR/νF) 100 0.0765 3.07 193 3.96 70 0.0720 2.89 135 5.33 50 0.0660 2.65 96.5 6.84 30 0.0591 2.37 57.9 10.2 10 0.0348 1.40 19.3 18.0 The TOF values are very large compared with other literature data [8, 10]. A possible explanation is based on the observation that the platinum wire exhibits significant catalytic activity only after heating at temperatures higher than 800 K, when the initially smooth surface becomes coarse with an increased atomic surface density. The ratio rR/νF has very low values, (4-18) ×10 -4 , indicating a reduced efficiency of fuel collisions with the catalyst surface. If these values are corrected for the activation energy factor (of the order 9.6×10 -2 ), very small sticking coefficients are obtained. The data given in Table 2 indicate that the method and the measurements give realistic results for a typical heterogeneous catalytic reaction of combustion. Reaction order evaluation. The measurements at constant temperature of the reaction heat flow rates for a diffusion controlled process and of the induction periods for a kinetically controlled process can be used to evaluate the overall reaction orders using the linear regression analysis of equations (3) and (2). The results are given in Table 3. It can be observed that the overall reaction orders have an approximately constant value of 0.34, without a significant trend. These figures are in agreement with the frequently reported 197
198 OCTAVIAN STAICU, VALENTIN MUNTEANU, DUMITRU OANCEA order nF=1 for alkane-air catalytic combustion and with the recognized inhibitory effect of oxygen in these reactions (nox
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R /(mol m -2 s -1 ) 0.06 0.05 0.04
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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6 PROFESSOR IOAN BÂLDEA AT HIS 70
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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STUDIES ON WO3 THIN FILMS PREPARED
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PREPARATION AND CHARACTERIZATION OF
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32 C. CĂŢĂNAŞ, M. MOGOŞ, D. HO
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34 C. CĂŢĂNAŞ, M. MOGOŞ, D. HO
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C. CĂŢĂNAŞ, M. MOGOŞ, D. HORVA
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38 ANA-MARIA CORMOS, JOZSEF GASPAR,
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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50 EUGEN DARVASI, LADISLAU KÉKEDY-
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MATHEMATICAL MODELING FOR THE CRYST
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STUDY OF THE CHROMATOGRAPHIC RETENT
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LOWER RIM SILYL SUBSTITUTED CALIX[8
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THE INTERACTION OF SILVER NANOPARTI
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OPTIMISATION OF COPPER REMOVAL FROM
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MELINDA-HAYDEE KOVACS, DUMITRU RIST
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IRON DOPED CARBON AEROGEL AS CATALY
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128 ANDRADA MĂICĂNEANU, HOREA BED
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ANDRADA MĂICĂNEANU, HOREA BEDELEA
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CRISTINA MIHALI, GABRIELA OPREA, EL
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Page 203 and 204: EXPERIMENTAL SECTION 210 MARIA ŞTE
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E / mV vs. SCE POTASSIUM-SELECTIVE
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POTASSIUM-SELECTIVE ELECTRODE BASED
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POTASSIUM-SELECTIVE ELECTRODE BASED
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256 CODRUTA VARODI, DELIA GLIGOR, L
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CODRUTA VARODI, DELIA GLIGOR, LEVEN
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PHARMACOKINETIC INTERACTION BETWEEN
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