Sehested Jens, Dahl Søren, Jacobsen Joachim, Rostrup-Nielsen Jens R
Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Kgs. Lyngby, Denmark.
J Phys Chem B. 2005 Feb 17;109(6):2432-8. doi: 10.1021/jp040239s.
The CO methanation reaction over nickel was studied at low CO concentrations and at hydrogen pressures slightly above ambient pressure. The kinetics of this reaction is well described by a first-order expression with CO dissociation at the nickel surface as the rate-determining step. At very low CO concentrations, adsorption of CO molecules and H atoms compete for the sites at the surface, whereas the coverage of CO is close to unity at higher CO pressures. The ratio of the equilibrium constants for CO and H atom adsorption, K(CO)/K(H), was obtained from the rate of CO methanation at various CO concentrations. K(H) was determined independently from temperature programmed adsorption/desorption of hydrogen to be K(H) = 7.7 x 10(-4) (bar(-0.5)) exp[43 (kJ/mol)/RT] and hence the equilibrium constants for adsorption of CO molecules may be calculated to be K(CO) = 3 x 10(-7) (bar(-1)) exp[122 (kJ/mol)/RT]. Furthermore, the rate of dissociation of CO at the catalyst surface was determined to be 5 x 10(9) (s(-1)) exp[-96.7 (kJ/mol)/RT] assuming that 5% of the surface nickel atoms are active for CO dissociation. The results are compared to equilibrium and rate constants reported in the literature.
在低CO浓度和略高于环境压力的氢气压力下，研究了镍上的CO甲烷化反应。该反应动力学可用一级表达式很好地描述，其中镍表面的CO解离为速率决定步骤。在非常低的CO浓度下，CO分子和H原子的吸附竞争表面位点，而在较高的CO压力下，CO的覆盖度接近1。通过不同CO浓度下的CO甲烷化速率获得了CO和H原子吸附平衡常数的比值K(CO)/K(H)。通过程序升温脱附独立测定H原子的K(H)为K(H)=7.7×10(-4)(bar(-0.5))exp[43(kJ/mol)/RT]，因此可计算出CO分子吸附的平衡常数为K(CO)=3×10(-7)(bar(-1))exp[122(kJ/mol)/RT]。此外，假设5%的表面镍原子对CO解离有活性，测定了催化剂表面CO解离的速率为5×10(9)(s(-1))exp[-96.7(kJ/mol)/RT]。将结果与文献报道的平衡常数和速率常数进行了比较。
