Impact of potassium on the heats of adsorption of adsorbed CO species on supported Pt particles by using the AEIR method

摘要

The heats of adsorption at several coverages of the linear and bridged CO species (denoted L and B, respectively) adsorbed on the Pt~0 sites of the 2.9 wt% Pt/10% K/Al_2O_3 catalyst are determined using the Adsorption Equilibrium Infrared spectroscopy method. The addition of K on 2.9% Pt/ Al_2O_3 modifies significantly the adsorption of CO on the Pt particles: (a) the ratio L/B is decreased from 8.4 to 1, (b) a new adsorbed CO species is detected with an IR band at 1763 cm~(-1), (c) the heats of adsorption of L and B CO species are significantly altered and the positions of their IR bands are shifted. The heats of adsorption of L CO species are decreased: i.e. 206 and 105 kJ/mol at low coverages on Pt/Al_2O_3 and Pt/K/Al_2O_3 respectively. Two B CO species denoted B1 and B2, with different heats of adsorption are observed on Pt/K/Al_2O_3. The heats of adsorption of B2 CO species (major B CO species) are significantly larger than those measured in the absence of K: i.e. 94 and 160 kJ/mol at low coverages on Pt/ Al_2O_3 and Pt/K/Al_2O_3 respectively, whereas those of B1 CO species (minor species) are similar: 90 kJ/mol at low coverages. These values are consistent with the qualitative High Resolution Electron Energy Loss Spectrometry literature data on Pt(111) modified by potassium.