Dynamical catalytic responses in the reaction of trans-1,2-dichloroethene on Pd(1 1 0)

The adsorption and reaction of trans-1,2-dichloroethene on Pd(1 1 0) has been studied using molecular beam, temperature programmed desorption and infrared spectroscopies. Our data provide a combination of kinetic and structural information, which demonstrates that the catalytic behaviour of the surface shows a complex and dynamic response to both reactant uptake and substrate temperature, affecting the adsorption, decomposition and product evolution pathways. This essentially partitions the reaction phase space into five different behavioural regimes: Regime I, which occurs between 85 and 128 K, in which molecular adsorption occurs; Regime II, existing between 180 and 220 K in which total and partial decomposition of the molecule occurs, with all fragments being stabilised at the surface; Regime III, which occurs at low uptake in the temperature region 250–675 K, leading to decomposition of the molecule with H2 evolution in the gas phase; Regime IV, which comes into operation at high coverages and the temperature range 250–360 K, in which C2H2 and HCl are evolved into the gas phase and; Regime V, in which a steady-state reaction producing HCl occurs, and which, at low coverages, comes into operation at T>675 K, while at high coverages, comes into play at T>390 K. This overall behaviour, in which both the reactivity and selectivity of the system changes, can be rationalised in terms of dynamic alterations in the ability of the Pd(1 1 0) surface to activate C–H and C–Cl bonds, and dynamic modifications in the kinetic barriers to the recombinative desorption of H2 and HCl, as the concentration of reaction products varies at the surface.