The temperature-programmed desorption of hydrogen from copper surfaces

The desorption kinetics of H-2 from a Cu/ZnO/Al2O3 catalyst for methanol sy nthesis were studied under atmospheric pressure in a microreactor set-up by performing temperature-programmed desorption (TPD) experiments after vario us pretreatments of the catalyst. Complete saturation with adsorbed atomic hydrogen was obtained by dosing highly purified H-2 for 1 h at 240 K and at a pressure of 15 bar. The TPD spectra showed symmetric H-2 peaks centered at around 300 K caused by associative desorption of H-2 from Cu metal surfa ce sites. H-2 TPD experiments performed with different initial coverages re sulted in peak maxima shifting to higher temperatures with lower initial co verages indicating that the desorption of H-2 from Cu is of second order. T he microkinetic analysis of the TPD traces obtained with different heating rates yielded an activation energy of desorption of 78 kJmol(-1) and a corr esponding frequency factor of desorption of 3x 10(11) s(-1) in good agreeme nt with the kinetic parameters obtained with Cu(111) under UHV conditions.