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The adsorptive and reactive behaviour of TiO,, SrTiO, and SrO towards methanol have been investigated using temperature-programmed desorption and XPS. TiO, was found to be reduced during the adsorption/desorption process and showed predominantly CH, formation at low coverages. At higher coverages, alternative paths led also to the desorption of CH,OH and HCHO though CH, was the main product desorbed at ca. 500 K. The product pattern indicates that a methoxy is the major surface intermediate. CO and H, were evolved at ca. 600 K, possibly from the decomposition of a formate species, while H,O was desorbed between 300 and 700 K. On SrO the coincident evolution of CO and H, at 580 K, with H, O and CO, being minor products, indicated a formate intermediate as the dominant one on this surface. The product pattern on SrTiO, resembled that on TiO,, although the main product in this case was CH,OH, with CH, being produced in much smaller quantities and only at much higher temperature than on TiO, (620 K). The source of these differences is discussed in terms of the defect chemistry of the surfaces involved.

Theinteraction offormicacid (HCOOH) with Pd(ll0) wasstudiedusing TPO and XPS. At low doses, at an adsorption temperature of 140 K, HCOOH decomposed to yield CO, COa, H2 and H20 during TPD. CO and Hz were evolved in desorption-limited peaks at 470 and 320 K, respectively. The CO and H z 0 desorptions were saturated at very low doses indicating only a small degreeof formate dehydration in such a transient experiment. The CO2 and Hz evolution continued to increase with dose and the CO2 evolved in a decompmition-limited peak a t 237 K a t low doses which broadened to lower temperature with increasing coverage. This dehydrogenation of HCOOH was of first order with an activation energy of 40 kJ mol-'. At doses above 0.5 L molecularly chemisorbed HCOOH was observed to desorb at 210 K and at still higher doses physisorbed multilayers were present and desorbed a t 180 K. XPS confvmed the presence of CO above 250 K and formate below this temperature. When oxygen was pre-dosed the formate was significantly stabilized and its coverage increased, the CO desorption was removed and Ha was produced a t higher temperatures a t the expense of the H2 peak at 320 K.

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