Postulate of a Mechanism for Temperature Programmed Reaction Spectroscopy (TPRS) Which Accounts for the Coincident Evolution of H2 and CO2 in the TPRS of Succinates and Formates Adsorbed on Cu: Description of a Novel Method for the Identification of the Surface Morphology of Cu on Supported Cu Catalysts

Abstract

The combination of temperature programmed reaction spectroscopy, temperature programmed oxidation (TPO) and N 2 O reactive frontal chromatography (N 2 O-RFC) has shown that the adsorbate produced by dosing dimethylsuccinate on to a Cu/Al 2 O 3 catalyst is a succinate species with 8 out of 10 surface Cu atoms having a succinate species adsorbed on them. The succinate species are bonded end-on and unidentate to the Cu atoms. This configuration constitutes a self-assembled monolayer. Temperature programming causes vicinal strands of the adsorbed succinate to interact, resulting in simultaneous dehydrogenation and decarboxylation, producing coincident evolution of H 2 and CO 2 in peaks at 668 and 793 K and leaving the C of the succinate chain on the Cu surface This C is removed by TPO, producing CO 2 at a peak maximum temperature of 593 K. Prior to the oxidation of the C to CO 2 , TPO oxidises the Cu metal to CuO in the temperature range 323-493 K. Reduction of this CuO produces Cu metal whose metal surface area as measured by N 2 O-RFC is 9.8 m 2 g -1 , a value which is identical to that of the fresh Cu/Al 2 O 3 catalyst. Therefore oxidation of the Cu metal to bulk CuO and re-reduction does not cause sintering of the Cu. However, the surface morphology of the Cu metal produced by reduction of the CuO has changed as evidenced by temperature programmed reduction (TPR)

Evidence for support effects in metal oxide supported cobalt catalysts

“…This is considered to be the rate determining step for the HCO 2 Cu system. Here, however, since we have dosed formic acid on to saturation coverage, it is possible that the decomposition mechanism is the interaction between vicinal adsorbed formate species as we have described previously [15]. The selectivity to CO(S CO ), i.e.…”

“…Temperature programming was then begun at 5 °C min −1 from 30 to 530 °C following H 2 , H 2 O, CO, CO 2 , HCO 2 H and m/z = 29, 31, 32 continuously on the mass spectrometer. Where there is coincident desorption of two or more species, by the tenets of temperature programmed reaction spectroscopy, these derive from the desorption/decomposition of a common intermediate or, as has been recently suggested, by the interaction of vicinal adsorbates [15]. (For full detail of experimental techniques refer to Ref.…”

“…(For full detail of experimental techniques refer to Ref. [15].) The dosage of HCO 2 H corresponding to a partial pressure of 3.38% for 20 min is 3.1 × 10 10 L. The partial pressure of 3.8% atmospheres is insufficient to produce multilayer adsorption but the high dosage will ensure saturation coverage of the adsorbent with the HCO 2 H at the adsorption temperature of 90 °C.…”