Abstract
Exchange reaction of D2O and H2 giving D2 (D2O+H2→H2O+D2) was performed via redox reaction of Cu(O)⇄Cu( ) on Cu/SiO2 catalyst which shows activity for water gas shift (WGS, CO+H2O→CO2+H2) reaction. It was suggested by means of temperature–programmed reduction(TPR) measurement that reduction of CuO to Cu on SiO2 support was occurred around 275°C which was agreeable with values reported in references. Therefore it was deduced that the reduction process is conducted to the catalyst precursors (prec–CuO/SiO2) over the temperature where the active sites of Cu( ) generate on SiO2 support to promote the following exchange reaction. However the exchange reaction proceeded sufficiently at 150 °C on the Cu/SiO2 catalyst at which the initiation step was carried out. Therefore, experiments were carefully carried out on the process to form the active site (Cu( )/SiO2) from prec–CuO/SiO2 in initiation step, regeneration of Cu( )/SiO2 from Cu(O)/SiO2 in the exchange reaction, measurements of the exchange reaction rate on the Cu/SiO2 to which the initial activation steps were made at various temperatures, and measurement of apparent activation energy regarding the reduction of prec–CuO/SiO2. Both the initiation step to form Cu( )/SiO2 from CuO/SiO2 and the regeneration step giving Cu( )/SiO2 from Cu(O)/SiO2 proceeded at a temperature less than 275°C. Apparent activation energy (Eact) of the reduction of CuO/SiO2 was measured by means of closed circulating apparatus, and as a result, Eact was estimated around 56.7 kJ・mol–1 which was close to values (50.4, and 60.9 kJ・mol–1) already reported on copper(II) oxide. Upon comparing the rate of CuO/SiO2 reduction with that of the exchange reaction involving the redox of Cu(O)/SiO2+H2⇄Cu( )/SiO2+H2O, the rate of the exchange reaction was higher than that of the reduction of CuO/SiO2. It was deduced that oxygen of Cu(O) on the silica support behaved like oxygen on copper based catalyst used for WGS reaction, while oxygen of CuO supported on the support showed the analogous property to copper(II) oxide species. In addition, it was suggested that reduction rate of CuO on the support at low temperature range for the initiation step was hardly detected by the usual TPR method which requires high temperature raising rate.
