Kinetic studies on the water-gas shift reaction catalyzed by magnetite/chromium oxide and copper/zinc oxide were carried out by using an in situ photoacoustic spectroscopic technique. The reactions were performed in a closed-circulation reactor system using a differential photoacoustic cell at total pressure of 40 Torr in the temperature range of 100 to 350 o C. The CO 2 photoacoustic signal varying with the concentration of CO 2 during the catalytic reaction was recorded as a function of time. The time-resolved photoacoustic spectra obtained for the initial reaction stage provided precise data of CO 2 formation rate. The apparent activation energies determined from the initial rates were 74.7 kJ/mol for the magnetite/chromium oxide catalyst and 50.9 kJ/mol for the copper/zinc oxide catalyst. To determine the reaction orders, partial pressures of CO(g) and H 2 O(g) in the reaction mixture were varied at a constant total pressure of 40 Torr with N 2 buffer gas. For the magnetite/chromium oxide catalyst, the reaction orders with respect to CO and H 2 O were determined to be 0.93 and 0.18, respectively. For the copper/zinc oxide catalyst, the reaction orders with respect to CO and H 2 O were determined to be 0.79 and 0, respectively.

The wavelength dependence of the photoacoustic signal for n-type GaAs semiconductors in the region of the band-gap energies was investigated. The significant changes in the phase and amplitude of the photoacoustic signal near the band-gap absorption wavelengths were observed to occur when the Si-doping densities in GaAs were varied. Particularly, the first derivatives of the photoacoustic phase vs. wavelength graphs were evaluated and fitted with single Gaussian functions. The peak centers and the widths of the Gaussian curves clearly showed linear relationships with the log values of the Si-doping densities in n-type GaAs semiconductors. It is proposed that the wavelength-dependent PA spectroscopy can be used as a simple and nondestructive method for measuring the doping densities in bulk semiconductors.