Catalysis in Application
While combining a unique mix of chemistry and chemical engineering, this up-to-date text provides a snapshot of hydrogenation, dehydrogenation, chiral catalysis, environmental catalysis, and catalyst deactivation.
TABLE OF CONTENTS Catalysis in Application
3: CORRELATION OF SOLID-STATE REACTIVITY AND CATALYTIC PERFORMANCE
3 CORRELATION OF SOLID-STATE REACTIVITY AND CATALYTIC PERFORMANCE
The statement about a connection between bulk reactivity and catalytic performance needs confirmation by an in-situ experiment. Pure MoO 3 was used as a model substance for selective oxidation of C3 compounds approximated by propene oxidation to acrolein. Well-ordered single crystalline MoO 3 is inactive in this reaction9. Defective varieties were prepared by in-situ decomposition of ammonium heptamolybdate (AHM) or H 3[PMo 12O 40] (HPA).
The bulk reactivity of these oxides was determined by in-situ observation of the re-oxidation of MoO 2 to MoO 3. The reverse of the expected partial reduction was chosen as the dioxide is structurally well defined and allows a quantitative determination of the fractional degree of conversion ( ?). The data were obtained by time-resolved NEXAFS at the Mo K-edge10. The raw data were subject to principal component analysis and correlated with the spectral weights of MoO 2 and MoO 3 respectively. No stable intermediates occur under these conditions. Figure 3 shows results for a series of isothermal experiments. The phase change between MoO 2 and MoO 3 occurs instantaneously with the changing chemical potential of oxygen as seen by comparing the gas pulse profile with the normalised conversion curves. Their shape at various temperatures is qualitatively different exhibiting a diffusion-controlled kinetics for low temperatures and a nucleation-controlled kinetics at higher temperatures. The inset in Figure 3 shows the curves on a...
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