Search

Raman microscopy is applied to monitor the preparation of shaped Mo/Al2O3 catalysts. It is illustrated that the time-resolved in situ Raman microscopy can be used to study the physicochemical processes during the preparation of supported catalysts.

The time resolved UV-Vis and IR spectroscopies of Re(bz)(CO)3(iPr-DAB), where Bz is benzyl and iPr-DAB is N,N'-diisopropyl-1,4-diazabutadiene, detect the reactive sigma-pi* excited state. During the photochemical homolysis of the Re-Bz bond, this excited state acts as an intermediate. The complex after excitation to its MLCT visible absorption band suffers homolysis. The spin-triplet nature of the sigma-pi* excited state and small excited state distortion makes it highly stable.

Raman microscopy has been applied to study the preparation of shaped Mo/Al2O3 catalysts. The speciation of different Mo complexes over γ-Al2O3 support bodies was followed in time after pore volume impregnation with aqueous solutions containing different Mo complexes. The addition of NO3 to the impregnation solutions allows for a quantitative Raman analysis of the distribution of different complexes over the catalyst bodies as this ion can be used as an internal standard. After impregnation with an acidic ammonium heptamolybdate (AHM) solution, the strong interaction between Mo7O246- and Al2O3 results in slow transport of this complex through the support and extensive formation of Al(OH)6Mo6O183- near the outer surface of the support bodies. This may be prevented by decreasing the interaction between Mo and Al2O3. In this way, transport is facilitated and a homogeneous distribution of Mo is obtained on a reasonable time scale. A decrease in interaction between Mo and Al2O3 can be achieved by using alkaline impregnation solutions or by the addition of complexing agents, such as citrate and phosphate, to the impregnation solution. In general, time-resolved in situ Raman microscopy can be a valuable tool to study the physicochemical processes during the preparation of supported catalysts. [ABSTRACT FROM AUTHOR]