Semi-heterogeneous catalysis

In general terms, the interest in metal nanoparticles as catalysts is increasing dramatically, as reflected by the large number of publications in the last five years. This field, defined as semi-heterogeneous catalysis , is recording a substantial progress in terms of efficiency and selectivity of reactions on one hand, and recovery and recyclability of the catalytic materials, on the other. As far as nanoparticles in catalysis are concerned, the reader is directed to the excellent review article by Astruc et al. 

Some of the systems where the symmetry is low and the number of atoms relatively high are those occurring in the field of heterogeneous catalysis. The combination of a surface of a (in the ideal case, semi-infinite) crystal and one or more finite molecules (maybe even together with the presence of some medium) makes the study of the chemical reactions on the surfaces of crystals very complicated. In Section 6 we saw that such studies are becoming possible but still only for the simplest reactions on fairly idealized surfaces. Moreover, the calculations explore mainly energetical aspects and not kinetic aspects of the reactions. This means also that the time scales that can be treated with quantum-mechanical molecular-dynamics simulations are much too small (10 -10 s) compared with those that often are relevant for chemical reactions. 

Keywords heterogeneous catalysis, nanocatalyst, palladium, semi-hydrogenation. 

Because of the heterogeneous nature of methloninase catalysis (Figure 1), measurement of alpha-ketobutyrlc acid (as well as other carbonyls that may be present) may not provide accurate Indications of the activity of the enzyme. Comparison of the data in Figure 2 for cell-free extracts and semi-purified freeze dried methloninase solutions suggests that either protease activity was involved or that complex Interactions of potential substrates and products occurred. Use of alpha-ketobutyrlc acid assays for methloninase activity in samples Incubated for prolonged periods seems potentially vulnerable to such analytical pitfalls. 

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