Functioning catalysts investigations

In this study we have investigated utilizing a bi-functional catalyst with a solid base function for the aldol condensation reaction and a metal function for the hydrogenation. This work is a continuation of the study that examined the supported base catalyzed aldol condensation of acetone (5, 6). In those studies... 

In the future, we can expect the development of novel experimental techniques in solid-state NMR spectroscopy for investigation of functioning catalysts. Important goals are (i) the enhancement of the sensitivity of solid-state NMR spectroscopy, for example, by a selective enhancement of the nuclear polarization taking advantage of laser-polarized xenon, (ii) increases in the temperature range accessible for the characterization of solid-catalyzed reactions, and (iii) the coupling of NMR spectroscopy with other techniques such as mass spectrometry. Furthermore, modern two-dimensional techniques of solid-state NMR spectroscopy such as MQMAS NMR spectroscopy will be applied to improve the resolution of the spectra. 

It is often fruitful to characterize functioning catalysts with more than one technique. ATR-IR and UV-vis spectroscopies were used in combination to investigate alcohol oxidation on a Pd/AFOj catalyst 96). The two methods provide complementary information ATR spectroscopy was used to identify dissolved reaction products and species adsorbed on the catalyst and support, and UV-vis spectroscopy is sensitive to changes of the catalyst itself. 

Recently, highly dispersed, highly active, or highly functional catalysts have been extensively investigated to reduce the amount of catalyst required for recovery and regeneration (61-68). 

This appears to be the first report of the addition of H2 to the silylformyla-tion reaction mixture. Good yields are obtained when Et3SiH or PhjSiH is used in the reaction of 1-hexyne or 4-phenyl-l-butyne. Although a variety of functionally substitued terminal alkynes have been studied, most lead only to the silylformylation product and do not appear to be affected by the presence of H2 in the system. Other rhodium catalysts investigated, such as [Rh(COD)(dppb)]+BPh4 and Rh6(CO)16, catalyze the silylformylation reaction even under H2 pressure and do not lead to any of the silylhydrofor-mylated products. 

It is usually considered sufficient to report the structural modifications before and after reaction experiments. The ample evidence of the differences provides an overwhelming justification for applying XRD to functioning catalysts and not relying simply on XRD of the fresh catalyst, as has been done in the vast majority of catalytic investigations with XRD. 

This final section includes a brief outline of suggested future research directions, aimed at applying spectroscopy of functioning catalysts to more complex catalysts and reactions, mimicking technological systems even more closely. It is emphasized that such model investigations will have to sacrifice part of the control of surface structure and composition and cope with problems similar to those occurring on real catalysts. 

Investigations of functioning catalysts with Mossbauer spectroscopy have been performed for a wide range of samples and applications. The reactions include hydrodesulfuration 15), the Fischer-Tropsch reaction (20,180), selective oxidation or oxidative dehydrogenation (181-186), and acetonitrile synthesis (187). 

In Figure 3 the total yield of syncrude and gas produced by cracking on the different catalysts investigated is plotted as a function of the conversion. If a comparison is made between the MCM-41, Si-VPI-5 and the equilibrium catalyst at the same conversion level (e g, 50 %) it can be concluded that these materials produce higher gas yields and lower syncrude yields compared with the equilibrium catalyst. This indicates even "deeper" cracking of MCM-41 and Si-VPI-5. 

Characterization has been done most successfully by Infrared spectroscopy and EXAFS, and both these techniques can be combined with measurements of catalytic kinetics to allow Investigation of functioning catalysts. 

Abascal NC, Lichtor PA, GiuUano MW, Miller SJ (2014) Function-oriented investigations of a peptide-based catalyst that mediates enantioselective allylic alcohol epoxidation. Chem Sci 5 4504- 511... 

Rode et al. [64] investigated propylene hydroformylation by such a catalyst and measured the infrared spectra of the functioning catalyst. They conduded that the rhodium carbonyl duster was not the catalytically active spedes, but, instead, a mononuclear rhodium spedes was suggested to be the active spedes. 

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