The initial products of the photoreduction of gaseous CO2 in Ti silicalite molecular sieve using methanol as electron donor have been monitored by in-situ FT-IR spectroscopy. Reaction was induced by 266 nm excitation of the Ti+IV−O-II → Ti+III−O-I ligand-to-metal charge-transfer transition of the framework center. HCO2H, CO, and HCO2CH3 were the observed products. CO escaped instantaneously into the gas phase and was recorded at high spectral resolution. The origin of the products was elucidated by infrared analysis of experiments with C18O2, 13CO2, and 13CH3OH. The results show that CO originates from secondary photolysis of HCO2H, while HCO2CH3 emerges mainly from spontaneous Tishchenko reaction of CH2O, the initial oxidation product of methanol. The key finding is that formic acid is the primary 2-electron reduction product of CO2 at the LMCT-excited Ti centers. This implies that C−H bond formation occurs in the initial steps of CO2 activation at the gas−micropore interface.

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Investigations of the pore expansion in mesoporous silica in the presence of n-alkanes suggest a cooperative organization of the surfactant and alkane molecules, involving additivity of chain lengths.The discovery of mesoporous silica by Beck et al. involving an unusual combination of supramolecular cationic surfactant aggregates and anionic silicate species is a fine example of cooperative organization. The formation of supramolecular aggregates here is favoured by the hydrophobic interactions between the surfactant chains. Such an organization of ionic organic and inorganic molecular species to produce periodic arrays can be understood on the basis of the model of Stucky and coworkers.2,' The pore size in mesoporous silica can be expanded by the addition of various organic molecules, in particular 1,3,5-trimethyIbenzene (TMB), the hydrophobic solvation interactions of the aromatic molecules playing the key role.1.2 We have investigated the systematics in the pore size expansion when normal alkanes, C,,H2, + 2, are employed as solubilizing agents, with the expectation that the study may throw light on the nature of the supramolecular organization of the different species involved in the process.By employing hexadecyltrimethylammonium bromide as the surfactant (SA), we have prepared mesoporous silicas starting with gels of the composition SiO2 : Na20 : SA : alkane : H20 ( 1 : 0.08 : 0. I6 : 0.16 : 63) prepared from the appropriate quantities of tetraethylorthosilicate, NaOH, SA, alkane and distilled water. The molar ratio of the surfactant and the alkane was kept at 1 : 1, since this ratio was optimal for obtaining the maximum possible pore size with a given alkane just as in the case of TMB.2 The gels were subjected to hydrothermal treatment at 01 10 ' O dl 00 / A

Mesoporous chromium-containing silicates of the MCM-41 type (pore size ca. 2.8 nm) with redox catalytic properties are synthesized and characterized.

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