Aluminum fluoride catalytic performances

Table 6.3 Catalytic performances of the different aluminum fluoride samples in the synthesis...

Therefore, noble metal (e.g., Pd, Pt, Ir)-doped hydroxylated aluminum fluorides were prepared via the fluorolytic sol-gel method and applied in the citral hydrogenation [84]. For a better understanding of the different reactions that require different active sites, the catalytic tests should be performed in two steps (1) the ( )-citronellal isomerization to isopulegols that desires only acidic sites and (2) the one-pot synthesis of menthols from citral that requires acid and hydrogenation sites. 

Therefore, two questions that arose are as follows (1) how the catalysts structure can be stabilized against the harsh reaction conditions concomitant with keeping the catalytic performances, and (2) to which extent the leached aluminum hydroxide fluoride species may influence the reaction performances ... 

On the other hand, the 25Nb AlF3 sample recovered after the separation of leached aluminum species became highly selective to hydroxy acids, with a preponderant formation of lactic acid, while the conversion of cellulose decreased only by a few percent when compared with the fresh catalyst (Table 6.9, entry 7). This catalytic performance improvement is clearly due to the leaching of aluminum that enriches the catalyst in niobium oxide fluoride phases (boiled catalyst contains 42.5 mol% Nb and 57.5 mol% A1 as against fresh catalyst (25 mol% Nb and 75 mol% Al)) alongside the introduction of an oxygen/aluminum vacancy adjacent to the niobium sites (NbOF - Lewis acid sites), by the formation of different sixfold coordinated Al units AlF Og. , fivefold coordinated units AIF 05, and fourfold coordinated species AlF 04 t- This way an optimum combination of acidity for the one-pot transformation of cellulose to lactic acid seems to be created. 

The Henry reaction is routinely performed in the presence of only catalytic quantities of a base. Several base catalysts including alkali metal hydroxides, carbonates, bicarbonates, alkoxides, calcium and barium hydroxides and magnesium and aluminum ethoxides have been used. Anion-exchange resins and, among organic bases, primary and tertiary amines and ammonium acetate and fluoride have proven to be... 

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