Selective conversion of cis-2-butene-1,4-diol to 2-hydroxytetrahydrofuran over K, Ca and Ba metals-promoted Ru/SiO2 catalysts: Role of the promoter

The effect of K, Ca and Ba metals addition on the catalytic properties of SiO2 supported ruthenium catalysts in the selective liquid phase conversion of cis-2-butene-1,4-diol affording, when hydrogenated, 2-hydroxytetrahydrofuran has been investigated. Catalysts containing 5 wt% Ru and promoted with a different amount of selected first and second groupmetals salts have been prepared and characterized by TPR, XRD, TEM, FT-IR of adsorbed pyridine and CO. It has been found that promoters modify the microstructural and electronic properties of Ru particles compared with those of the undoped Ru/SiO2 sample, depending on the metal nature and loading. Consequently, the catalytic activity and selectivity towards reaction products, in cis-2-butene-1,4-diol hydrogenation, is strongly affected by the presence of promoters. In particular, K-promoted systems give an excellent selectivity to 2-hydroxytetrahydrofuran but a poor activity; whereas group IIA metals salts addition leads to an enhancement of activity and a slight increase of selectivity to the desired product with respect to the bare Ru sample. The promoted Ru catalysts behaviour is discussed in terms of charge/ionic radius ratio effect of doping cations. Finally, the salient result is the maximum yield to 2-hydroxytetrahydrofuran of 80%, so far obtained, over the sample promoted with the highest potassium loading and mainly attributed to kinetic factors.