Efficient aerobic oxidation of alcohols catalyzed by NiGa hydrotalcites in the absence of any additives

Abstract

The surface Brønsted OH basic site on NiGa hydrotalcites was suggested to be the key active site for the oxidation.

Efficient Synthesis of α,β‐Unsaturated Ketones from Primary Alcohols and Ketones over Mg2+‐Modified NiGa Hydrotalcites

“…On the basis of the above analysis, a series of Ni 2 Mg x Ga‐LDH (x=1, 1.5 and 2) were synthesized through copreciptation method. Moreover, Ni 3 Ga‐LDH was also prepared for comparision, which exhibited the highest activity among the hydrotalcites with various Ni/Ga ratios in the aerobic oxidation of benzyl alcohol . The powder XRD patterns for all the samples showed in Figure evidently exhibit similar reflections.…”

“…However, the ratio of the three metals were similar, suggesting that the distribution was homogeneous on the surface. The SEM image (Figure ) shows that layered hydrotalcite structure was formed for the prepared NiMgGa samples, but the plate‐like shape was not quite distinguishable as that of some other hydotalcites ,. The aggregation of the disordered lamellate sheets and formation of large assembles are observed, which might be related to the composition and the preparation method.…”

“…Two split broad bands of maxima at 756, 660 and 422, 381 nm, respectively, could be observed for all the Ni 2 Mg x Ga and Ni 3 Ga hydrotalcites (Figure ). The results are accordance to that of NiMgAl hydrotalcites,, suggesting that Ni(II) is octahedrally coordinated in all the prepared samples.…”

“…The cations and anions in the brucite layer and interlayer significantly influence the surface properties of LDHs, and introduction of Mg 2+ has been proved to be effective to improve the surface basicity in our previous study . Although calcination can also improve the strength of surface basicity, it will decrease the catalytic activity in the alcohol oxidation ,. Therefore, a series of Mg 2+ modified NiGa LDHs were prepared in the present study, and investigated in the aerobic oxidation of alcohol/ aldol condensation between aromatic alcohols and ketones.…”

“…On the basis of above analysis, it is still highly desirable to develop efficient bifunctional catalyst originated from non‐noble metals for the tandem reaction to synthesize α, β ‐unsaturated ketones. During our research of developing heterogeneous catalyst for selective oxidation, NiGa hydrotalcite have been found efficient for the alcohol oxidation using molecular oxygen as the oxidant . The results also indicated that the active sites are the structural nikel and the Brønsted OH basic site.…”