The Differences in Surface and Catalytic Properties of Two Magnesium Oxides Prepared from the Hydroxide and the Carbonate Hydroxide

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Abstract
Two kinds of MgO were prepared; MgO(I) from magnesium hydroxide and MgO(II) from magnesium carbonate hydroxide by evacuating at various temperatures and their surface and structural properties and catalytic actions for alkylation and isomerization reactions were examined. IR spectra of CO2 retaining or adsorbed showed broad bands on MgO(II), but relatively sharp bands on MgO(I). In the alkylation of phenol with methanol over MgO(I), phenol was selectively alkylated at the ortho positions to produce o-cresol and 2,6-xylenol. The ortho-selectivity of MgO(I) was higher than 96%, while that of MgO(II) was about 75%. A low selectivity of MgO(II) was considered to be caused by a heterogeneity of surface structure of MgO(II), which was suggested by broad IR bands of CO2 species on MgO(II). For the isomerization of 1-butene, both of MgO became active when evacuated at 450 °C and showed maximum activities when evacuated at 600 °C. The activity and the selectivity (ratio of cis-2-butene to trans-2-butene) of both catalysts were not much different. However, for the isomerization of cis-2-butene, the maximum activity and the selectivity (ratio of trans-2-butene to 1-butene) of MgO (I) were about four times higher than those of MgO(II).

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