AlF_3催化剂的酸性表征

CHARACTERIZATION OF THE ACIDITY OF AlF 3 CATALYST

用干法制备高比表面ＡｌＦ３（Ｓ≥４５ｍ２／ｇ），对其表面酸性及酸中心类型进行了表征，并与其相结构进行了关联．对于由γ相及非晶相（二者总含量大于９５％）组成的ＡｌＦ３体系，ＮＨ３－ＴＰＤ曲线出现两个脱附峰，随着γ相含量的增加，弱酸强度变弱，强酸强度变强．脱附尾气滴定结果表明：随着γ相含量的升高，弱酸量和总酸量增加，强酸量则无显著变化，因而认为弱酸中心可能存在于ＡｌＦ３的γ相表面，强酸中心存在于其非晶相表面．吡啶吸附的红外光声光谱表明：ＡｌＦ３中既存在Ｌ酸中心，也存在Ｂ酸中心．氨气吸附的红外光谱结果表明：随着γ相含量的增加，Ｂ酸中心数量趋于减少．

The AlF 3 samples with higher surface area ( S ≥45 m 2/g) are prepared by dry method. The active sites are characterized by NH 3 TPD, NH 3 IR and FTIR photoacoustic spectra of pyridine chemisorbed (Py PAS), and correlated with their crystal content. For the AlF 3 comprising γ phase and amorphous (both total content not less than 95%), two peaks of NH 3 TPD profiles are observed. As the content of γ phase is increasing, the strength of the weaker acid sites tends to weaker and that of the stronger acid sites tends to stronger. Results of titrimetry of desorbed NH 3 with standard HCl solution indicate that the quantity of the weaker acid sites and the total acid sites increases and that of the stronger acid sites has no significant change as the content of γ phase increases. The weaker acid sites are present on the surface of γ phase, whereas the stronger are present on the surface of amorphous AlF 3. Py PAS spectra exhibit that both L and B acid sites exist on the surface of AlF 3. Results of FTIR spectra of NH 3 chemisorbed show that the quantity of B acid sites decreases with the increase of the content of γ phase.