H(Mg,Co)AlPO_4-5杂原子分子筛的酸性质测定

Determination of the Acidity of H(Mg)AlPO4-5 and H(Co)AlPO_4-5 Molecular Sieves

以红外光谱和程序升温脱附法研究了H(Mg,Co)AlPO_4-5分子筛的酸性,样品红外谱图中的3820和3680cm^(-1)谱峰分别归属于v_(Al—OH)和v_(p—OH),而3660～3568cm^(-1)谱峰则分别归属于HMgAlPO_4-5和HCoAlPO_4-5分子筛的M(OH)P(M=Mg,Co)基团的振动,酸强度顺序为:Co(OH)P>Mg(OH)P>P(OH)>Al(OH),吡啶吸附的红外光谱揭示,H(Mg,Co)AlPO_4-5分子筛具有较高酸强度的B酸和L酸中心。NH_3-TPD表明分子筛的酸强度顺序为H(Co)AlPO_4-5>H(Mg)AlPO_4-5>>AlPO_4-5。

The acidic sites of aluminophosphate molecular sieves, AlPO4-5, containing various heteroatoms such as Mg2+ and Co2+ were investigated by using IR spectroscopy of adsorbed pyridine and temperature-programmed desorption(TPD) of NH3. The band at 3680 cm-1 is assigned to P-OH, and the band at 3820 cm-1 can be attributed to the terminal Al-OH. The bands appearing in the region from 3660 to 3568 cm-1 is possibly assigned to the bridging hy-droxyl groups M (OH) P (M = Mg,Co). The decreasing acidity sequence of acidic sites is: Co(OH)P>Mg(OH)P>P(OH)>Al(OH). The IR spectra of pyridine adsorbing these samples reveal that there are strong B and L acidic sites in H(Mg)AlPO4-5 and H(Co)AlPO4-5, in contrast to AlPO4-5. Additionally, the TPD-NH3 experiments show the order of the acidic strength of these samples: H(Co)AlPO4-5>H(Mg)AlPO4-5>>AlPO4-5.