【摘要】 研究了共沉淀法制备Mo-Bi-Fe-Co-Mn五组分催化剂过程中溶液的pH值对催化剂中物种存在状态的影响.并考察其异丁烯选择氧化制备甲基丙烯醛(MAL)的反应性能.结合粉末X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)、氮气吸附-脱附和H2程序升温还原(H2-TPR)等表征手段对催化剂的结构进行了详细的研究.结果表明,溶液的pH值对催化剂结构和组成有明显的影响.催化剂中某种特定物相MX随沉淀的pH值的提高而增加,当pH=7时,催化剂中MX相的量达最大值.此时,异丁烯的转化率和甲基丙烯醛的选择性分别为99.9%和95.6%.进一步提高沉淀的pH值,催化剂中MX相的量减少,异丁烯的转化率和甲基丙烯醛的选择性也相应降低.研究表明,催化剂上各组分间存在一定的相互作用,催化剂中的特定物相MX是影响反应活性的关键因素之一.更多还原

【Abstract】 The effect of different pH values on Mo-Bi-Fe-Co-Mn multiphasic oxide catalysts prepared via co-precipitation methods was studied.In addition,selective oxidation of isobutylene to methacrolein(MAL) reaction was evaluated.The structures and crystal phases of the catalysts were characterized by X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,X-ray photoelectron spectroscopy(XPS),N2 adsorption-desorption,and temperature-programmed reduction of H2(H2-TPR).The characterization results showed that the structures and properties depended on the pH during preparation.The amount of the special crystalline phase MX on the catalysts increased with increasing pH value during the preparation process.When the precipitation pH value was 7,the crystalline phase MX reached maximum levels on the corresponding sample.The conversion of isobutene and selectivity for methacrolein were 99.9% and 95.6%,respectively.When increasing the precipitation pH,the MX content decreased,and the conversion of isobutene and selectivity for methacrolein decreased.The results revealed that synergistic effects or cooperation between multiphasic oxides and the special phase MX might be important for improving catalytic performance.更多还原