双金属改性MCM-41催化甲醛与异丁烯Prins缩合反应

Preparation of 3-Methyl-3-buten-1-ol from Formaldehyde and Isobutene via Prins Condensation on Bimetal Modified MCM-41

通过研磨法制备了一系列不同金属负载的MCM-41催化剂,考察了单一金属及双金属负载催化剂对甲醛与异丁烯Prins缩合制备3-甲基-3-丁烯-1-醇(MBO)反应性能的影响,筛选出最佳的双金属Cu-Al负载催化剂.利用XRD、 NH3-TPD、 N2吸附、 UV-vis等表征手段对双金属改性前后催化剂的结构和酸性进行了深入分析,探究了其物质的量比例和协同作用对Prins反应性能的影响.结果表明,在温度200℃, n(异丁烯)/n(甲醛)=7,反应4 h的适宜条件下, Cu-Al(1∶1)/MCM-41对甲醛的转化率为100%, MBO产率高达98%,高于单一金属负载的催化剂. NH3-TPD表征发现Cu-Al双金属负载催化剂具有适当的酸量和适宜的酸强度,可以提高MBO的产率.Cu-Al(1∶1)/MCM-41催化剂具有一定的再生性能,连续3次再生后催化剂的比表面积和孔容明显降低,催化剂活性中心聚集导致酸量尤其是中强酸和强酸量减少是反应活性下降的主要原因.

3-Methtyl-3-buten-1-ol(MBO) is an important chemical intermediate and is widely used for producing fine chemicals. MBO is synthesized normally by Prins condensation reaction of formaldehyde and isobutene, which can utilize the excessive isobutene efficiently in petrochemical industry. The solid acidic catalyst is considered to be effective for this reaction, of which Lewis acidic catalyst may be more suitable due to the moderate acid strength. In this study, MCM-41 catalysts loaded with different metals were obtained by mechanical mixing method, and their catalytic performances in Prins condensation between formaldehyde and isobutylene were evaluated. Among them the best single metal Cu and Al modification were chosen to prepare the bimetal supported catalyst. The structure and acidity of bimetallic Cu-Al/MCM-41 were systematically characterized by means of XRD, NH3-TPD, N2 adsorption and UV-vis spectra. In addition, the Cu/Al molar ratio and the synergistic effect between them were investigated. It is found that the conversion of formaldehyde increases to 100% and MBO yield is up to 98% on Cu-Al(1∶1)/MCM-41 catalyst, which is higher than the single metal supported catalyst under the optimized reaction temperature of 200 ℃, isobutene/formaldehyde molar ratio of 7 and 4 h of reaction. The acidity characterization by NH3-TPD shows that Cu-Al(1∶1)/MCM-41 with an appropriate amount of acid sites and a proper acid strength increases the yield of MBO. Moreover, this catalyst has regeneration capability to a certain extent. After three successive regeneration cycles, its BET surface area and pore volume decrease obviously. The aggregation of the active sites may lead to the decrease in the amount of acid sites, especially the middle-strong and strong acid sites, which is the main reason for the catalyst deactivation in Prins reaction.