ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland.
ChemSusChem. 2013 May;6(5):831-9. doi: 10.1002/cssc.201200703. Epub 2013 Apr 3.
Desilication of commercial MFI-type (ZSM-5) zeolites in solutions of alkali metal hydroxides is demonstrated to generate highly selective heterogeneous catalysts for the aqueous-phase isomerization of biobased dihydroxyacetone (DHA) to lactic acid (LA). The best hierarchical ZSM-5 sample attains a LA selectivity exceeding 90 %, which is comparable to that of the state-of-the-art catalyst (i.e., the Sn-beta zeolite); this optimized hierarchical catalyst is recyclable over three runs. The Lewis acid sites, which are created through desilication along with the introduction of mesoporosity, are shown to play a crucial role in the formation of the desired product; these cannot be achieved by using other post-synthetic methods, such as steaming or impregnation of aluminum species. Desilication of other metallosilicates, such as Ga-MFI, also leads to high LA selectivity. In the presence of a soluble aluminum source, such as aluminum nitrate, alkaline-assisted alumination can introduce these unique Lewis acid centers in all-silica MFI zeolites. These findings highlight the potential of zeolites in the field of biomass-to-chemical conversion, and expand the applicability of desilication for the generation of selective catalytic centers.
商业 MFI 型（ZSM-5）沸石在碱金属氢氧化物溶液中的脱硅作用被证明可以生成用于生物基二羟丙酮（DHA）水相异构化为乳酸（LA）的高选择性多相催化剂。最佳的分级 ZSM-5 样品达到了超过 90%的 LA 选择性，与最先进的催化剂（即 Sn-beta 沸石）相当；这种优化的分级催化剂在三个运行周期内是可回收的。通过脱硅和引入介孔而产生的路易斯酸位在形成所需产物中起着关键作用；这些无法通过使用其他后合成方法（例如蒸汽处理或铝物种浸渍）来实现。其他金属硅酸盐（如 Ga-MFI）的脱硅也导致了高的 LA 选择性。在可溶性铝源（如硝酸铝）的存在下，碱性辅助的氧化铝化可以在全硅 MFI 沸石中引入这些独特的路易斯酸中心。这些发现强调了沸石在生物质转化为化学物质领域的潜力，并扩展了脱硅用于生成选择性催化中心的适用性。
