Zeolites in Microsystems for Chemical Synthesis and Energy Generation

Zeolites were incorporated as membrane and catalyst in chemical microsystems for portable energy generation and fine chemical synthesis. Microfabricated HZSM-5 micromembrane was used as a proton-exchange membrane in a miniature direct methanol fuel cell (mu-DMFC). The good proton conductivity of HZSM-5 micromembrane was attributed to a Grotthus-like diffusion of protons along the water molecules bridging neighboring aluminum sites in the hydrated HZSM-5. The 6-mu m thick HZSM-5 micromembrane exhibited comparable proton flux as Nafion(A (R)) 117 and delivered a P (max) of 2.9 mW cm(-2) (E = 0.33 V) at room temperature. This is smaller compared to 16.5 mW cm(-2) (E = 0.23 V) for a Nafion(A (R))-based mu-DMFC and was believed to be caused by adsorbed methanol molecules interrupting the proton transport along the water bridge. A Cs-exchanged NaX on NaA bilayer catalyst-membrane incorporated in microreactor channels was used for the Knoevenagel condensation reactions between benzaldehyde and (1) ethyl cyanoacetate, (2) ethyl acetoacetate (EAA) and (3) diethyl malonate. Microreactor and membrane microreactor gave higher conversion compared to fixed-bed and batch reactors, but the reaction of benzaldehyde and EAA in the microreactor had poorer selectivity due to the slow diffusion of the product molecules in the microchannel that allowed their further reactions to form undesired byproducts.