Zeolites in Microsystems for Chemical Synthesis and Energy Generation
Zeolites in Microsystems for Chemical Synthesis and Energy Generation
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DOI：
10.1007/s11244-008-9146-4
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发表时间：
2009-01
影响因子：
3.6
通讯作者：
K. Yeung;S. M. Kwan;W. N. Lau
中科院分区：
文献类型：
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作者：
K. Yeung;S. M. Kwan;W. N. Lau
沸石分子筛作为膜和催化剂应用于便携式能源生产和精细化学合成的化学微系统中。将微型HZSM-5分子筛微膜用作微型直接甲醇燃料电池（μ-DMFC）的质子交换膜。HZSM-5微膜良好的质子导电性归因于质子沿着水分子桥连邻近铝位的Grotthus扩散。6-μm厚的HZSM-5微膜表现出与Nafion®117相当的质子通量，在室温下提供2.9 mW cm−2（E= 0.33 V）的aPmax。与基于Nafion®的μ-DMFC的16.5 mW cm−2（E= 0.23 V）相比，这是较小的，并且被认为是由吸附的甲醇分子中断质子沿水桥的沿着传输引起的。在微型反应器通道中，采用铯交换的NaX/NaA双层催化膜，催化苯甲醛与氰基乙酸乙酯、乙酰乙酸乙酯和丙二酸二乙酯的Knoevenagel缩合反应。与固定床和间歇式反应器相比，微反应器和膜微反应器提供了更高的转化率，但苯甲醛和EAA在微反应器中的反应具有较差的选择性，这是由于产物分子在微通道中的缓慢扩散使得它们的进一步反应形成不期望的副产物。
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 (μ-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-μm thick HZSM-5 micromembrane exhibited comparable proton flux as Nafion®117 and delivered aPmaxof 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®-based μ-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.