A One-Step Facile Encapsulation of Zeolite Microcrystallites in Ordered Mesoporous Microspheres
A One-Step Facile Encapsulation of Zeolite Microcrystallites in Ordered Mesoporous Microspheres
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DOI：
10.1021/acs.iecr.0c02054
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发表时间：
2020-08-05
影响因子：
4.2
通讯作者：
John, Vijay
中科院分区：
文献类型：
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作者：
Farinmade, Azeem;Ajumobi, Oluwole;John, Vijay
采用气溶胶辅助技术设计了一种新型的球形复合沸石催化剂材料。该技术能够一步将沸石微晶包封到球形介孔二氧化硅颗粒载体如MCM-41的基质中。通过将预合成的沸石微晶引入到含有模板表面活性剂和二氧化硅前体的前体溶液中，然后通过大于微晶的喷嘴雾化，可以将微晶夹带在气溶胶液滴中。液滴通过炉的加热区的运输导致每个液滴中的二氧化硅前体（原硅酸四乙酯，TEOS）的水解和冷凝，并形成含有嵌入的沸石微晶的MCM-41的球形颗粒。这种瓶绕船程序，使沸石-MCM-41复合材料是非常有效的，可以很容易地扩大规模。这些复合颗粒的详细表征表明，高达75重量%的ZSM-5沸石可以嵌入在MCM-41微球中，而不会损失颗粒形态的保真度。为了验证反应物对沸石的访问，我们在MCM-41中封装之前用镍浸渍ZSM-5（Ni@ZSM-5），并且已经显示了该系统对4-硝基苯酚液相催化还原为4-氨基苯酚的模型反应的可行性。虽然反应有效地进行，但对4-硝基苯酚的传输存在扩散限制，导致复合催化剂有效因子为0.4。将沸石晶体封装在微米尺寸的中孔MCM-41壳内为沸石提供了结构稳定性，并且由于复合物的粒度增加，可以降低固定床管式反应器的压降。这种复合颗粒的潜在应用包括MCM-41作为焦炭和催化剂毒物的牺牲吸附剂的能力，从而延长活性材料的寿命。
A facile aerosol-assisted technique was employed for the design of a new class of composite zeolite catalyst material with spherical morphology. This technique enables the one-step encapsulation of zeolite microcrystals into the matrix of spherical mesoporous silica particle supports such as MCM-41. By introducing presynthesized zeolite microcrystals into precursor solutions containing the templating surfactant and the silica precursor followed by aerosolization through nozzles larger than the microcrystals, it is possible to entrain the microcrystals in the aerosol droplet. Transport of the droplet through the heated zone of the furnace leads to hydrolysis and condensation of the silica precursor (tetraethyl orthosilicate, TEOS) in each droplet and the formation of spherical particles of MCM-41 containing embedded zeolite microcrystals. This bottle-around-a-ship procedure to make zeolite-MCM-41 composites is extremely effective and can be easily scaled up. Detailed characterization of these composite particles reveals that up to 75 wt % of ZSM-5 zeolite can be embedded in MCM-41 microspheres with no loss of fidelity in particle morphology. To verify access of the reactants to the zeolite, we impregnated the ZSM-5 with nickel (Ni@ZSM-5) prior to encapsulation in MCM-41, and have shown the feasibility of the system to the model reaction of the liquid phase catalytic reduction of 4-nitrophenol to 4-aminophenol. While the reaction proceeds efficiently, there are diffusional restrictions to the transport of 4-nitrophenol resulting in a composite catalyst effectiveness factor of 0.4. The encapsulation of zeolite crystals within a micrometer-sized mesoporous MCM-41 shell provides structural stability to the zeolites and could reduce the pressure drop across a fixed bed tubular reactor due to the increased particle size of the composite. Potential applications of such composite particles include the ability of the MCM-41 to act as sacrificial adsorbents for coke and catalyst poisons, thus extending the life of the active material.