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 Computational Investigation of IPC-1P and MWW Layered Zeolite Frameworks
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Tác giả hoặc Nhóm tác giả: Lukas Grajciar, Ho Viet Thang, Petr Nachtigall
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Nơi đăng: Workshop on Layered Materials. Challenges in layered materials: Synthesis, Characterization, Properties. September 11-14, 2013. Liblice Castle, Czech Republic; Số: 2013;Từ->đến trang: O4;Năm: 2013
Lĩnh vực: Khoa học; Loại: Báo cáo; Thể loại: Quốc tế
TÓM TẮT
Layered zeolite frameworks (LZF) represent an intriguing field of study as the so-called 2-D zeolites constitute an important intermediate step in searching for novel synthesis routes for obtaining either the known or even new 3-D zeolites in certain types of adsorption and catalysis, e.g. the elimination of the diffusion elimination of the diffusion limitations for bulky adsorbates.The goal of the present study was to computationally investigate the properties of the two representative LZF, namely the frameworks formed by IPC-1 and MWW layered that could be inferred from UTL and MCM-22 zeolites, respectively. The aims of the investigation were twofold: i) test the reliability of the computational methods for description of inter-layer interactions in LZF (the IPC-1 study), and ii) determine the role of inter-layer hydrogen bonds between surface silanols on the overall inter-layer stabilization and arrangement (the presence of the water or structure directing agent (SDA) in the inter-layer region was not considered).First, it was shown that standard dispersion-corrected density functionals perform rather well for inter-layer interaction (being in error of 10-20% with respect to the reference high-level calculation for cluster models of layers) with non-local exchange-correlation functional vdW-DF2 providing the best accuracy. Using then the vdW-DF2 functional it was observed that the mode of the layer interaction ( the role of inter-layer hydrogen bonds on overall stabilization) is largely dependent on the density of surface silanols. In case of IPC-1 with high surface silanol density (43A2 per silanol) the interaction between the layers is dominated by the inter-layer silanol hydrogen bonds accounting for about 80% of overall interaction. Interestingly, the most stable mutual arrangement of layers found for IPC-1 corresponds nicely to arrangement of layers found upon topotactic condensation of IPC-1 and leading to the new zeolitic framework PCR, although the role of SDA was also of a great importance in that case. In case of the MWW layers with much lower density of surface silanols (90 A2 per silanol) various structures with different inter-layer distance were found. Available experimental data are discussed in the light of calculated structures.
ABSTRACT
Layered zeolite frameworks (LZF) represent an intriguing field of study as the so-called 2-D zeolites constitute an important intermediate step in searching for novel synthesis routes for obtaining either the known or even new 3-D zeolites in certain types of adsorption and catalysis, e.g. the elimination of the diffusion elimination of the diffusion limitations for bulky adsorbates.The goal of the present study was to computationally investigate the properties of the two representative LZF, namely the frameworks formed by IPC-1 and MWW layered that could be inferred from UTL and MCM-22 zeolites, respectively. The aims of the investigation were twofold: i) test the reliability of the computational methods for description of inter-layer interactions in LZF (the IPC-1 study), and ii) determine the role of inter-layer hydrogen bonds between surface silanols on the overall inter-layer stabilization and arrangement (the presence of the water or structure directing agent (SDA) in the inter-layer region was not considered).First, it was shown that standard dispersion-corrected density functionals perform rather well for inter-layer interaction (being in error of 10-20% with respect to the reference high-level calculation for cluster models of layers) with non-local exchange-correlation functional vdW-DF2 providing the best accuracy. Using then the vdW-DF2 functional it was observed that the mode of the layer interaction ( the role of inter-layer hydrogen bonds on overall stabilization) is largely dependent on the density of surface silanols. In case of IPC-1 with high surface silanol density (43A2 per silanol) the interaction between the layers is dominated by the inter-layer silanol hydrogen bonds accounting for about 80% of overall interaction. Interestingly, the most stable mutual arrangement of layers found for IPC-1 corresponds nicely to arrangement of layers found upon topotactic condensation of IPC-1 and leading to the new zeolitic framework PCR, although the role of SDA was also of a great importance in that case. In case of the MWW layers with much lower density of surface silanols (90 A2 per silanol) various structures with different inter-layer distance were found. Available experimental data are discussed in the light of calculated structures.
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