An In-Situ Atomic Force Microscopy Study of the Dissolution of Nanoporous SAPO-34 and SAPO-18

In-situ atomic force microscopy has been used to investigate the dissolution behavior of industrially relevant silicoaluminophosphate catalysts SAPO-34 and SAPO-18. Spiral growth is prevalent on these materials and it is common for the spirals to be composites of multiple dislocation sources. The spirals dissolve via classical step retreat and the structure dissolves in a two-step process via unstable intermediates. The data support the proposition that the terminating surface of SAPO-34 is composed of double 6-rings. SAPO-34 and SAPO-18 both dissolve by removal of the same structural units with similar mechanisms

High Pressure Adsorption of CO₂ and CH₄ on Zr-MOFs

Adsorption equilibrium of CO₂ and CH₄ at three different temperatures was measured on three isoreticular Zr-MOFs: Zr­(1,4-BDC) (UiO-66), Zr­(4,4′-BPDC) UiO-67, and Zr­(2,6-NDC) (DUT-52). Adsorption equilibrium data was measured at 298, 313, and 343 K up to 30 bar for CO₂ and 80 bar for CH₄. The three adsorbents have increasing surface areas, pore volumes, and pore sizes in the order UiO-66 < DUT-52 < UiO-67. The maximum CO₂ and CH₄ loading and selectivity follow the same trend. The relatively low isosteric heats of adsorption of CO₂ for the three adsorbents indicate potential application at high partial pressures of CO₂ in so-called precombustion schemes. Since equilibrium selectivity was higher for UiO-67, adsorption kinetics of pure gases was also measured in this adsorbent. Diffusion of both molecules is very fast, allowing the use of equilibrium theory for estimation of process performance of this adsorbent

MCM-41, MOF and UiO-67/MCM-41 adsorbents for pre-combustion CO2 capture by PSA: Adsorption equilibria

ISSN:0929-5607ISSN:1572-875

Nanoporous Intergrowths: How Crystal Growth Dictates Phase Composition and Hierarchical Structure in the CHA/AEI System

Some of the most important nanoporous materials that are used for industrial applications are formed as intergrowths between structurally related phases. Further, the specific properties and functions are often strongly related to the nature of these intergrowths. By their nature such structures are notoriously difficult to characterize in detail and thereby formulate a structure/property relationship. We approach the problem of the industrially relevant CHA/AEI intergrowth system by getting insight into not only the structure of the materials but also the crystal-growth mechanism and show that the former is crucially dependent upon the latter. Through a detailed X-ray diffraction analysis with optimization of the CHA/AEI layer stacking sequence, it is shown that up to three distinct components are present. These consist of the two end member structures intimately cocrystallizing with an intergrowth structure. The intergrowth composition is further corroborated by nuclear magnetic resonance and unit cell measurements. The mechanism by which these complex intergrowth structures form is revealed by atomic force microscopy that shows there are at least two competing mechanisms of growth at the surface: layer-by-layer and spiral. This has profound consequences on the resulting intergrowth materials, as intergrowth formation is not permitted in spiral growth. The competition from the lower energy spiral growth at screw dislocations does not allow intergrowth formation and consequently results in blocks of pure-phase AEI or CHA. Owing to this competitive growth nature, the different possibilities furnish the material with its higher level hierarchical structure

Nanoporous Intergrowths: How Crystal Growth Dictates Phase Composition and Hierarchical Structure in the CHA/AEI System

Some of the most important nanoporous materials that are used for industrial applications are formed as intergrowths between structurally related phases. Further, the specific properties and functions are often strongly related to the nature of these intergrowths. By their nature such structures are notoriously difficult to characterize in detail and thereby formulate a structure/property relationship. We approach the problem of the industrially relevant CHA/AEI intergrowth system by getting insight into not only the structure of the materials but also the crystal-growth mechanism and show that the former is crucially dependent upon the latter. Through a detailed X-ray diffraction analysis with optimization of the CHA/AEI layer stacking sequence, it is shown that up to three distinct components are present. These consist of the two end member structures intimately cocrystallizing with an intergrowth structure. The intergrowth composition is further corroborated by nuclear magnetic resonance and unit cell measurements. The mechanism by which these complex intergrowth structures form is revealed by atomic force microscopy that shows there are at least two competing mechanisms of growth at the surface: layer-by-layer and spiral. This has profound consequences on the resulting intergrowth materials, as intergrowth formation is not permitted in spiral growth. The competition from the lower energy spiral growth at screw dislocations does not allow intergrowth formation and consequently results in blocks of pure-phase AEI or CHA. Owing to this competitive growth nature, the different possibilities furnish the material with its higher level hierarchical structure

Fundamental aspects of H \u3c inf\u3e 2 S adsorption on CPO-27-Ni

Adsorption of H2S on the Ni2(dhtp)(H 2O)2·8H2O metal-organic framework (known as CPO-27-Ni or MOF-74-Ni) is characterized by in situ powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), Raman, and UV-visible spectroscopy) and by first-principles periodic boundary conditions calculations. PXRD results show very high stability of CPO-27-Ni framework in the presence of H 2S. Nevertheless, as evidenced by change in color of the sample from pale yellow to dark green, the adsorption of H2S strongly affects the coordination of Ni sites. FTIR results show the reversible molecular adsorption of H2S. Experimental and computed energies of interaction reveal good agreement. Quantitative data considering energetic aspects (calorimetric measurements) are also included. This work highlights the fundamentals of H 2S adsorption onto the CPO-27-Ni framework. © 2013 American Chemical Society