Cation Ordering and Exsolution in Copper-Containing Forms of the Flexible Zeolite Rho (Cu,M-Rho; M=H, Na) and Their Consequences for CO₂ Adsorption

Funding: UK Engineering and Physical Sciences Research Council. Grant Numbers: EP/N024613/1, EP/N032942/1, EP/L017008/1.The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals that Cu2+ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO2 rapidly at room temperature. Breakthrough tests with 10 % CO2/40 % CH4 mixtures show that Cu4.9-Rho is able to produce pure methane, albeit with a relatively low capacity at this pCO2 due to the weak interaction of CO2 with Cu cations. This is in strong contrast to Na-Rho, where cations in narrow elliptical window sites enable CO2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO2/CH4 breakthrough tests, producing pure CH4 with improved uptake and CO2/CH4 selectivity compared to that of Cu4.9-Rho.Publisher PDFPeer reviewe

Companionship of Children and Animals

This is a book review of Animality and Children’s Literature and Film. The book was written by Amy Ratelle. The author deals with (transcending) boundaries between the human and non-human in a number of classical animal stories and films for children

Kinetic Monte Carlo Simulation of the Synthesis of Periodic Mesoporous Silicas SBA-2 and STAC-1: Generation of Realistic Atomistic Models

SBA-2 and STAC-1 are two related periodic mesoporous silicas (PMSs) that have regular networks of spherical, interconnected pores; the pores are similar in the two materials but the networks differ in their symmetry. The nature of the interconnected network of pores in these materials gives rise to interesting properties related to their potential use in separation processes. In this work, we extend a kinetic Monte Carlo (kMC) technique, originally derived for MCM-41, a simpler PMS, and apply it to mimic the condensation, aggregation, deformation, and calcination stages of the synthesis of SBA-2 and STAC-1. Our simulated synthesis results suggest that the pores are connected through windows formed during micelle aggregation because of the close packing of the spherical micelles and the presence of water molecules at the silica micelle interface. The simulated materials were validated by comparing properties such as unit cell size, pore size, pore shape, and wall density to results from experimental X-ray diffraction (XRD), transmission electron microscopy (TEM), density measurements, and Si-29 NMR Quantitative agreement between simulated and experimental nitrogen isotherms was achieved demonstrating the realism of the pore models obtained by the kMC simulations. Our results highlight the importance of a realistic, rough pore surface for the prediction of adsorption at low pressures in these materials.</p

Kinetic Monte Carlo Simulation of the Synthesis of Periodic Mesoporous Silicas SBA‑2 and STAC-1: Generation of Realistic Atomistic Models

SBA-2 and STAC-1 are two related periodic mesoporous silicas (PMSs) that have regular networks of spherical, interconnected pores; the pores are similar in the two materials but the networks differ in their symmetry. The nature of the interconnected network of pores in these materials gives rise to interesting properties related to their potential use in separation processes. In this work, we extend a kinetic Monte Carlo (kMC) technique, originally derived for MCM-41, a simpler PMS, and apply it to mimic the condensation, aggregation, deformation, and calcination stages of the synthesis of SBA-2 and STAC-1. Our simulated synthesis results suggest that the pores are connected through windows formed during micelle aggregation because of the close packing of the spherical micelles and the presence of water molecules at the silica–micelle interface. The simulated materials were validated by comparing properties such as unit cell size, pore size, pore shape, and wall density to results from experimental X-ray diffraction (XRD), transmission electron microscopy (TEM), density measurements, and ²⁹Si NMR. Quantitative agreement between simulated and experimental nitrogen isotherms was achieved demonstrating the realism of the pore models obtained by the kMC simulations. Our results highlight the importance of a realistic, rough pore surface for the prediction of adsorption at low pressures in these materials

Kinetic Monte Carlo Simulation of the Synthesis of Periodic Mesoporous Silicas SBA‑2 and STAC-1: Generation of Realistic Atomistic Models

SBA-2 and STAC-1 are two related periodic mesoporous silicas (PMSs) that have regular networks of spherical, interconnected pores; the pores are similar in the two materials but the networks differ in their symmetry. The nature of the interconnected network of pores in these materials gives rise to interesting properties related to their potential use in separation processes. In this work, we extend a kinetic Monte Carlo (kMC) technique, originally derived for MCM-41, a simpler PMS, and apply it to mimic the condensation, aggregation, deformation, and calcination stages of the synthesis of SBA-2 and STAC-1. Our simulated synthesis results suggest that the pores are connected through windows formed during micelle aggregation because of the close packing of the spherical micelles and the presence of water molecules at the silica–micelle interface. The simulated materials were validated by comparing properties such as unit cell size, pore size, pore shape, and wall density to results from experimental X-ray diffraction (XRD), transmission electron microscopy (TEM), density measurements, and ²⁹Si NMR. Quantitative agreement between simulated and experimental nitrogen isotherms was achieved demonstrating the realism of the pore models obtained by the kMC simulations. Our results highlight the importance of a realistic, rough pore surface for the prediction of adsorption at low pressures in these materials

Kinetic Monte Carlo Simulation of the Synthesis of Periodic Mesoporous Silicas SBA‑2 and STAC-1: Generation of Realistic Atomistic Models

SBA-2 and STAC-1 are two related periodic mesoporous silicas (PMSs) that have regular networks of spherical, interconnected pores; the pores are similar in the two materials but the networks differ in their symmetry. The nature of the interconnected network of pores in these materials gives rise to interesting properties related to their potential use in separation processes. In this work, we extend a kinetic Monte Carlo (kMC) technique, originally derived for MCM-41, a simpler PMS, and apply it to mimic the condensation, aggregation, deformation, and calcination stages of the synthesis of SBA-2 and STAC-1. Our simulated synthesis results suggest that the pores are connected through windows formed during micelle aggregation because of the close packing of the spherical micelles and the presence of water molecules at the silica–micelle interface. The simulated materials were validated by comparing properties such as unit cell size, pore size, pore shape, and wall density to results from experimental X-ray diffraction (XRD), transmission electron microscopy (TEM), density measurements, and ²⁹Si NMR. Quantitative agreement between simulated and experimental nitrogen isotherms was achieved demonstrating the realism of the pore models obtained by the kMC simulations. Our results highlight the importance of a realistic, rough pore surface for the prediction of adsorption at low pressures in these materials