Methane Adsorption in Model Mesoporous Material, SBA-15, Studied by Small-Angle Neutron Scattering

Abstract

The understanding of methane adsorption is important for many industrial applications, especially for the shale gas production, where it is critical to understand the adsorption/desorption of methane in pores even as small as a few nanometers. Using small-angle neutron scattering (SANS), we have studied the adsorption of deuterated methane (CD4) into one model mesoporous material, SBA-15, with pore diameter approximately 6.8 nm at the temperature range from 20 to 295 K at low pressure (≈100 kPa). A new scattering model is developed to analyze the SANS patterns of gas adsorption in SBA-15. The surface roughness of the SBA-15 matrix is estimated. The gas adsorption behaviors on the surface regions are extracted from the fitting. The rough surface of the pores is found to retain a large amount of CD4 at the temperature above the capillary condensation temperature (T c). At temperatures below T c, the confined liquid and solid methane are estimated to be less dense than the corresponding bulk liquid and solid methane. Detailed theoretical analysis and experimental verification also show that SANS patterns at temperatures higher than T c are much more sensitive to the change of the excess adsorption, εads, rather than the average density of adsorbed layers commonly used in many studies. The model we establish can be used to analyze future SANS/SAXS data for gas confined in similar model porous materials.

Hierarchical ZSM-5 Zeolite with Enhanced Catalytic Activity for Alkylation of Phenol with Tert-Butanol

“…Zeolites have been applied widely as catalysts due to their high specific surface area and catalytic acidity, which comes from replacing a little silicon dioxide with aluminum oxide. In the past decades, zeolite ZSM-5 has played a significant role in the chemical industry due to some properties, such as exceptional three-dimensional pore structure without cage construction, acid resistance, thermal stability, and hydrophobic resistance [1][2][3][4][5][6][7][8][9][10]. However, the traditional ZSM-5 has only a microporous structure, greatly limiting the applications in the field of catalysis.…”

Investigation of porous materials with large surface heterogeneity using the generalized Porod's scattering law method

“…In this case, all pores are accessible by the guest fluid and the SLD of the solid matrix is not affected by the loaded guest fluid. This situation is common for many synthetic porous materials, such as mesoporous silica or carbon [34,36]. The Porod's scattering from the mesopores is shown at high Q region, if the background and other type of scattering feature are properly subtracted [37].…”

“…GPSLM requires the use of contrast variation. To do contrast variation, SLD of the guest fluid, = , in accessible pores can be changed by mixing hydrogenated and deuterated solvents, such as H2O and D2O, with different ratios [28] for neutron scattering or loading gas with different pressures for both X-ray and neutron scattering [33][34][35]. Thus, the GPSLM can be used for both SAXS and SANS even though we use SANS as the example to demonstrate this method.…”

“…(5). 34 . Therefore, for Case 4, we can determine the specific surface area weighted by the square of the matrix volume fraction at each surface position, i.e.…”

“…In some works,[39] the surface of large domains is called "envelope" surface. As a simple example, the Porod's scattering from the grain boundaries of mesoporous materials shown at low Q region cannot pick up the mesopore structure because the size of mesopores is too small compared with the Porod's scattering length scale L[33,34,40]. Case 3 can be applied to analyze the Porod's scattering region at low Q for a mixture of mesoporous materials composed of different chemical components.…”