Surface Area, Pore Volume Distribution, and Acidity in Mesoporous Expanded Clay Catalysts from Hybrid Density Functional Theory (DFT) and Adsorption Microcalorimetry Methods

Abstract

A hybrid density functional theory (DFT) method has been used to interpret the data for the adsorption of nitrogen at 77 K within the porous structure of a sample of synthetic saponite expanded with stable SiO2·TiO2 colloidal particles and dried by different methods. Air drying (AD) favor the formation of structures containing both micro- and mesopores. In contrast, drying with supercritical CO2 (SCD) produces mesoporous solids containing only minor amounts of micropores. In SCD samples, the total PV is more than 5 times higher than in AD samples and their structure is hydrothermally stable after a 5-h exposure to 100% steam at 760 °C. Adsorption microcalorimetry experiments with ammonia indicate that the inclusion of SiO2·TiO2 clusters drastically increases the clay total (B + L) acidity; acid site strength and acid site density is greatest in AD samples. Both the BET and BJH methods underestimate the clay catalyst's surface area and only the DFT method yields reliable surface area and pore volume measurements over the entire micro−meso porosity range investigated.

Microwave synthesis of delaminated acid saponites using quaternary ammonium salt or polymer as template. Study of pH influence

“…The emergence of zeolite as solid acid catalyst brought a lot of benefits (Corma, 1997). However, many reagents in the fine and petrochemical industries were excluded by the microporous structures of zeolites (Occelli et al, 2002).…”

Statistical Optimization for Production of Light Olefins in a Fluidized‐Bed Reactor

“…In addition, both samples showed a sharp uptake at a P/P 0 value of less than 0.1. This behavior indicates the existence of microporous units on the surface of the S34-T-C framework domain [26]. The detailed surface area and pore volume data are summarized in Tab.…”

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

“…Whilst BET allows for multilayers, a significant improvement on Langmuir [57], the filling of micropores is not taken into consideration. Many phosphomolybdate salts consist of significant microporosity [38], therefore surface areas derived from the BET model will differ from the actual area depending upon the porous structure of the solid [58,59]. In addition, the phosphomolybdates typically exhibit small surface areas and it is noted that this introduces error into the BET model [52].…”

“…In addition, the phosphomolybdates typically exhibit small surface areas and it is noted that this introduces error into the BET model [52]. The NLDFT technique has been shown to reliably determine surface areas and pore volumes over the entire micromeso porosity range and offers a substantial increase in accuracy over the BET method [58][59][60][61][62]. Therefore the BET analysis is not suitable for phosphomolybdates and the NLDFT approach is preferred.…”