High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites

Abstract

The high resolution adsorption isotherms of N 2 (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm 2 ) and for two MFI zeolite with different Al contents (Si/Al = 12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N 2 isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N 2 and Ar isotherms for MFI zeolite (Si/Al = 500) have been measured at temperatures of 77-94 K, from which the differential adsorption energies of N 2 and Ar are calculated. The interaction of N 2 with channel surface of MFI zeolite is greater than that of Ar in the range of α s = 0.1-0.7. The hystereses are detected for the N 2 isotherm in p/p o = 0.1-0.3 at 77.4 K and for the Ar isotherm in p/p o = 3 × 10 −4 -2 × 10 −3 at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.

Determination of the Exact Microporous Volume and BET Surface Area in Hierarchical ZSM-5

“…Solution 1 was prepared in a polypropylene reactor with stirring bar in which 10 mL of TPAOH were diluted in 6 mL of distilled water. 16 The sorbate pressure was then increased step by step (interval of 0.005 mbar for low relative pressures) in order to obtain the entire adsorption isotherm. For each uptake, the mass change was recorded as function of time.…”

High resolution N2 adsorption isotherms by graphitized carbon black and nongraphitized carbon black – αs-Curves, adsorption enthalpies and entropies

“…p/p°= 10 À9 ) [5,6]. The first purpose of the present work is to determine the detailed standard a s data of N 2 at 77.4 K by graphitized carbon blacks (GCB-I, GCB-II) and nongraphitized carbon blacks (NGCB) from the extremely low relative pressures (p/p°= 5 Â 10 À8 ), whose relative pressures corresponds to a s = 0.002 or h = 0.01.…”

Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen

“…It is well known that nitrogen at 77 K in silicalite-1 and highly siliceous ZSM-5 shows an unusual step accompanied with hysteriesis in the pre-capillary condensation range, typically from P/Po = 0.1-0.2. This interesting phenomena is still not completely understood but it has been discussed that the hysteresis loop and the associated steps reflect a transition from a disordered (liquid-like) adsorbate state to a more ordered (solid-like) adsorbate state or may be associated with a transition of the zeolite from monoclinic to orthorhombic [60][61][62][63][64][65][66]. Hence, these steps are not associated with any filling of empty pore space.…”