Douglas B. Galloway

n-Butane isomerization on sulfated zirconia: active site heterogeneity and deactivation

Abstract The fast deactivation of sulfated zirconia (SZ) has limited its use in commercial processes such as n-butane isomerization. In order to investigate this deactivation, steady-state isotopic transient kinetic analysis (SSITKA) was utilized to study in situ changes in surface kinetic parameters for n-butane isomerization on a widely studied SZ at 150°C. Approximately 20% of the sulfate species was found to be n-butane adsorption sites, but only 1–2% of the sulfate species appeared to adsorb active surface reaction intermediates. The decrease in catalytic activity during deactivation could be attributed to the loss of active sites. The change in TOF ITK ∗ (TOF based on an average residence time of active surface intermediates) and the regeneration characteristics of the SZ catalyst suggest a possible active site heterogeneity. It appears that the high initial activity and the fast deactivation for TOS ≤100 min were mainly due to the presence and deactivation of the more active sites, respectively. Following the loss of the more active sites, the less active sites provided the majority of the catalytic activity observed for TOS ≥100 min . The less active sites appeared to be more easily regenerated than the more active sites as the catalytic activity at TOS ≥100 min was recovered following regeneration at 315°C. Loss of active sites due to sulfur loss or migration seems unlikely. Site blockage by coke/oligomer formation appeared to be a significant contributor for catalyst deactivation for n-butane isomerization on SZ. The impact of sulfur reduction on catalyst deactivation cannot be ruled out at this point.

n‐butane isomerization on sulfated zirconia: isotopic transient kinetic analysis of reaction at the site level

AbstractBy using SSITKA (steady‐state isotopic transient kinetic analysis), n‐butane (n‐C4) isomerization on sulfated zirconia (SZ) has been studied for the first time at the site level. Accurate measures of the average residence time and the concentration of the most active surface intermediates leading to isobutane (iso‐C4) were able to be determined. As has previously been observed, a fast initial deactivation of the catalyst followed by a slow steady‐state deactivation was observed over 400 min time‐on‐stream (TOS). It was shown that even though a large amount (∼100 μmol/g) of n‐C4

Effect of Ca2+ exchange on adsorption of N2-O2 mixtures by NaCaX zeolite

\left( {N_{n - C4} } \right)

Isotopic Transient Study of Multicomponent N2 and O2 Adsorption on CaX Zeolite

was adsorbed on the catalyst, the concentration of active surface intermediates leading to iso‐C4

Selective aromatics disproportionation/transalkylation catalyst

\left( {N_{iso - C4}^* } \right)

METHODS OF AND APPARATUSES FOR UPGRADING A HYDROCARBON STREAM INCLUDING A DEOXYGENATED PYROLYSIS PRODUCT

was only ∼10 μmol/g at 30 min TOS. The continuous decrease in