Membrane protein channels employed as stochastic sensors offer large signal-to-noise ratios and high specificity in single molecule binding measurements. Stochastic events in a single ion channel system can be measured using current time traces, which are straightforward to analyze. Signals arising from measurement using multiple ion channels are more complicated to interpret. We show that multiple independent ion channels offer improved detection sensitivity compared to single channel measurements and that increased signal complexity can be accounted for using binding event frequency. More specifically, the leading edge of binding events follows a Poisson point process, which means signals from multiple channels can be superimposed and the association times (between each binding event leading edge), allow for sensitive and quantitative measurements. We expand our calibration to high ligand concentrations and high numbers of ion channels to demonstrate that there is an upper limit of quantification, defined by the time resolution of the measurement. The upper limit is a combination of the instrumental time resolution and the dissociation time of a ligand and protein which limits the number of detectable events. This upper limit also allows us to predict, in general, the measurement requirements needed to observe any process as a Poisson point process. The nanopore-based sensing analysis has wide implications for stochastic sensing platforms that operate using multiple simultaneous superimposable signals.

The monomolecular cracking rates of propane and n-butane over MFI, CHA, FER and TON zeolites were determined simultaneously with the coverage of active sites at reaction condition using IR operando spectroscopy. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. The results show that the zeolite confinement mediates enthalpy-entropy trade-offs only at the adsorbed state, leaving the true activation energy insensitive to the zeolite or alkane structure while the activation entropy was found to increase with the confinement. Hence, relative cracking rates of alkanes within zeolite pores are mostly governed by activation entropy.

Dans cette these, nous avons etudie le craquage monomoleculaire d’alcanes legers (C3-C7) par des zeolithes de structure differentes par spectroscopie IR operando. Cette technique permet de mesurer directement le taux de couverture des sites actifs par l’alcane ainsi que les vitesses intrinseques de craquage monomoleculaire. Ces donnee peuvent ensuite etre utilisees pour determiner la thermodynamique de l’adsorption (〖∆H〗_ads and 〖∆S〗_ads) et les parametres cinetiques intrinseques (E_a and 〖∆S〗^‡), permettant ainsi d’etablir l’origine des variations des vitesses apparentes de craquage avec la taille de l’alcane ou la taille des pores de la zeolithe. Notre etude montre que les ces variations de vitesses apparentes sont essentiellement determinees par l’entropie d’activation (〖∆S〗^‡), tandis que l’energie d’activation est pratiquement constante. Les parametres d’adsorption ont un role negligeable dans ces variations de vitesses apparentes en raison de phenomene de compensation entropie-enthalpie. Enfin, nous avons mis en evidence une distribution symetrique des produits de reaction qui n’est pas simplement explicable par les mecanismes couramment admis impliquant des carbocations a 3 centres. Ceci nous a conduits a proposer un mecanisme alternatif concerte. Enfin, l’influence de la temperature sur la thermodynamique de l’adsorption, questionnee par des etudes de simulation recentes, a ete examinee par une approche experimentale couplant l’ATG et la spectroscopie IR (AGIR), permettant de distinguer les deux types d’interaction faibles des alcanes avec les zeolithes (van der Waals vs. Liaison hydrogene). Aucune influence de la temperature sur les fonctions thermodynamiques de l’adsorption.

The coverage of H-MFI zeolite acid sites by light alkanes (C-3-C-7) at monomolecular cracking reaction conditions was determined using infrared operando spectroscopy. Under such conditions, alkane adsorption through H-bonding leads to a fully reversible perturbation of the zeolite nu OH band at 3600 cm(-1). This was used to assess the coverage at various temperatures and pressures, allowing for the determination of the adsorption thermodynamic parameters at reaction conditions. The simultaneous determination of apparent monomolecular cracking rate constants allowed for the direct determination of the intrinsic cracking rate constants, activation energies, and activation entropies. These results show that while the coverage of the active sites increases with the alkane size, the differences tend to decrease at high temperature because of entropic effects. The intrinsic activation energy was constant for all alkanes investigated in this study (similar to 190 kJ mol(-1)), lying in the lower range of the values usually derived from alkane adsorption heats and apparent activation energies. The magnitude of the activation entropies obtained in the present study was also lower than those derived from low temperature adsorption measurements, indicating that temperature could increase the entropy of the adsorbed state. However, this decrease was much less dramatic than that predicted by recent state of art simulations. In any case, this operando study confirms that the activation entropy chiefly determines the variations of apparent protolytic cracking rates.

The ultrastable Y zeolite (USY) in fluid cracking catalyst is commonly stabilized by ion-exchange with rare earth (RE) cations. The RE-exchange provides hydrothermal stability to the zeolite by improving surface area retention, as well as inhibiting dealumination, resulting in greater preservation of acid sites. Though La and Ce are commonly used in fluid catalytic cracking (FCC) catalysts, we have observed that the stability of REUSY catalysts improves as the ionic radius of the RE cation decreases. In this paper, we compare the activity and selectivity of REUSY catalysts, stabilized with La and heavy (Ho, Er, and Yb) rare earth cations, the latter having a smaller ionic radius, due to the well-known phenomenon of lanthanide contraction. The experimental data show that a significant improvement in catalytic activity is achieved when RE elements having a smaller ionic radius are used to make the REUSY catalyst. Yttrium is even more effective than the heavier lanthanides in stabilizing Y-zeolite, leading to higher cracking activity and gasoline selectivity under a variety of deactivation conditions. These benefits of yttrium exchange does not only result from a larger resistance to dealumination, but also to an increase of the catalyst intrinsic cracking activity, which may be explained by changes in the adsorption of hydrocarbons at the active sites. Examples of commercial applications of yttrium-based FCC catalysts are given.

Catalagram 102 Fall 2007 nvironmental regulations have caused refiners to lower specifications on the sulfur content of motor fuels. Because FCC gasoline contributes up to 90 % of the sulfur to the gasoline pool, this has highlighted the importance of reducing sulfur directly in the FCC unit. Grace Davison has been providing catalysts and additives that reduce FCC gasoline sulfur by up to 45% to the refining industry for over 10 years. These technologies have been proven in over 80 units worldwide and include both additive technologies D-PriSM and GSR-5, and complete catalyst systems, such as SuRCA and the newest catalyst system Neptune.

The interaction and reactivity of model sulfur compounds with gasoline sulfur reduction additives based on Zn-, Na-, and F-doped γ-Al2O3 have been investigated by in situ and operando infrared spectroscopy and microactivity tests. While gasoline sulfur reduction additives selectively crack tetrahydrothiophene (THT) into H2S and butadiene they are inactive toward thiophene. When blended with a fluid catalytic cracking (FCC) catalyst, gasoline sulfur reduction additives do reduce (alkyl)thiophene contents in gasoline. There is a synergy between the FCC catalyst and the gasoline sulfur reduction additive leading to sulfur reduction. Under actual FCC conditions, Al2O3-based gasoline sulfur reduction additives reduce thiophenic compounds by decomposing (alkyl)THT formed via hydrogen transfer on the FCC catalyst. A balance between acid and base properties is required for an optimum activity of the additive, suggesting that THT cracking occurs on Lewis acid–base pairs through successive E2 eliminations.