On the enhancing effect of Ce in Pd-MOR catalysts for NOx CH4-SCR: a structure-reactivity study

The effect of palladium and cerium species on the selective catalytic reduction (SCR) of NOx using methane as reductant (NOx CH4-SCR) has been investigated using Pd-HMOR and PdCe-HMOR system. The catalysts have been characterised by H2-TPR, DRS UV–Vis, TEM/EDS and FTIR using CO and pyridine as probe molecules. The oxidation of NO and CH4-SCR catalytic tests have been conducted using monometallic and bimetallic formulations.Above 0.3 wt.% Pd, the increase in Pd loading leads to a decrease in NOx selectivity towards N2, with the formation of N2O, and a decrease in the CH4 selectivity towards SCR, due to CH4 direct combustion. H2-TPR and FTIR-CO studies indicate that palladium is stabilised as Pd2+ in ion-exchange position, probably in two different sites within the MOR framework.The addition of cerium to Pd-HMOR enhances its catalytic performance for NOx CH4-SCR. With 1 wt.% Ce, both NOx conversion into N2 and CH4 selectivity towards SCR have increased. Small CeO2 clusters interacting with palladium are likely to play a major role in this catalytic reaction. The number of such species increases up to Ce loading of ca. 2 wt.%. However, above 3 wt%, NOx conversion values decrease with Ce loading, which is attributed to the formation of bulk CeO2 species not interacting with palladium

On the enhancing effect of Ce in Pd-MOR catalysts for NOx CH4-SCR: a structure-reactivity study

The effect of palladium and cerium species on the selective catalytic reduction (SCR) of NOx using methane as reductant (NOx CH4-SCR) has been investigated using Pd-HMOR and PdCe-HMOR system. The catalysts have been characterised by H2-TPR, DRS UV–Vis, TEM/EDS and FTIR using CO and pyridine as probe molecules. The oxidation of NO and CH4-SCR catalytic tests have been conducted using monometallic and bimetallic formulations. Above 0.3 wt.% Pd, the increase in Pd loading leads to a decrease in NOx selectivity towards N2, with the formation of N2O, and a decrease in the CH4 selectivity towards SCR, due to CH4 direct combustion. H2-TPR and FTIR-CO studies indicate that palladium is stabilised as Pd2+ in ion-exchange position, probably in two different sites within the MOR framework. The addition of cerium to Pd-HMOR enhances its catalytic performance for NOx CH4-SCR. With 1 wt.% Ce, both NOx conversion into N2 and CH4 selectivity towards SCR have increased. Small CeO2 clusters interacting with palladium are likely to play a major role in this catalytic reaction. The number of such species increases up to Ce loading of ca. 2 wt.%. However, above 3 wt%, NOx conversion values decrease with Ce loading, which is attributed to the formation of bulk CeO2 species not interacting with palladium

Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide

The results of both chemical and XPS analysis pointed out that desilication of highly siliceous ZSM-5 of Si/Al = 164 was more effective in the surface zone than in the bulk, contrary to zeolite ZSM-5 of Si/Al = 31.6. According to the IR studies in parent zeolite the concentration of protonic sites was very close to the concentration of Al indicating that all Al atoms can form Si-OH-Al. The results of our quantitative IR studies strongly support the realumination thesis, i.e. some Al atoms extracted in basic solutions are subsequently reinserted forming new acidic hydroxyls. In desilicated zeolites all Al atoms were able to form protonic sites, however part of them dehydroxylated during the activation of zeolite producing Lewis acid sites according to the stoichiometry: one protonic site was transformed into one Lewis site. Low temperature nitrogen adsorption revealed that the alkaline treatment of highly siliceous zeolite with 0.2 M NaOH/TBAOH mixture produced mesopores of smaller diameter and narrower pore size distribution than in the case of zeolite of medium Si/Al ratio. This result can be explained by low concentration of Al which similarly as TBA(+) cations plays the role of pore directing agents (PDA). Contrary to TEA(+), the presence of Al in desilication mixture, led to the formation of larger pores. Therefore, in highly siliceous zeolite TBA(+) played dominant role as PDA producing narrower pores. Highly siliceous zeolite with uniform distribution of relatively narrow pores may be useful catalyst or catalyst support. The influence of desilication temperature on porosity development was also investigated. The increase of desilication temperature from 338 to 353 K resulted in both more extensive demetalation (more Si and Al is extracted) and the distinct increase of the volume and surface of mesopores. Both lower concentration of protonic sites and higher concentration of Lewis sites confirmed partial zeolite destruction upon desilication at elevated temperature. The experiments of pivalonitrile sorption followed by IR spectroscopy showed a significant increase of accessibility of acid sites to bulky pivalonitrile molecules. (C) 2012 Elsevier Inc. All rights reserved.The research was partially carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (Contract No. POIG.02.01.00-12-023/08).Sadowska, K.; Góra-Marek, K.; Drozdek, M.; Kustrowski, P.; Datka, J.; Martínez-Triguero, J.; Rey Garcia, F. (2013). Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide. Microporous and Mesoporous Materials. 168:195-205. https://doi.org/10.1016/j.micromeso.2012.09.033S19520516

Entschlüsselung des Kieselsäure/Silan-Reaktionsmechanismus zur Entwicklung von Reifen mit geringem Rollwiderstand: Teil 2 - Übertragung der Ergebnisse aus den Modelluntersuchungen auf die Praxis

Mit organischen Silanen lassen sich unter kontrollierten Mischungsbedingungen Laufflächenformulierungen herstellen, die den Rollwiderstand von Reifen verringern. Bifunktionale Organosilane können sowohl mit der Kieselsäureoberfläche als auch mit dem Polymer reagieren. Kieselsäure-Verbindungen stellen jedoch bei der Verarbeitung eine Herausforderung dar: Der Kneter fungiert nicht nur als Mischer sondern auch als chemischer Reaktor, weil das Silan während des Mischens chemisch an die Oberfläche der Kieselsäure gebunden werden muss. Die Reaktion zwischen Kieselsäure und Silan verläuft sehr komplex und ist noch nicht in allen Einzelheiten verstanden. Eine bessere Kenntnis des Reaktionsmechanismus könnte Reifenherstellern helfen, den Mischvorgang effizienter zu kontrollieren. Mittels Operando-IR-Spektroskopie während der ­Reaktion lässt sich der Reaktionsmechanismus entschlüsseln

Deciphering the silica/silane reaction mechanism for the development of a new generation of low rolling resistance: Part 2 – Transfer of results from model examinations into practice

By use of suitable organic silanes and controlled mixing conditions, silica/silane systems have proven to be well suited for tire tread formulations with reduced rolling resistance. The bifunctional organosilane is able to react with the silica surface as well as with the polymer. However, silica compounds still present considerable difficulties in processing. The kneader is not only a mixing aggregate but has to fulfill the role of a chemical reactor. It is known from former studies, that the reaction between the silica and the silane is complex. It is up to now not sufficiently understood. Therefore, a better understanding would help many tire producers to control the mixing process more efficiently. Part 1 has shown how Operando IR spectroscopy can be employed to decipher the reaction mechanism. In part 2 the method is used to investigate the reaction of several silica samples with different silanol group densities. Molecular modelling has been used in order to understand the sterical aspects of the reaction. The gained knowledge was used to develop two new silica/silane systems for passenger car tire treads. Their properties in tire treads have been investigate

Unraveling the mechanism of catalytic reactions through combined kinetic and thermodynamic analyses: Application to the condensation of ethanol

SSCI-VIDE+ING+FRMInternational audienceThe combination of kinetic and thermodynamic analyses can provide an in-depth knowledge of the crucial steps of catalyzed reactions. Earlier examples are recalled to stress how a reaction mechanism can be supported or rejected based on trivial reactant and product concentration analyses. The method is then applied to the important reaction of alcohol condensation, the so-called Guerbet reaction, which enables converting ethanol, a renewable feedstock, into higher alcohols. Important conclusions regarding the design of ethanol condensation processes can be drawn, as the main reaction mechanism occurring at high temperatures (ca. 350-420 degrees C) appears to be different from that proposed at low temperatures (< 250 degrees C). In the former case, the pathway involving acetaldehyde is negligible, and therefore a multi-step process based on ethanol dehydrogenation followed by acetaldehyde self-aldolization would be irrelevant. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved