EMSL and Institute for Integrated Catalysis (IIC) Catalysis Workshop

Within the context of significantly accelerating scientific progress in research areas that address important societal problems, a workshop was held in November 2010 at EMSL to identify specific and topically important areas of research and capability needs in catalysis-related science

Dissecting the steps of CO2 reduction: 2. The interaction of CO and CO2 with Pd/gamma-Al2O3: an in situ FTIR study

Alumina supported Pd catalysts with metal loadings of 0.5, 2.5 and 10 wt% were investigated by in situ FTIR spectroscopy in order to understand the nature of adsorbed species formed during their exposure to CO2 and CO. Exposing the annealed samples to CO2 at 295 K resulted in the formation of alumina support-bound surface species only: linear adsorbed CO 2, bidentate carbonates and bicarbonates. Room temperature exposure of all three samples to CO produced IR features characteristic of both ionic and metallic Pd, as well as bands we observed upon CO2 adsorption (alumina support-bound species). Low temperature (100 K) adsorption of CO on the three samples provided information about the state of Pd after oxidation and reduction. Oxidized samples contained exclusively ionic Pd, while mostly metallic Pd was present in the reduced samples. Subsequent annealing of the CO-saturated samples revealed the facile (low temperature) reduction of PdO x species by adsorbed CO. This process was evidenced by the variations in IR bands characteristic of ionic and metallic Pd-bound CO, as well as by the appearance of IR bands associated with CO2 adsorption as a function of annealing temperature. Samples containing oxidized Pd species (oxidized, annealed or reduced) always produced CO2 upon their exposure to CO, while no CO2-related surface entities were observed on samples having only fully reduced (metallic) Pd. This journal is ??? the Partner Organisations 2014.close0

CHPM2030 Deliverable 2.1: Recommendations for Integrated Reservoir Management

<p>In this report CHPM related practical laboratory work, computer modeling and rock measurements are described, organised and concluded. The main focus was to provide practical recommendations for integrated reservoir management based on laboratory experiments.</p

Nonthermal plasma-assisted catalytic NOx reduction over Ba-Y,FAU: the effect of catalyst preparation

The effects of catalyst preparation on the NOx reduction activity of a series of Ba-Y,FAU zeolites were investigated using a simulated exhaust gas mixture. The introduction of Ba2+ ions into Na-Y,FAU results in a large increase in their nonthermal plasma-assisted NOx reduction activity. The NOx reduction activities of Ba-Y,FAU catalysts were found to increase with increasing Ba2+ concentration in the aqueous ion-exchange solutions, which translated into increased Ba2+/Na+ ratios in the resulting materials. Consecutive ion-exchange procedures at a given Ba2+ concentration in the aqueous solution, however, did not improve the NOx reduction activities of Ba-Y,FAU catalysts; i.e., the activity of the four times ion-exchanged material was the same as that of the one that was ion-exchanged only once. The reaction profiles for all of these Ba-Y,FAU catalysts were the same. In contrast, a significant increase in NOx reduction activity was observed when a 773 K calcination step was implemented after each solution ion exchange. The reaction profile was also altered as a result of the ion-exchange/calci nation cycles. Calcination that followed each ion-exchange step seems to further increase the Ba2+/Na+ ratio in the zeolite, and in turn increases the NOx reduction activities of the catalysts prepared this way. Key differences in Na- and Ba-Y,FAU catalysts were found in NO2 adsorption and TPD experiments. The amount of chemisorbed NO2 is about twice as high in Ba-Y,FAU than in Na-Y,FAU, and Ba-Y,FAU holds NOx much stronger than Na-Y,FAU. Published by Elsevier Incclose273

Ethanol dehydration on gamma-Al2O3: Effects of partial pressure and temperature

Ethanol dehydration was investigated using platelet gamma-Al2O3 over a wide range of reaction temperature (180-300 degrees C) and ethanol partial pressure (0.5-2 kPa) by X-ray diffraction, ethanol Temperature programmed desorption and reactions. The turnover frequencies for commercial and platelet gamma-Al2O3 were almost identical (1.2-1.3 x 10(-2) ethanol/site s) when normalized to the number of ethoxide quantified by ethanol TPD. The desorption barrier of ethoxide was 183.6 kj/mol, similar to the activation barrier of ethylene formation. These results demonstrate that ethoxide is a key intermediate rather than molecular ethanol, possibly suggesting an El mechanism for ethylene formation, consistent with recent spectroscopic studies. Detailed kinetic measurements demonstrate the nature of the species on alumina surface varied with reaction temperature. At low temperature (180 degrees C), the ethanol dimer, one of which would be the ethoxide, saturated the surface, leading to the inhibition of ethylene formation and constant ether formation rates with ethanol pressure. At high temperature (260 degrees C), the ethanol monomer became dominant, consistent with the constant ethylene formation rates and increased ether formation rates with ethanol pressure. The apparent activation energies also changed with reaction temperature and ethanol partial pressure. Especially, the inhibition by ethanol dimer clearly contributed the increased apparent activation barrier at 180 degrees C

Non-thermal plasma-assisted NOx reduction over Na-Y zeolites: the promotional effect of acid sites

The effect of acid sites on the catalytic activities of a series of H+-modified Na-Y zeolites was investigated in the non-thermal plasma assisted NOx reduction reaction using a simulated diesel engine exhaust gas mixture. The acid sites were formed by NH4+ ion exchange and subsequent heat treatment of a NaY zeolite. The catalytic activities of these H+-modified NaY zeolites significantly increased with the number of acid sites. This NOx conversion increase was correlated with the decrease in the amount of unreacted NO2. The increase in the number of acid sites did not change the NO level, it stayed constant. Temperature programmed desorption following NO2 adsorption showed the appearance of a high temperature desorption peak at 453 K in addition to the main desorption feature of 343 K observed for the base Na-Y. The results of both the IR and TPD experiments revealed the formation of crotonaldehyde, resulting from condensation reaction of adsorbed acetaldehyde. Strong adsorptions of both NOx and hydrocarbon species are proposed to be responsible for the higher catalytic activity of H+-modified Na-Y zeolites in comparison to the base NaY material.close1

Elucidating the role of CO in NO storage mechanism on Pd/SSZ-13 with in situ DRIFTS

Pd ion exchanged zeolites emerged as promising materials for the adsorption and oxidation of air pollutants. For low-temperature vehicle exhaust, dispersed Pd ions are able to adsorb NOx even in H2O-rich exhaust in the presence of carbon monoxide. In order to understand this phenomenon, changes in Pd ligand environment have to be monitored in-situ. Herein, we directly observe the activation of hydrated Pd ion shielded by H2O into a carbonyl-nitrosyl complex Pd2+(NO)(CO) in SSZ-13 zeolite. The subsequent thermal desorption of ligands on Pd2+(NO)(CO) complex proceeds to nitrosyl Pd2+ rather than to carbonyl Pd2+ under various conditions. Thus, CO molecules act as additional ligands to provide alternative pathway through Pd2+(NO)(CO) complex with lower energy barrier for accelerating NO adsorption on hydrated Pd2+ ion, which is kinetically limited in the absence of CO. We further demonstrate that hydration of Pd ions in the zeolite is a prerequisite for CO-induced reduction of Pd ions to metallic Pd. The reduction of Pd ions by CO is limited under dry conditions even at a high temperature of 500°C, while water makes it possible at near RT. However, the primary NO adsorption sites are Pd2+ ions even in gases containing CO and water. These findings clarify additional mechanistic aspects of the passive NOx adsorption (PNA) process and will help extend the NOx adsorption chemistry in zeolite-based adsorbers to practical applications

Mechanism of CO2 Hydrogenation on Pd/Al2O3 Catalysts: Kinetics and Transient DRIFTS-MS Studies

The hydrogenation of CO2 was investigated over a wide range of reaction conditions, using two Pd/-Al2O3 catalysts with different Pd loadings (5% and 0.5%) and dispersions (???11% and ???100%, respectively). Turnover rates for CO and CH4 formation were both higher over 5% Pd/Al2O3 with a larger average Pd particle size than those over 0.5% Pd/Al2O3 with a smaller average particle size. The selectivity to methane (22-40%) on 5% Pd/Al2O3 was higher by a factor of 2-3 than that on 0.5% Pd/Al2O3. The drastically different rate expressions and apparent energies of activation for CO and CH4 formation led us to conclude that reverse water gas shift and CO2 methanation do not share the same rate-limiting step on Pd and that the two pathways are probably catalyzed at different surface sites. Measured reaction orders in CO2 and H2 pressures were similar over the two catalysts, suggesting that the reaction mechanism for each pathway does not change with particle size. In accordance, the DRIFTS results reveal that the prevalent surface species and their evolution patterns are comparable on the two catalysts during transient and steady-state experiments, switching feed gases among CO2, H2, and CO2 + H2. The DRIFTS and MS results also demonstrate that no direct dissociation of CO2 takes place over the two catalysts and that CO2 has to first react with surface hydroxyls on the oxide support. The thus-formed bicarbonates react with dissociatively adsorbed hydrogen on Pd particles to produce adsorbed formate species (bifunctional catalyst: CO2 activation on the oxide support and H2 dissociation on the metal particles). Formates near the Pd particles (most likely at the metal/oxide interface) can react rapidly with adsorbed H to produce CO, which then adsorbs on the metallic Pd particles. Two types of Pd sites are identified: one has a weak interaction with CO, which easily desorbs into gas phase at reaction temperatures, whereas the other interacts more strongly with CO, which is mainly in multibound forms and remains stable in He flow at high temperatures, but is reactive toward adsorbed H atoms on Pd leading eventually to CH4 formation. 5% Pd/Al2O3 contains a larger fraction of terrace sites favorable for forming these more multibound and stable CO species than 0.5% Pd/Al2O3. Consequently, we propose that the difference in the formation rate and selectivity to CH4 on different Pd particle sizes stems from the different concentrations of the reactive intermediate for the methanation pathway on the Pd surface. &amp;#169; 2015 American Chemical Societyclose0