Graphene coated magnetic nanoparticles facilitate the release of biofuels and oleochemicals from yeast cell factories

Engineering of microbial cells to produce high value chemicals is rapidly advancing. Yeast, bacteria and microalgae are being used to produce high value chemicals by utilizing widely available carbon sources. However, current extraction processes of many high value products from these cells are time- and labor-consuming and require toxic chemicals. This makes the extraction processes detrimental to the environment and not economically feasible. Hence, there is a demand for the development of simple, effective, and environmentally friendly method for the extraction of high value chemicals from these cell factories. Herein, we hypothesized that atomically thin edges of graphene having ability to interact with hydrophobic materials, could be used to extract high value lipids from cell factories. To achieve this, array of axially oriented graphene was deposited on iron nanoparticles. These coated nanoparticles were used to facilitate the release of intracellular lipids from Yarrowia lipolytica cells. Our treatment process can be integrated with the growth procedure and achieved the release of 50% of total cellular lipids from Y. lipolytica cells. Based on this result, we propose that nanoparticles coated with axially oriented graphene could pave efficient, environmentally friendly, and cost-effective way to release intracellular lipids from yeast cell factories

Etude expérimentale et modélisation de l'oxydation catalysée de suies Diesel

The objective of this Ph.D. thesis is the development of kinetic models for platinum-ceria-zirconia (Pt/CexZr1−xO2)-catalysed diesel particle filter (DPF) regeneration. Such models have a practical purpose in that they can be used to calculate source terms in 3D flow models, and they also have an intrinsic interest for the understanding of the mechanisms of catalysed soot oxidation. The core of this kinetic analysis consists in estimating Arrhenius parameters of a number of detailed reaction steps by fitting calculated curves to experimental ones. In doing so, the aim is not only to understand the roles of the different reactants, but also to investigate the efficacy and limitations of the modelling procedure for gas-solid heterogeneous reactions. Principal among the examined aspects is the feasibility of attributing physically meaningful values to individual parameters in large reaction mechanisms. The problem is approached by fitting one "subset"of reaction steps at a time. This procedure is illustrated by means of the cases of soot oxidation by NO, NO2 and/or O2, NO oxidation catalysed by ceria-based catalysts and soot oxidation catalysed by Pt/CexZr1−xO2. Interesting insights are gained into the mechanisms of these reactions, since the kinetics had often not been analysed thoroughly in the relevant literature. The fitting approach is shown to be effective as it allows for reproduction of several key species profiles in each of a number of experiments. Experiments used for these kinetic studies are temperature programmed tests in a fixed bed reactor, many of which were performed during the course of the study and data concerning others taken from the literature. In order to extract kinetic parameters from the temperature programmed data, a reactor model describing gas flow through a bed of particles and a mean field model of soot and catalyst surface chemistry are developed. The role of soot structure, ceria-zirconia composition/structure and soot/catalyst ratio on reaction are considered. Parameters used to deal with their effects are estimated.L'objectif de cette thèse est de d'evelopper des modèles cinétiques pour la régénération des filtres à particules Diesel (FaP), basés sur la catalyse par des formulations du type platine-cérine-zircone (Pt/CexZr1−xO2). L'intérêt pratique de ce type de modèle est lié à son utilité dans le calcul de termes sources chimiques dans des modèles 3D, et à la possibilité d'étudier le mécanisme réactionnel de l'oxydation catalysée de la suie. Au coeur de cette analyse cinétique se situe l'estimation des paramètres d'Arrhenius pour un ensemble d'étapes réactionnelles, en ajustant les courbes théoriques (calculées) à celles obtenues expérimentalement. Ce faisant, l'objectif n'est pas seulement de comprendre le rôle des différents réactifs, mais aussi d'explorer l'efficacité et les limitations de la modélisation des réactions hétérogènes à l'interface des phases gazeuses et solides. Le défi principal de cette démarche est l'attribution de valeurs physiques pertinents à des paramètres individuels dans un mécanisme réactionnel complexe. Notre stratégie pour aborder ce problème consiste en un ajustement progressif de sous-ensembles des étapes réactionnelles. Pour illustrer cette procédure, nous avons développé trois configurations d'oxydation des suies : i) l'oxydation par O2, NO et/ou NO2, non catalysée ii) l'oxydation par NO2 en présence d'un catalyseur en cérine, et iii) l'oxydation catalysée par Pt/CexZr1−xO2. La cinétique de ces réactions n'a pas été exhaustivement étudiée auparavant, et nos résultats ont apporté une meilleure compréhension de ce phénomène. L'approche d'ajustement s'est démontré justifiée, car elle a permis la reproduction de profils d'espèces-clés dans un ensemble de conditions expérimentales. Les études cinétiques expérimentales ont été menées sous forme de tests en température programmée, dans un réacteur à lit fixe. Une partie de nos données expérimentales a été obtenue directement ainsi, les autres donnée provenant d''etudes publiées par d'autres groupes. Afin de déduire les paramètres cinétiques à partir de ces données, un modèle de réacteur décrivant l'écoulement de gaz à travers un empilement de particules a été construit. Ce modèle comprend un sous-modèle portant sur la surface chimique des suies et du catalyseur, basé sur l'approximation du champ moyen. L'impact de la structure graphitique des suies, la composition/structure de la cérine-zircone et du ratio suie/catalyseur dans la réaction ont été considérés. Les paramètres décrivant leurs effets ont été estimés

Deactivation of Cu/SAPO-34 during low-temperature NH3-SCR

The sensitivity of NH3-SCR activity to water vapour at 70 degrees C is tested for Cu/SAPO-34 (morph.) catalysts. The synthesised Cu/SAPO-34 (morph.) is remarkably susceptible to low-temperature activity loss. After only 3 hat 70 degrees C, the NOx conversion decreases from an initial 87% to 66% at 200 degrees C, after another 9 h to 6%. This deactivation is accompanied by a partial loss of microporous volume, but the SAPO-34 framework remains crystalline. We postulate that a transformation of the active copper sites into an inactive form could be the cause for the deactivation. Regeneration of the catalyst was attempted, but had no impact on activity

Mechanistic study of hydrothermally aged Cu/SSZ-13 catalysts for ammonia-SCR

The impact of hydrothermal ageing on the copper sites, crystalline order and critical reactions of a Cu/SSZ-13 was studied. The investigated catalyst had a low Si/Al ratio of 3.7 and was underexchanged at 65%. We propose that this catalyst had nearly saturated ion exchange positions in the 6-membered ring units (6MR) with copper ions, but still contained a significant amount of protonic sites in the large cages (8MR units). Investigation of a broad range of ageing temperatures (550-850 degrees C) allowed us to observe that no significant number of copper ions moved from the large cages into the 6MR units. Nevertheless, the Cu ions experienced a significant increase in reducibility above ageing temperatures of 700 degrees C. However, these changes appeared not to have a large impact on catalyst activity, which was more significantly correlated with long and short-range loss of crystallinity. Thus dealumination occurred at all temperatures above 550 degrees C and was correlated with significantly reduced ammonia storage capacity and ammonia oxidation ability. Low-temperature SCR activity was not much affected below 850 degrees C, but decreased significantly when total collapse of the zeolite framework occurred at this temperature. At ageing temperatures above 750 degrees C, formation of oxidic copper species was observed and correlated partially with increased high-temperature ammonia oxidation capacity, though it is possible that oxidation in parallel occurs on non-oxidic sites in ion-exchange positions. On the other hand, low-temperature ammonia oxidation was shown to occur on ionic copper sites (likely in the 6MR units) and decrease with increasing ageing temperature. We further found some evidence that low-temperature formation of N2O during standard SCR may occur on different sites or via different mechanisms

Ammonia Desorption Peaks Can Be Assigned to Different Copper Sites in Cu/SSZ-13

The purpose of this study is to attribute NH 3 -TPD peaks observed over Cu/SSZ-13 catalysts to different catalytic sites. This is done by comparing a large number of copper loadings, especially below 40% ion exchange, to be able to see effects relevant to sites in both 6-membered and 8-membered rings. We found that intermediate (200–300 \ub0C) and high (400–500 \ub0C) temperature NH 3 -TPD peaks followed similar trends to the copper species in 6-membered and 8-membered rings respectively, as seen by H 2 -TPR and NO-DRIFTS. Thus we propose that these two TPD peaks represent ammonia stored on H and Cu sites in 6 and 8-membered rings, respectively. This assignment is further supported by the finding that the intermediate and high temperature NH 3 -TPD peaks of samples with different Si/Al ratios also follow the same trend. Moreover, we observe that the activation energy for ammonia oxidation is significantly lower for Cu in 6MR compared to Cu in 8MR rings. Graphical Abstract: [Figure not available: see fulltext.]

Volatilisation and subsequent deposition of platinum oxides from diesel oxidation catalysts

In this study, we have reproduced a DOC-upstream-of-SCR configuration in the laboratory, with washcoated model Pt/Al2O3, Pd-Pt/Al2O3and Pd/Al2O3catalysts, as well as a commercial DOC, upstream of an alumina-washcoated core. We studied vapour-phase noble metal poisoning of the alumina core, as noble metal from the model DOC catalysts deposited on the downstream alumina core. The mobile species were predominantly volatile platinum oxides, whereas Pd volatilised in such small traces that it was close or below detection limit by Inductively Coupled Plasma – Sector Field Mass Spectrometry (ICP-SFMS), even when the model DOC had only Pd as active species. Even after volatilisation at temperatures as low as 550 \ub0C, the deposited trace amounts of noble metal were highly active for ammonia oxidation. The deposited platinum appears to be finely dispersed, but when subjected to reaction conditions, it likely undergoes sintering, causing a further increase of the ammonia oxidation ability, which will affect the extent of poisoning in a real exhaust aftertreament system. We investigated the dependence of volatilization on temperature, and, as predicted, found it to be exponential. Exposure to increasing temperatures causes different degrees of sintering of the noble metal particles and we found qualitative evidence that sintering decreases the amount of volatilisation. Adding a small amount of Pd (Pd:Pt = 0.5:1) to the catalyst had no effect on volatilisation. However, larger Pd concentrations (Pd:Pt = 1:1 or 2:1) decrease volatilisation. The results for the model DOCs were confirmed by volatilisation from a commercial DOC, where in fact the capturing core exhibited even higher ammonia oxidation ability compared to those downstream of the model DOCs, after evaporation at 700 \ub0C

Influence of phosphorus on Cu-SSZ-13 for selective catalytic reduction of NOx by ammonia

The influence of phosphorus on Cu-SSZ-13 NH3-SCR catalysts was investigated in order to reveal the deactivation behavior of Cu-SSZ-13 in the presence of phosphorus-containing poisons in the exhaust of diesel engines. The phosphorus-poisoning was simulated by treating the Cu-SSZ-13 catalysts with (NH4)(2)HPO4 aqueous solution using incipient wetness impregnation method. The focus of the study was the effect of phosphorous on the different reactions occurring on the SCR catalyst, including ammonia oxidation, NO oxidation and standard SCR using monolith catalysts. Moreover, characterization such as ICP-SFMS, N-2-physisorption, and NH3-TPD were employed for the evaluation of the physical and chemical properties of the P-impregnated catalysts. Physically blocking of pores and poisoning of acidic sites were observed on the P-impregnated catalysts. In addition, we observed that phosphorus severely suppressed ammonia oxidation and NO oxidation, while its impact on standard SCR reaction was nearly negligible below 300 degrees C. Interestingly, a promotive effect was found at higher temperatures, likely due to the severely inhibiting effect on NH3 oxidation caused by the formation of copper phosphates in the large cages (i.e. 8-membered rings) of Cu-SSZ-13