N-functionalized carbon nanotubes as solid basic catalysts for biomass conversion

In the view of declining fossil fuel energy resources and rising oil prices, it is necessary to develop new ways to satisfy the energy needs and the production of chemicals. An alternative route is the use of biomass, in fact, it can serve as a sustainable source of renewable fuels and high value chemicals and materials [1-2]. Thus new catalysts need to be developed. In particular basic catalysts will play an important role for many reactions involving biomass transformation such as transesterification, dehydration, aldol condensation, or isomerization reactions, for example [3]. Nitrogen-containing carbon nanotubes (N-MWCNT) appear to be a promising basic catalyst [4]. In fact, in contrast to the existing heterogeneous basic catalysts (such as hydrotalcite, MgO, CaO) they are chemically stable and they do not suffer of problem of leaching. In this work we developed a new route to synthesize N-MWCNTs by grafting different ammines (diethyl-ethylamine, ethylamine and pyrrolidine) on the surface of the MWCNTs. Thus we investigated the potential use of N-MWCNTs as solid catalysts in the transesterification of triglycerides, model reaction for basic catalysts. In particular we study the influence of the basicity of the different amines on the catalytic activity and the stability of the catalysts after recycling reactions

Nitrogen-functionalized carbon nanotubes as a basic catalyst for biomass conversion reactions

Biomass conversion to transportation fuels and chemicals is a growing field of research due to the depletion of fossil fuels feedstock. New catalysts, optimized for carbohydrates conversion, need to be developed. In this context, basic heterogeneous catalysts will play a major role for dehydration, hydrolysis, (trans)esterification, aldol condensation, alkylation or isomerization reactions for example. In contrast to existing basic heterogeneous catalysts, MWCNTs-based catalysts are chemically stable (no leaching) and relatively easy to tailor on a nano- and macro-level (controlled porosity). Therefore, nitrogen-functionalized multiwalled carbon nanotubes (N-MWCNTs) appear to be a promising basic catalyst and catalyst support [1,2]. Unfortunately, the nitrogen concentration, its location in/on the nanotube and the nature of the formed N-containing functional groups are difficult to control by common synthesis techniques like by catalytic chemical vapor deposition (CCVD) or by post-treatments [3]. In addition, it is still unclear which functional groups are required to reach high catalytic activities. Thus, we synthesized N-MWCNTs catalysts by grafting desired N-containing molecules on the MWCNTs’ surface. In order to avoid the drawbacks of the traditional SOCl2 route, a new procedure has been designed. The obtained catalysts have been tested in the transesterification of glyceryl tributyrate, as a model triglyceride for biodiesel synthesi

Carbon Dioxide Methanation for Human Exploration of Mars: A Look at Catalyst Longevity and Activity Using Supported Ruthenium

Overarching Purpose: To design a carbon dioxide methanation/Sabatier reaction catalyst able to withstand variable conditions including fluctuations in bed temperature and feed flow rates for 480 days of remote operation to produce seven tons of methane. Current Study Purpose: Examine supported Ruthenium as a carbon dioxide methanation catalyst to determine the effects support properties have on the active phase by studying activity and selectivity. Objective: The remote operation of the Mars ISRU (In Situ Resources Utilization) lander to produce rocket fuel prior to crew arrival on the planet to power an ascent vehicle. Constraints: Long-term operation (480 days); Variable conditions: Feed gas flow rates, Feed gas flow ratios, Reactor bed temperature

The role and structure of carbonaceous materials in dehydrogenation reactions

The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes is widely studied as a route to the formation of alkenes and di-alkenes, important precursor molecules for synthetic rubbers, plastics and a variety of other products [1,2]. Recent studies have focused on the non-oxidative DH of butane over alumina-supported vanadia catalysts [3-5]. In the present work, we provide a detailed understanding of both the role and structure of coke deposited on VOx/Al2O3 during reaction. A range of characterisation techniques have been employed including the first application of terahertz time domain spectroscopy (THz-TDS) to the study of coke. Complementary THz-TDS characterisation of carbonaceous materials including carbon nanofibres (CNFs) has also been conducted. For such materials THz-TDS spectra can be correlated with their catalytic performance in the oxidative dehydrogenation of ethylbenzene to form styrene

The structure and mechanistic impact of carbon deposits in dehydrogenation reactions

The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes is widely studied as a route to the formation of alkenes and di-alkenes, important precursor molecules for synthetic rubbers, plastics and a variety of other products [1-4]. Recent studies have focused on the non-oxidative DH of butane over alumina-supported vanadia catalysts [5-7]. In the present work, we provide a detailed understanding of both the role and structure of coke deposited on VOx/Al2O3 during reaction. A range of characterisation techniques have been employed including the first application of terahertz time domain spectroscopy (THz-TDS) to the study of coke. Complementary THz-TDS characterisation of carbonaceous materials including carbon nanofibres (CNFs) has also been conducted

Labeling and monitoring the distribution of anchoring sites on functionalized CNTs by atomic layer deposition

The chemical inertness of graphite and, in the case of tubes, of rolled up few layer graphene sheets, requires some degree of “defect engineering” for the fabrication of carbon based heterostructured materials. It is shown that atomic layer deposition provides a means to specifically label anchoring sites and can be used to characterize the surface functionality of differently treated carbon nanotubes. Direct observation of deposited titania by analytical transmission electron microscopy reveals the location and density of anchoring sites as well as structure related concentrations of functional groups on the surface of the tubes. Controlled functionalization of the tubes therefore allows us to tailor the distribution of deposited material and, hence, fabricate complex heterostructures

MOx/CNTs Hetero-Structures for Gas Sensing Applications: Role of CNTs Defects

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Analysis of the structure and chemical properties of some commercial carbon nanostructures

For many years the scientific community has believed in a promising future for carbon nanotubes for various applications in such diverse fields as polymer reinforcement, adsorption, catalysis, electronics and medicine. Industrial production of carbon nanotubes and -fibers and the subsequent availability and decrease of price, have rendered this vision feasible. In the last years, several carbon nanomaterial products have been marketed by major chemical companies. In this work, we present an extensive characterization of a representative set of commercially available carbon nanomaterials. Special focus has been put on their quality, i.e. presence of metal or carbonaceous impurities but also homogeneity and structural integrity. The observations are of importance for subsequent use in catalysis where the presence of impurities or defects in the nanostructure can dramatically modify the activity of the catalytic material

Dosimetric accuracy and radiobiological implications of ion computed tomography for proton therapy treatment planning

Ion computed tomography (iCT) represents a potential replacement for x-ray CT (xCT) in ion therapy treatment planning to reduce range uncertainties, inherent in the semi-empirical conversion of xCT information into relative stopping power (RSP). In this work, we aim to quantify the increase in dosimetric accuracy associated with using proton-, helium- and carbon-CT compared to conventional xCT for clinical scenarios in proton therapy. Three cases imaged with active beam-delivery using an ideal single-particle-tracking detector were investigated using FLUKA Monte-Carlo (MC) simulations. The RSP accuracy of the iCTs was evaluated against the ground truth at similar physical dose. Next, the resulting dosimetric accuracy was investigated by using the RSP images as a patient model in proton therapy treatment planning, in comparison to common uncertainties associated with xCT. Finally, changes in relative biological effectiveness (RBE) with iCT particle type/spectrum were investigated by incorporating the repair-misrepair-fixation (RMF) model into FLUKA, to enable first insights on the associated biological imaging dose. Helium-CT provided the lowest overall RSP error, whereas carbon-CT offered the highest accuracy for bone and proton-CT for soft tissue. For a single field, the average relative proton beam-range variation was  −1.00%, +0.09%, −0.08% and  −0.35% for xCT, proton-, helium- and carbon-CT, respectively. Using a 0.5%/0.5mm gamma-evaluation, all iCTs offered comparable accuracy with a better than 99% passing rate, compared to 83% for xCT. The RMF model predictions for RBE for cell death relative to a diagnostic xCT spectrum were 0.82–0.85, 0.85–0.89 and 0.97–1.03 for proton-, helium-, and carbon-CT, respectively. The corresponding RBE for DNA double-strand break induction was generally below one. iCT offers great clinical potential for proton therapy treatment planning by providing superior dose calculation accuracy as well as lower physical and potentially biological dose exposure compared to xCT. For the investigated dose level and ideal detector, proton-CT and helium-CT yielded the best performance