Effect of substituents and promoters on the Diels–Alder cycloaddition reaction in the biorenewable synthesis of trimellitic acid

An efficient route to produce oxanorbornene, a precursor for the production of bio-based trimellitic acid (TMLA) via the Diels-Alder (DA) reaction of biomass-derived dienes and dienophiles has been proposed by utilizing density functional theory (DFT) simulations. It has been suggested that DA reaction of dienes such as 5-hydroxymethyl furfural (HMF), 2,5-dimethylfuran (DMF), furan dicarboxylic acid (FDCA) and biomass-derived dienophiles (ethylene derivatives e.g., acrolein, acrylic acid, etc.) leads to the formation of an intermediate product oxanorbornene, a precursor for the production of TMLA. The activation barriers for the DA reaction were correlated to the type of substituent present on the dienes and dienophiles. Among the dienophiles, acrolein was found to be the best candidate showing a low activation energy (<40 kJ mol-1) for the cycloaddition reaction with dienes DMF, HMF and hydroxy methyl furoic acid (HMFA). The FMO gap and (IPdiene + EAdienophile)/2 were both suggested to be suitable descriptors for the DA reaction of electron-rich diene and electron-deficient dienophile. Further solvents did not have a significant effect on the activation barrier for DA reaction. In contrast, the presence of a Lewis acid was seen to lower the activation barrier due to the reduction in the FMO gap. © The Royal Society of Chemistry

Study of the "Fast SCR" -like mechanism of H2-assisted SCR of NOx with ammonia over Ag/Al2O3

It is shown that Ag/Al2O3 is a unique catalytic system for H-2-assisted selective catalytic reduction of NOx by NH3 (NH3-SCR) with both Ag and alumina being necessary components of the catalyst. The ability of Ag/Al2O3 and pure Al2O3 to catalyse SCR of mixtures of NO and NO2 by ammonia is demonstrated, the surface species occurring discussed, and a "Fast SCR"-like mechanism of the process is proposed. The possibility of catalyst surface blocking by adsorbed NOx and the influence of hydrogen on desorption of NOx were evaluated by FTIR and OFT calculations

Techno-economic analysis of a biorenewable route to produce trimellitic acid

Present study investigates techno-economic feasibility of trimellitic acid (TMLA) production from a biorenewable precursor 5-hydroxymethyl furfural (HMF) for the first time. A 5 kmol/hr HMF feed rate to produce 99% pure TMLA is considered to provide a roadmap for fixing the minimum sales price of TMLA for significant return on investments and a shorter payback period. The current TMLA sales price varies significantly ($10/kg–$1000/kg) in different markets; depending on the process for TMLA production. Thus, techno-economic feasibility study for TMLA production is investigated considering variable sales price. It is also observed that two distinct reaction routes for TMLA production from HMF are possible and both routes can be profitable even at the minimum sales price of $10/kg. Nevertheless, TMLA production from direct conversion of HMF showed better internal rate of return (IRR) (105.94%) than the one calculated for a two-step process (39.42%). It is also observed that catalyst and raw materials costs are main contributing factor in capital and operating costs, respectively. Thus, cost of feed is varied to study the possible future cases, as HMF cost may decrease with advances in the development of biomass conversion technologies. It is observed that the IRR of the TMLA production plant would further increase significantly by ∼16% if raw material cost is reduced by 10–40% in the future

Mechanistic Insights into the Activity of Mo-Carbide Clusters for Methane Dehydrogenation and Carbon–Carbon Coupling Reactions To Form Ethylene in Methane Dehydroaromatization

Methane dehydrogenation and C–C coupling reactions to form ethylene on two different carbide clusters of molybdenum (Mo₄C₂ and Mo₂C₆) were studied. Density functional theory (DFT) calculations were performed to understand the reactivity of the two clusters, linking it to the overall methane dehydroaromatization (MDA) process. The electronic effect of catalyst reduction procedures and anchoring of the cluster on the zeolite framework was captured in simulations with varying positive charge on the cluster. In general, with one exception, DFT calculations suggested a reduction in dehydrogenation activation energies with more reduced (lesser positive charge) clusters. Similarly, activation barriers for the transfer of a H atom from the carbon to the neighboring Mo site were calculated to be lower on more reduced clusters. In contrast, the coupling reactions of the two CH₃ and the two H atoms on the surface showed a reverse trend. The activation energies of the C–C and the H–H coupling steps were observed to be lower on less reduced (higher positive charge) clusters. On comparing the two (Mo₄C₂ and Mo₂C₆) clusters with similar charges, the activation energies for the first methane dehydrogenation were observed to be of similar value on both clusters for the neutral charge. However, second methane dehydrogenation was calculated to show a significantly higher barrier on the Mo₂C₆ cluster for both neutral and +1 charges. In addition, the CH₃ coupling reaction was facilitated with a relatively lower activation barrier on the Mo₂C₆ cluster as compared to that on the Mo₄C₂ cluster. Thus, Mo₂C₆ sites in the vicinity of the Brønsted acid sites of the zeolite are likely to be more active for the coupling of the two CH₃ species and helpful in MDA. This alluded to the operando experimental findings by Lezcano-González [Angew. Chem., Int. Ed. 2016, 55, 5215−5219], wherein it was suggested that methane might be activated on carbide and oxycarbide species; however, formation of MoC₃-type species on stream was linked directly to MDA

SiO₂‑Encapsulated Ag/WO₃ Nano-architectures for Azoxybenzene Production via Simultaneous Activation of Aniline and Molecular O₂

Nanocomposites Ag/WO3 intercalated within the channels of the silica network have been developed using a surfactant-assisted hydrothermal process. Structural and morphological studies indicated that the material exhibited two-dimensional type enchiladas-like nanoarchitectures. Higher-resolution electron microscopy results demonstrated that twinned Ag nanoparticles supported on WO3 units were embedded within the stacked layers of silica without agglomerating. This unique morphology led to higher dispersion of the Ag/WO3 framework that compelled the availability of more exposed surface-active Ag(111) sites, which triggered the activation of molecular O2 in furnishing a high yield of azoxybenzene, and this phenomenon has been explained in the light of DFT