1,721,113 research outputs found
Nanostructured solid/liquid acid catalysts for glycerol esterification: the key to convert liability into assets
Full text linkOwing to the growing concerns about the dwindling fossil fuel reserves, increasing energy demand, and climate emergency, it is imperative to develop and deploy sustainable energy technologies to ensure future energy supply and to transition to the net-zero world. In this context, there is great potential in the biorefinery concept for supplying drop in biofuels in the form of biodiesel. Biodiesel as a fuel can certainly bridge the gap where electrification or the use of hydrogen is not feasible, for instance, in heavy vehicles and in the farm and marine transportation sectors. However, the biodiesel industry also generates a large amount of crude glycerol as the by-product. Due to the presence of several impurities, crude glycerol may not be a suitable feedstock for all high-value products derived from glycerol, but it fits well with glycerol esterification for producing glycerol acetins, which have numerous applications. This review critically looks at the processes using nanostructured solid/liquid acid catalysts for glycerol esterification, including the economic viability of the scale-up. The homogeneous catalysts reviewed herein include mineral acids and Brønsted acidic ionic liquids, such as SO3H-functionalized and heteropoly acid based ionic liquids. The heterogeneous catalysts reviewed herein include solid acid catalysts such as metal oxides, ion-exchange resins, zeolites, and supported heteropoly acid-based catalysts. Furthermore, the techno-economic analysis studies have shown the process to be highly profitable, confirming the viability of glycerol esterification as a potential tool for economic value addition to the biorefinery industry.<br/
Structure sensitivity of Cu supported on manganese oxide catalysts in levulinic acid hydrogenation
Full text linkDifferent synthesis methods were used to prepare a series of size-controlled copper nanoparticles supported on manganese oxide octahedral molecular sieve (OMS-2) catalysts. All Cu/OMS-2 catalysts, with average Cu nanoparticle sizes prepared in the range of 2-22 nm, were thoroughly characterised using X-ray diffraction (XRD), N2 sorption, H2 temperature programmed reduction (TPR), transmission electron microscopy (TEM), and ICP-OES elemental analyses. The catalytic activity of the size-controlled Cu/OMS-2 catalysts was investigated in liquid phase hydrogenation of levulinic acid as a model reaction to evaluate the nanoparticle size dependance and structure-activity relationship. The catalytic activity studies showed that the catalyst performance depends greatly on the catalyst preparation methodology and Cu nanoparticle size. Complete conversion of levulinic acid with a high γ-valerolactone yield, >99%, was observed using Cu/OMS-2 catalysts prepared by the precipitation-deposition (Cu nanoparticle size 2-3 nm) method. In comparison to wet-impregnated catalysts (Cu particle size 20-22 nm), the improved performance of precipitation-deposition catalysts was mainly attributed to the well-distributed, smaller Cu nanoparticles. The influence of Cu nanoparticle size is correlated with the turnover frequency (TOF, h−1) for levulinic acid conversion, indicating the structure sensitivity of the levulinic acid hydrogenation reaction.</p
Mechanochemically engineered CaO-CeO<sub>2</sub> dual-function catalysts for sustainable glycerol carbonate production without solvents
Full text linkUpgrading biorefinery-derived waste such as glycerol to fuel-additives and high-value products is essential to further enhance the productivity, profitability, and circularity of the biorefinery concept to achieve a green and sustainable net-zero world. This study explores the catalytic conversion of glycerol into glycerol carbonate using calcium oxide–cerium oxide (CaO–CeO2) dual-function catalytic materials. Herein, a clean and efficient approach was developed to synthesize CaO–CeO2 materials using a green mechanochemical method and then utilize these as catalyst in sustainable and solvent-free synthesis of glycerol carbonate to enhance the circular economy of biorefineries while reducing their carbon footprint. The catalysts were comprehensively characterized using XRD, FTIR, ICP, N2 sorption, CO2-TPD, and SEM/EDS analyses and evaluated for their catalytic activity. Among the catalysts studied, 40 wt % CaO–CeO2 exhibited the highest catalytic activity, achieving 95% glycerol conversion and 99% selectivity to glycerol carbonate under optimized conditions (10 wt % catalyst loading relative to glycerol, 90 °C, 60 min, and a glycerol/ DMC molar ratio of 1:3). This catalyst showed excellent reusability, maintaining high conversion over four cycles. The transesterification reaction followed irreversible second-order reaction kinetics with an activation energy of 46.9 kJ mol–1. The synergistic interplay between the basic sites of the Ca2+–O2– pair and the oxygen vacancies in the CeO2 matrix at the CaO–CeO2 interface work in tandem to enhance the catalytic activity for glycerol carbonate production. We have developed a highly efficient, cost-effective, and environment-friendly approach for the sustainable production of glycerol carbonate from glycerol.<br/
α-Alkylation of Aliphatic Ketones with Alcohols: Base Type as an Influential Descriptor
Full text linkCurrent global challenges associated with energy security and climate emergency, caused by the combustion of fossil fuels (e.g., jet fuel and diesel), necessitate the accelerated development and deployment of sustainable fuels derived from renewable biomass-based chemical feedstocks. This study focuses on the production of long-chain (straight and branched) ketones by direct α-alkylation of short chain ketones using both homogenous and solid base catalysts in water. Thus, produced long-chain ketones are fuel precursors and can subsequently be hydrogenated to long-chain alkanes suitable for blending in aviation and liquid transportation fuels. Herein, we report a thorough investigation of the catalytic activity of Pd in combination with, (i) homogenous and solid base additives; (ii) screening of different supports using NaOH as a base additive, and (iii) a comparative study of the Ni and Pd metals supported on layered double oxides (LDOs) in α-alkylation of 2-butanone with 1-propanol as an exemplar process. Among these systems, 5%Pd/BaSO4 with NaOH as a base showed the best results, giving 94% 2-butanone conversion and 84% selectivity to alkylated ketones. These results demonstrated that both metal and base sites are necessary for the selective conversion of 2-butanone to alkylated ketones. Additionally, amongst the solid base additives, Pd/C with 5% Ba/hydrotalcite showed the best result with 51% 2-butanone conversion and 36% selectivity to the alkylated ketones. Further, the screening of heterogenous acid-base catalysts 2.5%Ni/Ba1.2Mg3Al1 exhibited an adequate catalytic
activity (21%) and ketone selectivity (47%)
OMS-2 molecular sieves doped with ceria for the development of new emission control catalyst
Full text linkManganese oxide octahedral molecular sieves (OMS) are microporous, inorganic nanostructures. Manganese oxides with cryptomelane type structures (OMS-2), has a one-dimensional tunnel structure composed of edge shared MnO6 octahedra that form a 2 x 2 arrangement. [1] OMS-2 materials are hydrophobic and hence have improved hydrolytic stability under oxidation conditions. The mixed valency in OMS-2 contributes to its highly active and selective catalysis. [2] Functionality of OMS-2 can be further extended by structural incorporation of various dopants. In this work we have synthesized a range of OMS-2 based supports doped with Ce, CeZr and Pt for emission control. Materials often used for emission control applications are precious metals supported on a Ceria Zirconia mixed oxide [3-5]. Currently, one of the main challenges is to provide a catalyst which is active at low temperature, due to the high emissions of combustion engines during cold start cycles [6]. In particular, we have investigated the use of these OMS-2 hybrid catalyst supports for their activity in the oxidation reactions of CO, C3H6 and CH4 and compared with a commercial diesel oxidation catalyst. The new catalyst samples were tested under representing those in the catalytic filter of a light duty diesel vehicle. The effect of doping the OMS-2 support with Ceria and Zirconia have been studied both pre and post loading with 1wt% Pt
Efficacy of mechanochemically prepared ceria–zirconia catalysts in ketonisation of acetic acid
Full text linkThis work presents a comprehensive study on the catalytic and kinetic aspects of the ketonisation of acetic acid, a model volatile fatty acid, using Ce1−xZrxO2 as catalysts. Volatile fatty acids are promising biomass derived feedstock for production of drop-in sustainable aviation fuels through a series of cascade reactions, with ketonisation as the first step followed by aldol condensation and subsequent hydrogenation. A series of Ce1−xZrxO2 catalysts for ketonisation were prepared using a mechanochemical technique of ball milling, and their performance was evaluated for varying Ce/Zr mole ratios. Among the catalysts tested, Ce0.75Zr0.25O2 exhibited the highest conversion and selectivity towards the desired product, acetone. The catalyst characterisation showed the formation of nano-aggregates with an average particle size of 340.8 nm and a specific surface area of 66.2 m2 g−1. The kinetics of the reaction indicated a second-order dependence on acetic acid, while the products (acetone, water, and CO2) exhibited negative orders, suggesting competitive adsorption on the active sites of the catalyst. The activation energy for the reaction was determined to be 103.4 kJ mol−1 suggesting the surface reaction as the rate controlling step. These findings provide valuable insights into the catalytic behaviour and kinetics of the ketonisation reaction
Recent advances in processes and catalysts for glycerol carbonate production via direct and indirect use of CO<sub>2</sub>
Full text linkGlycerol can be utilised as a renewable feedstock in several chemical reactions, including carbonation, carbonylation, transesterification, and oxidation. Among the several conversions, the production of glycerol carbonate is environmentally most attractive, as it also utilises CO2 as the carbon source, as C1 feedstock, a key to accelerate the pursuit of decarbonization and the net-zero goals. The glycerol carbonate production can be divided into two main pathways i.e., direct and indirect route based on the utilisation of CO2. There has been much interest in the direct conversion of glycerol with molecular CO2, due to its potential for sustainability and ecological advantages. Moreover, this process could be directly minimising CO2 levels in atmosphere. The indirect pathways involve the utilisation of CO2 as a source for the synthesis of reactants, for instance organic carbonates and urea. These reactants are employed as raw materials in the process of glycerol carbonate production. It is important to note that each reaction route has its own set of advantages and drawbacks. However, the important factor for all processes lies in the high catalytic performance of the suitable catalyst and the optimal reaction conditions to enhance the yield of glycerol carbonate. This review aims to evaluate the recent progress made on the catalyst design and process conditions to produce glycerol carbonate via both the direct and indirect reaction pathways. In each route, the catalytic systems based on the heterogenous catalysts, the reaction condition and catalytic performance are considered. Finally, suggested perspectives for the future direction in glycerol carbonate production focusing on the utilisation of molecular CO2 are presented.<br/
Atomistic simulations on the carbidisation processes in Pd nanoparticles
Full text linkThe formation of interstitial PdCx nanoparticles (NPs) is investigated through DFT calculations. Insights on the mechanisms of carbidisation are obtained whilst the material's behaviour under conditions of increasing C-concentration is examined. Incorporation of C atoms in the Pd octahedral interstitial sites is occurring through the [111] facet with an activation energy barrier of 19.3–35.7 kJ mol−1 whilst migration through the [100] facet corresponds to higher activation energy barriers of 124.5–127.4 kJ mol−1. Furthermore, interstitial-type diffusion shows that C will preferentially migrate and reside at the octahedral interstitial sites in the subsurface region with limited mobility towards the core of the NP. For low C-concentrations, migration from the surface into the interstitial sites of the NPs is thermodynamically favored, resulting in the formation of interstitial carbide. Carbidisation reaction energies are exothermic up to 11–14% of C-concentration and slightly vary depending on the shape of the structure. The reaction mechanisms turn to endothermic for higher concentration levels showing that C will preferentially reside on the surface making the interstitial carbide formation unfavorable. As experimentally observed, our simulations confirm that there is a maximum concentration of C in Pd carbide NPs opening the way for further computational investigations on the activity of Pd carbides in directed catalysis
Bridging the size gap between experiment and theory: large-scale DFT calculations on realistic sized Pd particles for acetylene hydrogenation
No full textMetal nanoparticles, often supported on metal oxide promoters, are a cornerstone of heterogeneous catalysis. Experimentally, size effects are well-established and are manifested through changes to catalyst selectivity, activity and durability. Density Functional Theory (DFT) calculations have provided an attractive way to study these effects and rationalise the change in nanoparticle properties. However such computational studies are typically limited to smaller nanoparticles (approximately up to 50 atoms) due to the large computational cost of DFT. How well can such simulations describe the electronic properties of the much larger nanoparticles that are often used in practice? In this study, we use the ONETEP code, which is able to achieve more favourable computational scaling for metallic nanoparticles, to bridge this size gap. We present DFT calculations on entire Pd and Pd carbide nanoparticles of more than 300 atoms (approximately 2.5 nm diameter), and find major differences in the electronic structure of such large nanoparticles, in comparison to the commonly investigated smaller clusters. These differences are also manifested in the calculated chemical properties such as adsorption energies for C2H2, C2H4 and C2H6 on the pristine Pd and PdC x nanoparticles which are significantly larger (up to twice in value) for the ∼300 atoms structures. Furthermore, the adsorption of C2H2 and C2H4 on PdC x nanoparticles becomes weaker as more C is introduced in the Pd lattice whilst the impact of C concentration is also observed in the calculated reaction energies towards the hydrogenation of C2H2, where the formation of C2H6 is hindered. Our simulations show that PdC x nanoparticles of about 5% C per atom fraction and diameter of 2.5 nm could be potential candidate catalysts of high activity in hydrogenation reactions. The paradigm presented in this study will enable DFT to be applied on similar sized metal catalyst nanoparticles as in experimental investigations, strengthening the synergy between simulation and experiment in catalysis.</p
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