Ecological responses of periphyton dry mass and epilithic diatom community structure for different atrazine and temperature scenarios

Climate change–induced temperature increase may influence the ecotoxicity of agricultural herbicides such as atrazine and consequently negatively impact aquatic biota. The objective of this study was to assess the effects of increased temperature on the ecotoxicity of atrazine to diatom community structure and stream periphyton load using laboratory microcosm experiments. A natural periphyton community from the Mukwadzi River, Zimbabwe, was inoculated into nine experimental systems containing clean glass substrates for periphyton colonisation. Communities were exposed to 0 µg∙L-1 (control), 15 µg∙L-1 and 200 µg∙L-1 atrazine concentrations at 3 temperature levels of 26°C, 28°C and 30°C. Periphyton dry weight and community taxonomic composition were analysed on samples collected after 1, 2 and 3 weeks of colonisation. A linear mixedeffects model was used to analyse the main and interactive effects of atrazine and temperature on dry mass, species diversity, evenness and richness. Temperature and atrazine had significant additive effects on species diversity, richness and dry mass. As temperature increased, diatom species composition shifted from heat-sensitive species such as Achnanthidium affine to heat-tolerant species such as Achnanthidium exiguum and Epithemia adnata. Increasing temperature in aquatic environments contaminated with atrazine results in sensitive and temperature-intolerant diatoms being eliminated from periphyton communities. Climate change will exacerbate effects of atrazine on periphyton dry mass and diatom community structure.Keywords: ecotoxicology, microcosm, biomonitoring, climate chang

Preparation of Biomass-Derived Furfuryl Acetals by Transacetalization Reactions Catalyzed by Nanoporous Aluminosilicates

Nanoporous aluminosilicate materials efficiently catalyze the formation of furaldehyde dimethyl acetal directly from methanol in high yields and in short reaction times. The facile nature of this reaction has led to the development of a telescoped protocol in which the acyclic acetal is produced in situ and subsequently functions as a substrate for a transacetalization reaction with glycerol to produce the corresponding dioxane and dioxolane products, which are potentially useful biofuel additives. These products are generated in high yield without the requirement for high reaction temperatures of prolonged reaction times, and the aluminosilicate catalysts are operationally simple to produce, are effective with either purified furaldehyde or crude furaldehyde, and are fully recyclable

Continuous flow synthesis of bimetallic AuPd catalysts for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

The production of 2,5‐furandicarboxylic acid (FDCA) from the selective oxidation of 5‐hydroxymethylfurfural (HMF) is a critical step in the production of biopolymers from biomass‐derived materials. In this study, we report the catalytic performance of monometallic Au and Pd, and bimetallic AuPd nanoparticles with different Au:Pd molar ratios synthesised under continuous flow conditions using a millifluidic set‐up and subsequently deposited onto titanium dioxide as the chosen support. This synthetic technique provided a better control over mean particle size and metal alloy composition, that resulted in higher FDCA yield when the catalysts were compared to similar batch‐synthesised materials. A 99 % FDCA yield was obtained with the millifluidic‐prepared AuPd/TiO2 catalyst (Au:Pd molar composition of 75:25) after being calcined and reduced at 200 °C. The heat treatment caused a partial removal of the protective ligand (polyvinyl alcohol) encapsulating the nanoparticles and so induced stronger metal‐support interactions. The catalyst reusability was also tested, and showed limited particle sintering after five reaction cycles

Direct and oxidative dehydrogenation of propane: From catalyst design to industrial application

The direct formation of propene from propane is a well-established commercial process, which based on energy consumption, is environmentally preferred to the current large-scale sources of propene from steam cracking and fluid catalytic cracking. Current sources of propane are mostly non-renewable, but the development of technologies to produce renewable “green” propane are gaining traction, which coupled with new catalytic processes will provide the platform to produce green propene. We evaluate the technological and environmental merits of dehydrogenation catalysts. Currently, non-oxidative direct dehydrogenation (DDH) is the only commercialised process, and this is reflected in the high space-time yield commonly reported over the most active Pt or Cr catalysts. However, the formation of coke necessitates multi-reactor cycling to facilitate regeneration. Oxidative dehydrogenation using O2 (ODH-O2) does not suffer from coke formation, but can lead to overoxidation, limiting the yield of propene. While no commercial processes have yet been developed, a promising new class of active and selective ODH-O2 catalysts has emerged which use boron as the active component. The use of CO2 as a soft oxidant (ODH-CO2) has also gained interest due to the environmental advantages of utilising CO2. Although this is an attractive prospect, the propene yields with these catalysts are considerably less active then DDH and ODH-O2 catalysts. Despite significant advances in the past decade, current ODH-CO2 catalysts remain far from displaying the activity levels necessary to be considered for commercial application. The specific requirements of catalyst design for each sub-reaction are discussed and we identify that the balance of acid and base sites on the catalyst surface is of paramount importance. Future catalyst design in DDH and ODH-O2 should focus on improving selectivity to propene, while ODH-CO2 catalysts are limited by their low intrinsic activity. The scarcity of some common catalytic elements is also discussed, with recommendations focusing on more abundant chemical elements. Future research should focus on the low temperature activation of CO2 as a priority. With further research and development of lower energy routes to propene based on the dehydrogenation of sustainably-sourced propane, it should be possible to transform the manufacturing landscape of this key chemical intermediate

Lanthanum modified Fe-ZSM-5 zeolites for selective methane oxidation with H2O2

Selective partial oxidation of methane to methanol under ambient conditions is a great challenge in chemistry. Iron modified ZSM-5 catalysts are shown to be effective for this reaction using H2O2 as the oxidant. However, the high consumption of H2O2 over this catalyst presents a major disadvantage. Here we report a lanthanum modified Fe-ZSM-5 (LaFe-ZSM-5) catalyst for enhanced selective methane oxidation with suppressed H2O2 consumption. Using 0.5 wt% LaFe-ZSM-5 pretreated with H2 the productivity of primary oxygenated products (CH3OH, CH3OOH, HCOOH) is 3200 mol kgLaFe−1 h−1 in 0.1 M H2O2, with a selectivity of 98.9% to primary oxygenated products. The productivity is increased to 11 460 mol kgLaFe−1 h−1 in 0.5 M H2O2. Compared with Fe-ZSM-5, LaFe-ZSM-5 uses 31% less H2O2 for obtaining per mol of product under the same conditions. In situ DRIFT spectroscopy and solid state MAS NMR revealed the high H2O2 consumption in ZSM-5 based catalyst maybe closely related to the acidity of strong Brønsted acid sites (Si(OH)Al). The La modified ZSM-5 catalyst can decrease the acidity of the strong Brønsted acid sites and this suppresses the decomposition of H2O2

Selective oxidation of methane to methanol and methyl hydroperoxide over palladium modified MoO3 photocatalyst under ambient conditions

Selective partial oxidation of methane to valuable oxygenated products remains a great challenge, as typically over oxidation of oxygenated products to COx is observed. Weak oxidative species on the catalyst surface have a great potential to overcome this limitation. However, weak oxidative species usually have low concentrations and are easily decomposed. Here we report a Pd/MoO3 photocatalyst which can realize excellent methane oxidation to methanol and methyl hydroperoxide in pure water, under simulated solar light by in situ generated H2O2 at room temperature and pressure. The combined selectivity for methanol and methyl hydroperoxide is up to 98.6%, representing a productivity rate of 42.5 μmol gcat−1 h−1. Further studies on the reaction mechanism indicate that PdO species on the Pd loaded MoO3 catalyst play an essential role in the suppression of over oxidation. In this case PdO traps the photo-generated electrons, leaving photo-generated holes for decomposition of H2O2 into weak oxidative hydroperoxyl radicals which are not involved in the formation of over oxidation products

Designing novel amorphous catalysts for the propane dehydrogenation reaction

Global demand for propene, a major platform chemical with a myriad of uses in the manufacturing and chemical industry, is anticipated to continue to grow annually. The expected growth in propene demand cannot be met by existing processes, therefore direct or on-purpose processes are being developed to fill the so-called ‘propene gap’. Many of the technologies employed for the commercial dehydrogenation of propane operate using various Pt-based catalysts. This work addresses the rationale catalyst design of the support material and the supported metal catalyst with the aim of unlocking new catalyst design strategies. Hence, the investigations into catalyst design based on amorphous/disordered materials with an anticipated higher density of active sites for acid-catalysed catalytic reactions, are of great importance. This work addresses the systematic design of a new supercritical antisolvent-mediated (SAS) route to amorphous silica-alumina materials exploring the effect of solvent composition, process temperature, process pressure, calcination conditions, and choice of metal precursors. A route to a series of optimized and systematically varied amorphous silica-alumina was realised and the experimental approach was backed up by detailed advanced characterization. The synthesis strategy has not been previously reported in literature and preliminary investigations revealed bulk (microstructural) and local (nanoscale) structural similarities to analogous state-of-the-art, flame-spray pyrolysis (FSP) synthesized materials. Subsequent work focussed on finding and applying a reproducible method to deposit platinum nanoparticles with small particle size and size distribution onto the support. Catalytic evaluation was carried out on two acid-catalysed reactions, the propane dehydrogenation reaction and catalytic dehydration of methanol-to-DME (MTD). A combination of XRD, TGA, NH3-TPD, Pyridine-DRIFTS, (heteronuclear 1D MAS and 2D 27Al MQMAS) Solid-state NMR, XPS, SEM/EDX, FTIR/ATR, HRTEM, and SAED helped establish structure-performance relations. Through careful catalyst design, Pt/SAS-4 and Pt/FSP-4 catalysts with moderate surface acidity displayed the highest catalyst activity, productivity, and stability. The results found the catalyst performance to be comparable to and/or superior to analogous Pt-based catalysts supported on crystalline supports and reported in literature. Similar activity correlations were realised in the methanol-to-dimethyl ether reactions, and the key active component of the catalyst was surface acidity namely the nature, concentration, density, and balance of acid sites. A combination of several factors including aluminium speciation, morphology and surface acidity of the support explained the variations in catalytic activity. In the supported metal catalyst morphology and surface acidity played an active role in the redox properties of the support and its interaction with supported metal particles. The high propene yield, propene productivity and stability of Pt supported on supercritical antisolvent precipitation and flame spray pyrolysis synthesized SiO2-Al2O3 was attributed to a high proportion of coexistent AlIV - and AlV -based Brønsted acid sites within the support. The former was responsible for propane activation and the latter for anchoring and stabilising deposited nanoparticles; a key observation over a 16-hour non-oxidative propane dehydrogenation reaction. Therefore, the presence of a high proportion of AlV polyhedral, increased elemental homogeneity and high density of homotopic acid sites was used to rationalise a lot of the fundamental findings and relationships observed during this work. From the combined experimental, characterization and catalytic study, moderate aluminium content (Si/Al) and thus surface acidity was pertinent to enhanced catalyst activity, selectivity and stability in acid-catalysed reactions. The implications of this work in improving the understanding of novel, robust catalyst design and subsequent catalytic applications in the field of acid-catalyzed reactions has been explored

Ecological responses of periphyton dry mass and epilithic diatom community structure for different atrazine and temperature scenarios

Climate change–induced temperature increase may influence the ecotoxicity of agricultural herbicides such as atrazine and consequently negatively impact aquatic biota. The objective of this study was to assess the effects of increased temperature on the ecotoxicity of atrazine to diatom community structure and stream periphyton load using laboratory microcosm experiments. A natural periphyton community from the Mukwadzi River, Zimbabwe, was inoculated into nine experimental systems containing clean glass substrates for periphyton colonisation. Communities were exposed to 0 µg∙L-1 (control), 15 µg∙L-1 and 200 µg∙L-1 atrazine concentrations at 3 temperature levels of 26°C, 28°C and 30°C. Periphyton dry weight and community taxonomic composition were analysed on samples collected after 1, 2 and 3 weeks of colonisation. A linear mixed-effects model was used to analyse the main and interactive effects of atrazine and temperature on dry mass, species diversity, evenness and richness. Temperature and atrazine had significant additive effects on species diversity, richness and dry mass. As temperature increased, diatom species composition shifted from heat-sensitive species such as Achnanthidium affine to heat-tolerant species such as Achnanthidium exiguum and Epithemia adnata. Increasing temperature in aquatic environments contaminated with atrazine results in sensitive and temperature-intolerant diatoms being eliminated from periphyton communities. Climate change will exacerbate effects of atrazine on periphyton dry mass and diatom community structure

Conversion of levulinic acid to levulinate ester biofuels by heterogeneous catalysts in the presence of acetals and ketals

The esterification of levulinic acid under acidic conditions to produce levulinate esters is of current significant interest due to the potential of these compounds as fuels and fuel additives. While a number of bespoke heterogeneous catalysts have been reported to be effective for this transformation, the use of widely available commercial catalysts has generally proved to be ineffective, with only low conversions to ester products being achieved. Herein, we report a novel strategy for the efficient synthesis of levulinate esters from levulinic acid in the presence of trialkyl orthoformates or dialkyl acetals and ketals catalyzed by commercial catalysts, such as ZSM-5 and Amberlyst-15. These reactions proceed under mild conditions and in short reaction times to selectively produce high yields of levulinate esters