Reactions, Volume 2, Issue 3 (September 2021) – 10 articles

The goal of finding efficient and safe hydrogen storage material motivated researchers to develop several materials to fulfil the demand of the U.S. Department of Energy (DOE). In the past few years, several metal hydrides, complex hydrides such as borohydrides and alanates, have been researched and found efficient due to their high gravimetric and volumetric density. However, the development of these materials is still limited by their high thermodynamic stability and sluggish kinetics. One of the methods to improve the kinetics is to use catalysts. Among the known catalysts for this purpose, transition metals and their compounds are known as the leading contender. The present article reviews the d-block transition metals including Ni, Co, V, Ti, Fe and Nb as catalysts to boost up the kinetics of several hydride systems. Various binary and ternary metal oxides, halides and their combinations, porous structured hybrid designs and metal-based Mxenes have been discussed as catalysts to enhance the de/rehydrogenation kinetics and cycling performance of hydrogen storage systems. Full article

In this study, new mono- and di-alkoxido zirconium(IV) complexes supported by tetradentate dianionic cyclam ligands were synthesized and characterized. These compounds were obtained by reaction of the parent Zr(IV) dichlorido species with one or two equivalents of the corresponding lithium alkoxido, whereas (^3,5-Me2Bn₂Cyclam)Zr(OPh)₂ was prepared by protonolysis of the orthometallated species (3,5-Me-C₆H₄CH₂)₂Cyclam)Zr with phenol. The solid-state molecular structures of (Bn₂Cyclam)ZrCl(O^tBu) and (^4-tBuBn₂Cyclam)Zr(OⁱPr)₂ show a trigonal prismatic geometry around the metal centers. (Bn₂Cyclam)Zr(SPh)(O^tBu) and (Bn₂Cyclam)ZrMe(OⁱPr) were prepared by reaction of (Bn₂Cyclam)ZrCl(OR) (R = ⁱPr, ^tBu) with one equivalent of LiSPh or MeMgCl, respectively. The reactions of (Bn₂Cyclam)Zr(OⁱPr)₂ and (^4-tBuBn₂Cyclam)Zr(OⁱPr)₂ with carbon dioxide suggested the formation of species that correspond to the addition of four CO₂ molecules. Full article

The fate of dense non-aqueous phase liquids (DNAPLs) in the environment and the consequential remediation problems have been intensively studied over the last 50 years. However, a scarce literature is present about the mass transfer at the DNAPL/water interface. In this paper, we present a fast method for the evaluation of the mass transfer performance of a surfactant that can easily be employed to support an effective choice for the so-called enhanced remediation strategies. We developed a lab-scale experimental system modelled by means of simple ordinary differential equations to calculate the mass transfer coefficient (K) of trichloroethylene, chosen as representative DNAPL, in the presence and in the absence of two ethoxylated alcohols belonging to the general class of Synperonic surfactants. Our findings revealed that it exists an optimal surfactant concentration range, where K increases up to 40% with respect to pure water. Full article

The origin of an upper limit to the amount of O₂ evolved in the rapid reaction between Fe²⁺ and H₂O₂ was investigated at a high concentration of H₂O₂. Using a nonradical model, including the formation of a primary Fe²⁺–biperoxy complex with a diminished rate of formation of the active intermediate FeO²⁺, agreement has been reached for the first time with the experimental data obtained by Barb et al. A limited formation of O₂ requires that a finite concentration of H₂O₂ should be present in the reaction mixture when [Fe²⁺] falls to zero. It has been shown that in Barb et al.’s model the condition for such a state ([Fe²⁺] = 0, [H₂O₂] > 0) does not exist. Free radical based models fail as mechanisms for the Fenton reaction. Full article

The hydrogen storage properties of a multi-component alloy of composition Ti_0.3V_0.3Mn_0.2Fe_0.1Ni_0.1 were investigated. The alloy was synthesized by arc melting and mechanical alloying, resulting in different microstructures. It was found that the as-cast alloy is multiphase, with a main C14 Laves phase matrix along with a BCC phase and a small amount of Ti₂Fe-type phase. The maximum hydrogen storage capacity of the alloy was 1.6 wt.%. We found that the air-exposed samples had the same capacity as the as-cast sample but with a longer incubation time. Synthesis by mechanical alloying for five hours resulted in an alloy with only BCC structure. The hydrogen capacity of the milled alloy was 1.2 wt.%, lower than the as-cast one. The effect of ball milling of the as-cast alloy was also studied. Ball milling for five hours produced a BCC structure similar to the one obtained by milling the raw materials for the same time. Full article

Highly dispersed Mn metallic nanoparticles (15.87 nm on average) on a nitrogen-doped porous carbon matrix were prepared by thermal treatment of MnO_2-x/polyaniline (PANI), which was derived from the in situ polymerization of aniline monomers initiated by γ-MnO₂ nanosheets. Owing to the large surface area (1287 m²/g), abundant active sites, nitrogen dopants and highly dispersed Mn sites on graphitic carbon, an impressive specific capacity of 1319.4 mAh g⁻¹ with an admirable rate performance was delivered in a Li-S battery. After 220 cycles at 1 C, 80.6% of the original capacity was retained, exhibiting a good cycling stability. Full article

We investigated the effect of pre-treatment conditions on the activity and selectivity of cobalt catalysts for Fischer–Tropsch synthesis (FTS) by varying both the reduction atmosphere and the reduction temperature. Catalysts supported on SiO₂, Al₂O₃, and TiO₂, prepared via incipient wetness impregnation, were evaluated, and activation temperatures in the range 250–350 °C were considered. Activation with syngas led to a better product selectivity (low CH₄, high selectivity to liquid hydrocarbons, and low paraffin to olefin ratio (P/O)) than the catalysts reduced in H₂ at lower activation temperatures. The Co_xC species suppressed the hydrogenation reaction, and it is hypothesised that this resulted in the high selectivity of olefins observed for the syngas pre-treated catalysts. On the basis of the experimental results, we postulated that a synergistic effect between Co⁰ and Co_xC promotes the production of the long chain hydrocarbons and suppresses the formation of CH₄. In addition, for systems aimed at producing lower olefins, syngas activation is recommended, and for the FTS plants that focus on maximising the production of higher molecular weight products, H₂ activation might be considered. These results provide insights for the future FTS catalyst design and for target product-driven operations. Full article

Light olefins as one the most important building blocks in chemical industry can be produced via Fischer–Tropsch synthesis (FTS) from syngas. FT synthesis conducted at high temperature would lead to light paraffins, carbon dioxide, methane, and C₅₊ longer chain hydrocarbons. The present work focuses on providing a critical review on the light olefin production using Fischer–Tropsch synthesis. The effects of metals, promoters and supports as the most influential parameters on the catalytic performance of catalysts are discussed meticulously. Fe and Co as the main active metals in FT catalysts are investigated in terms of pore size, crystal size, and crystal phase for obtaining desirable light olefin selectivity. Larger pore size of Fe-based catalysts is suggested to increase olefin selectivity via suppressing 1-olefin readsorption and secondary reactions. Iron carbide as the most probable phase of Fe-based catalysts is proposed for light olefin generation via FTS. Smaller crystal size of Co active metal leads to higher olefin selectivity. Hexagonal close-packed (HCP) structure of Co has higher FTS activity than face-centered cubic (FCC) structure. Transition from Co to Co₃C is mainly proposed for formation of light olefins over Co-based catalysts. Moreover, various catalysts’ deactivation routes are reviewed. Additionally, techno-economic assessment of FTS plants in terms of different costs including capital expenditure and minimum fuel selling price are presented based on the most recent literature. Finally, the potential for global environmental impacts associated with FTS plants including atmospheric and toxicological impacts is considered via lifecycle assessment (LCA). Full article

The experimental data on hydrogen adsorption on five nanoporous activated carbons (ACs) of various origins measured over the temperature range of 303–363 K and pressures up to 20 MPa were compared with the predictions of hydrogen density in the slit-like pores of model carbon structures calculated by the Dubinin theory of volume filling of micropores. The highest amount of adsorbed hydrogen was found for the AC sample (ACS) prepared from a polymer mixture by KOH thermochemical activation, characterized by a biporous structure: 11.0 mmol/g at 16 MPa and 303 K. The greatest volumetric capacity over the entire range of temperature and pressure was demonstrated by the densest carbon adsorbent prepared from silicon carbide. The calculations of hydrogen density in the slit-like model pores revealed that the optimal hydrogen storage depended on the pore size, temperature, and pressure. The hydrogen adsorption capacity of the model structures exceeded the US Department of Energy (DOE) target value of 6.5 wt.% starting from 200 K and 20 MPa, whereas the most efficient carbon adsorbent ACS could achieve 7.5 wt.% only at extremely low temperatures. The initial differential molar isosteric heats of hydrogen adsorption in the studied activated carbons were in the range of 2.8–14 kJ/mol and varied during adsorption in a manner specific for each adsorbent. Full article

The benzo[1,2,3]dithiazole is a unique heteroaromatic functionality whose conjugated profile instils some fascinating electronic properties. This has been historically recognized in the design and manufacture of organic dyes early last century. Although, with the benefit of increased diagnostic techniques and improved understanding, these structures are attracting greater attention in additional research settings, including applications as organic radicals and semiconductors. In addition, the benzodithiazole functionality has been shown to be a valuable synthetic intermediate in the preparation of a variety of other privileged aromatic and heteroaromatic targets, many of which are important APIs. In this review, the authors aim to critically analyse the potential applicability of these compounds to the fields of not only small-scale laboratory synthetic and medicinal chemistry but also commercial-scale processes and increasingly materials chemistry. Full article