Ethylene dimerization is an efficient industrial chemical process to produce 1‐butene, with demanding selectivity and activity requirements on new catalytic systems. Herein, a series of monodentate phosphinoamine‐nickel complexes immobilized on UiO‐66 are described for ethylene dimerization. These catalysts display extensive molecular tunability of the ligand similar to organometallic catalysis, while maintaining the high stability attributed to the metal–organic framework (MOF) scaffold. The highly flexible postsynthetic modification method enables this study to prepare MOFs functionalized with five different substituted phosphines and 3 N‐containing ligands and identify the optimal catalyst UiO‐66‐L5‐NiCl2 with isopropyl substituted nickel mono‐phosphinoamine complex. This catalyst shows a remarkable activity and selectivity with a TOF of 29 000 (molethyl/molNi/h) and 99% selectivity for 1‐butene under ethylene pressure of 15 bar. The catalyst is also applicable for continuous production in the packed column micro‐reactor with a TON of 72 000 (molethyl/molNi). The mechanistic insight for the ethylene oligomerization has been examined by density functional theory (DFT) calculations. The calculated energy profiles for homogeneous complexes and truncated MOF models reveal varying rate‐determining step as β‐hydrogen elimination and migratory insertion, respectively. The activation barrier of UiO‐66‐L5‐NiCl2 is lower than other systems, possibly due to the restriction effect caused by clusters and ligands. A comprehensive analysis of the structural parameters of catalysts shows that the cone angle as steric descriptor and butene desorption energy as thermodynamic descriptor can be applied to estimate the reactivity turnover frequency (TOF) with the optimum for UiO‐66‐L5‐NiCl2. This work represents the systematic optimization of ligand effect through combination of experimental and theoretical data and presents a proof‐of‐concept for ethylene dimerization catalyst through simple heterogenization of organometallic catalyst on MOF.

Sluggish kinetics of the anodic oxygen evolution reaction (OER) and minor upstream upsets in feed water quality remain bottlenecks for efficient water electrolysis, which is exacerbated under near-neutral pH environments due to H2O dissociation. In this work, we report the introduction of a NiSx interlayer in a Co-(NiFe) oxide/nitride catalyst on nickel foam substrate. Postmortem OER characterization in neutral pH synthetic seawater (SSW) shows that stable cationic [Co-(NiFe)]& delta;+ and anionic [O-N]& delta;- surface species coupled with the NiSx interlayer accelerate H2O dissociation, thereby enhancing activity and kinetics. The electrocatalysts exhibit stable performance at 100 mA cm-2 for 50 h in alkaline and neutral pH SSW with 350 and 425 mV of overpotential, respectively. The faradaic efficiency of the NiSx interlayer catalysts is enhanced by 10.3% and 8.5% achieving 94.5% and 87.4% under alkaline and neutral pH SSW, respectively, during chronoamperometry tests at a high applied voltage of 1.75 V (vs. RHE).

To explore options for simple, safe, and compact chemical reactors that preserve wanted metastable initial products from sequential unwanted reactions, academic and industrial researchers have tried to repurpose reciprocating piston equipment or an "engine-like" design to be used as a chemical reactor. Piston reactors offer the benefit of achieving very high temperature and pressure conditions at very short and defined residence times. Such conditions offer promise for enhanced performance for several chemical conversions. This paper provides a review of the published literature and patents in the field of piston reactors to provide an overview of the current state-of-the-art. The review covers multiple aspects of piston reactors and their applications, reactor design options and their operation, catalyst and ignition placement, tested reactions, experimental setups as well as modeling and simulation. Several research gaps are highlighted as a motivation for future research in the field. To help interested readers into the topic, basic concepts and fundamentals of piston reactors are provided.

This study deals with the development and evaluation of lanthana promoted Cu-based catalysts for CO2 hy-drogenation reaction. The samples were prepared using solution combustion synthesis method. The study demonstrates that the incorporation of 3wt% lanthana (La2O3) into a CuO/ZnO/Al2O3 results in a catalyst with exceptionally high catalytic performance. The synthesized catalysts were thoroughly characterized by various analytical tools such as HRTEM, XRD, XPS, H2-TPR, H2-TPD and CO2-TPD. The catalysts were assessed for CO2 hydrogenation reaction in a high-pressure fixed-bed reactor. The La2O3 promoted catalyst with a composition of 0.6Cu/0.3ZnO/0.03La2O3/0.07Al2O3 was selective to methanol (60%) even at an operating temperature as high as 325 degrees C and an operating pressure of 85 bars. Under similar operating conditions, the 0.6Cu/0.3ZnO/ 0.03La2O3/0.07Al2O3 catalyst exhibited better CO2 conversion, MeOH selectivity and MeOH production as compared to unpromoted catalyst, 0.6Cu/0.3ZnO/0.1Al2O3. At reaction conditions of T = 300 degrees C, P = 85 bar, and GHSV=55,000h-1, the lanthana promoted catalyst showed a CO2 conversion and methanol selectivity of 20% and 65%, respectively; while the production rates of carbon monoxide and methanol were 0.55 g/g-cat h-1 and 0.79 g/g-cat h-1. The high catalytic efficiency is attributed to the formation of oxygen vacancies and/or generation of defects in the catalyst surface, smaller Cu nanoparticles with LaOx, and a comparable larger number of mild basic sites. Similar catalyst prepared by wet impregnation method performed poorly, thus highlighting the role of combustion synthesis and the effect of temperature in forming unique metal oxide phases responsible for higher catalytic performance.

Green hydrogen presents itself as a clean energy vector, which can be produced by electrolysis of water by utilizing renewable energy such as solar or wind. While current technologies are sufficient to support commercial deployment of fresh water electrolyzers, there remain a few well-defined challenges in the path of commercializing direct seawater electrolyzers, predominantly related to the sluggish oxygen evolution reaction (OER) kinetics and the competing chlorine evolution reaction (CER) at the anode. Herein, we report the facile and swift fabrication of an S,B-codoped CoFe oxyhydroxide via solution combustion synthesis for the OER with apparent CER suppression abilities. The as-prepared S,B-(CoFe)OOH-H attained ultralow overpotentials of 161 and 278 mV for achieving current densities of 10 and 1000 mA cm-2, respectively, in an alkaline saline (1 M KOH + 0.5 M NaCl) electrolyte, with a low Tafel slope of 46.7 mV dec-1. Chronoamperometry testing of the codoped bimetallic oxyhydroxides showed very stable behavior in harsh alkaline saline and in neutral pH saline environments. S,B-(CoFe)OOH-H oxyhydroxide showed a notable decrease in CER production in comparison to the other S,B-codoped counterparts. Selectivity measurements through online FE calculations showed high OER selectivity in alkaline (FE ∼ 97%) and neutral (FE ∼ 91%) pH saline conditions under standard 10 mA cm-2 operation. Moreover, systematic testing in electrolytes at pH values of 14 to 7 yielded promising results, thus bringing direct seawater electrolysis at near-neutral pH conditions closer to realization.

This work investigates the effects of solution combustion synthesis (SCS) variables on the performance of copper-based catalysts for CO2 hydrogenation to methanol. The catalyst with a composition of 30wt%CuO50%ZnO/Al2O3 was prepared at various glycine to nitrates (G/O) ratios in the range between 0.1 and 1.23. A correlation of the effects of calcination and activation temperatures with catalytic activity was also studied. The catalyst synthesized at a G/O ratio of 0.206, calcined in air at 400 °C and activated in a stream of pure hydrogen at a temperature of 350 °C resulted in a significant improvement in the performance of the catalyst for CO2 hydrogenation. The exceptionally high catalytic performance of the catalyst was attributed to the synergic effects between small well-dispersed CuO nanoparticles and high number of induced copper phases. The highest activity of the catalyst was recorded at an operating temperature of 300 °C, a pressure of 85 bar and GHSV of 7000 h−1. The CO2 conversion, CO selectivity and methanol selectivity under these conditions were 30%, 38.60%, and 61.4%, respectively; whereas, methanol and CO yields were 0.52gMeOH/g-cat.h and 0.33gCO/g-cat.h, respectively.

In this work, we demonstrate a simple sol-gel technique to prepare metal-ion(s)-doped ceria-zirconia solid solution for efficient catalytic methane activation. The cation-depicting formula units are Ce0.80Zr0.20 (CZ), Ce0.79Zr0.20M0.01 (CZM), and Ce0.79Zr0.20M0.005M10.005 (CZMM1) (M and M1 = V, Mn, Fe, Co, and Cu), employed for undoped, mono-metal-ion-doped, and bi-metal-ion-doped solid solutions, respectively. Methane activation with Mn, Fe, Cu mono-metal-ion-doped CZ favors the C1 product, while CZCo assists C-C coupling with the formation of acetaldehyde. On the other hand, the Co- and Fe-doped bi-metal-ion combination catalyst (CZCoFe) shows significant ethanol but predominant formic acid formation. This is further promoted by the Co + V bi-metal-ion combination (CZCoV) catalyst, and it shows ethanol as the major product along with methyl hydrogen peroxide, methanol, and formic acid as minor products. An impressive ethanol yield of 93 μmol/g h with 76% selectivity obtained with the CZCoV catalyst is at par with that obtained with noble-metal-based catalysts under comparable reaction conditions. When Co and V content was increased two and four times from 0.005 to 0.01 and 0.02, ethanol yield increased at the expense of formic acid. The 213 μmol/g h ethanol yield (86% selectivity) observed with Ce0.76Zr0.20Co0.02V0.02 is probably the highest observed. The partial oxidation of CH4 in Co-based bi-metal combinations (Co + V or Co + Fe) suggests the synergistic effect of doped metal ions owing to the heterogeneous near-neighbor environment. The present results are attributed to the surface heterogeneity between the host and the dopants, which selectively promotes methane activation as well as C-C coupling. This indicates a large scope to tune the activity of partial oxidation of methane and product selectivity with different metal-ion(s) combinations.

CO2 capture and conversion to value-added products have seen continued advancement in recent years through electrochemical and thermochemical routes. In this work, we have adapted a facile and potentially scalable thermochemical reduction technique that directly reduces CO2 to different-quality reduced graphene oxide (rGO) solids. Several characterization techniques have been undertaken to investigate the role of two- and three-dimensional copper catalytic substrates, reaction time, and CO2 humidity content on the characteristics of the prepared rGO. Growth for 1 h at 550 degrees C atop a uniform two-dimensional (2D) catalytic copper substrate under a humidified CO2 environment (0.14 g(H2O)/g(CO2)) attained rGO with low defect densities (0.36 x 10(11) cm(-2)) and high domain (31.9 nm) and crystallite (3.32 nm) sizes. Detailed statistical Raman analyses over large areas confirm that the mean defect distance of the synthesized rGO samples is 16-20 nm, indicative of the intrinsic high quality attained. The degree of reduction in rGO based on C/O ratios from 4 to 8 suggests that operating conditions can be fine-tuned to attain different-quality rGO with different attributable macroproperties such as conductivity and hydrophilicity. The developed method of direct CO2 reduction to rGO can be further tuned to produce different quality, morphology, and yield of other high-value solid carbon-based materials for emerging and existing applications.

Using abundant seawater can reduce reliance on freshwater resources for hydrogen production from electrocatalytic water splitting. However, seawater has detrimental effects on the stability and activity of the hydrogen evolution reaction (HER) electrocatalysts under different pH conditions. In this work, we report the synthesis of binary metallic core-sheath nitride@oxynitride electrocatalysts [Ni(ETM)]δ+-[O-N]δ-, where ETM is an early transition metal V or Cr. Using NiVN on a nickel foam (NF) substrate, we demonstrate an HER overpotential as low as 32 mV at -10 mA cm-2 in saline water (0.6 M NaCl). The results represent an advancement in saline water HER performance of earth-abundant electrocatalysts, especially under near-neutral pH range (i.e., pH 6-8). Doping ETMs in nickel oxynitrides accelerates the typically rate-determining H2O dissociation step for HER and suppresses chloride deactivation of the catalyst in neutral-pH saline water. Heterointerface synergism occurs through H2O adsorption and dissociation at interfacial oxide character, while adsorbed H* proceeds via Heyrovsky or Tafel step on the nitride character. This electrocatalyst showed stable performance under a constant current density of -50 mA cm-2 for 50 h followed by additional 50 h at -100 mA cm-2 in a neutral saline electrolyte (1 M PB + 0.6 M NaCl). Contrarily, under the same conditions, Pt/C@NF exhibited significantly low performance after a mere 4 h at -50 mA cm-2. The low Tafel slope of 25 mV dec-1 indicated that the reaction is Tafel limited, unlike commercial Pt/C, which is Heyrovsky limited. We close by discussing general principles concerning surface charge delocalization for the design of HER electrocatalysts in pH saline environments.

Application of noble metal-free electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) during electrocatalytic water splitting is crucial for clean energy conversion and has drawn extensive attention. However, the development of highly active and low cost electrocatalysts is a considerable challenge. Herein, Co-Cu alloy nanoparticles-incorporated carbon nanowires electrocatalyst was synthesized and evaluated for both OER and HER. The nanomaterials were fabricated by facile electrospinning of sol-gel composed of cobalt acetate, copper acetate, and poly(vinyl alcohol) followed by calcination in an inert environment. Adjusting the composition of the metallic counterpart was found to significantly enhance electrochemical properties of the catalyst. Furthermore, the unique nanowire morphology and structural properties of incorporated Co-Cu alloy, the (Co0.95Cu0.05@CHWs) composition exhibits good electrocatalytic performance for both OER and HER in the alkaline medium. Physicochemical characterizations using X-ray diffraction, X-ray photoelectron spectroscope, scanning electron microscopy, and transmission electron microscopy have confirmed the formation of alloy structure and nanowire morphology. The optimum composition (Co0.05Cu0.05@CNWs) requires small overpotential, eta(10) of similar to 285 mV for oxygen evolution reaction (OER) and similar to 160 mV for hydrogen evolution reaction (HER) with the corresponding Tafel slope of 92 mV dec 1 and 172 mV dec(-1) versus the reversible hydrogen electrode, respectively. In addition, only negligible loss in activity was observed after 1000 cycles and prodeces cell voltage of 1.58 Vat current of 10 mA/cm(2) and 1.72 Vat current density of 50 mA/cm(-1) in two electrode system. Density Functional Theory (DFT) calculations were employed to verify experimental results. Electronic density of states (DOS) results reveal an increase in electronic states near the Fermi level upon Co-Cu heterojunctioning with CNW5. This is indicative of improved catalytic activity and more favorable binding energies of HER and OER intermediates. Reaction coordinate diagrams for HER and OER were developed, which aided in identifying thermodynamically limiting steps. This work may provide a feasible approach for incorporating other transition metals to design low-cost and high-performance bifunctional electrocatalysts for overall water splitting. (C) 2021 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Catalytic methane decomposition (CMD) is a highly promising approach for the rational production of relatively COx-free hydrogen and carbon nanostructures, which are both important in multidisciplinary catalytic applications, electronics, fuel cells, etc. Research on CMD has been expanding in recent years with more than 2000 studies in the last five years alone. It is therefore a daunting task to provide a timely update on recent advances in the CMD process, related catalysis, kinetics, and reaction products. This mini-review emphasizes recent studies on the CMD process investigating self-standing/supported metal-based catalysts (e.g., Fe, Ni, Co, and Cu), metal oxide supports (e.g., SiO2, Al2O3, and TiO2), and carbon-based catalysts (e.g., carbon blacks, carbon nanotubes, and activated carbons) alongside their parameters supported with various examples, schematics, and comparison tables. In addition, the review examines the effect of a catalyst's shape and composition on CMD activity, stability, and products. It also attempts to bridge the gap between research and practical utilization of the CMD process and its future prospects.

Vanadium-doped acid prepared mesoporous spheres (V-APMS) were prepared with vanadium loadings of 1–40wt% using a wet-impregnation method. The effects of vanadium loading on the support were studied using N2 physisorption and powder XRD. The pore volumes, surface areas, and pore diameters of the catalysts decreased as a function of vanadium loading and diffraction peaks corresponding to crystalline V2O5 were detected by XRD at an intermediate V loading, becoming more intense as the V content increased. These results indicate that at low V loadings, the vanadium oxide species were well-dispersed on the silica; however, at higher V loadings crystalline V2O5 was formed within the pores of the APMS. V-APMS was then studied as a heterogeneous catalyst for the oxidation of the chemical warfare agent stimulant 2-chloroethyl ethyl sulfide (CEES) using tert-butyl hydroperoxide (TBHP) as the oxidant. Kinetic studies at temperatures ranging from 0 to 50°C showed that materials with low V loadings were the most effective catalysts for the reaction. The mechanism of the oxidation reaction appeared to be different for catalysts that were composed of well-dispersed vanadium oxide species than for catalysts containing microcrystalline or crystalline V2O5. Finally, a possible reaction scheme for the oxidation of CEES by V-APMS is discussed.

This paper presents a study on the synthesis of Ti-MMM-2 (Ti-MCM-48/TS-1) mixed-phase materials prepared by a one-pot method using different gemini surfactants and TPA(+) ions. Powder XRD and Si-29 MAS-NMR reveal that materials prepared using longer chain gemini surfactants such as 22-12-22 favored the formation of TS-1 more strongly than the shorter 16-12-16 surfactant. N-2 physisorption data shows a decrease in surface area and pore volume and an increase in pore diameter as the surfactant chain length is increased.

This paper presents studies on the immobilization of the polyoxometalate [PV2Mo10O40]−5 (referred to as “POM”) on modified mesoporous MCM-41. The MCM-41 host material was made cationic by functionalization of the surface with [(MeO)3Si(CH2)3N+(CH3)3]Cl. In polar solvents, POM is deprotonated and could be easily immobilized by wet impregnation of the modified silica using MeOH as the solvent. The physical properties of the samples were examined using XRD, FTIR, DR UV–Vis spectroscopy, 31P MAS-NMR, N2 physisorption, and TEM. These techniques indicated that the POM is intact on the surface after impregnation. High loadings of POM caused a decrease in the surface area and pore volume of the solid, presumably due to both pore blockage and restructuring of the silica during wet impregnation. The texture and structure of the MCM-41 was studied as a function of POM loading.

The technique of small angle X-ray scattering (SAXS) has been employed to monitor the influence of uranium substitution on the pore characteristics of MCM-48 silica mesoporous material. The incorporation of uranium, as uranyl ion, at the framework silica sites resulted in the progressive increase in average pore size, the extent of which depended upon uranium loading. These results are in agreement with powder XRD results, showing a progressive increase in unit cell constant (a0) with increasing U-loading. The changes in the pore structure and the unit cell parameter are attributed to the perturbations arising due to bonding of (OUO)2+ units to Si–O− units, thus forming a local uranate type structure. However, the increase in uranium content beyond 3wt.% resulted in partial precipitation of uranium oxide crystallites, thus causing blocking/narrowing of some of the pores in the host material. SAXS results reveal that, in spite of these structural changes, the fractal nature of the host material remained by-and-large unchanged. These findings are in harmony with the results of the parallel studies conducted using N2-adsorption and TEM studies.

Quasielastic neutron scattering (QENS) and Fourier transform infrared spectroscopic studies were carried out on methanol molecules adsorbed in HMCM-41 and HZSM-5 molecular sieves to monitor the effect of pore structure on their occluded state under the conditions of ambient temperature and 5-250 mbar pressures. The QENS results have shown that the pore geometry of the host matrix and the dipolar character of the adsorbate are together responsible for the binding state of guest molecules in the confining medium. Thus, neither translational nor free rotational motion was noticed for methanol molecules adsorbed in HZSM-5, in contrast to benzene and cyclohexane molecules of almost similar size that are reported to undergo a rotational motion under the identical conditions of loading (Phys. Chem. Chem. Phys. 2001, 3, 4449; 2003, 5, 3066). In the case of HMCM-41, a translational motion of occluded methanol molecules was clearly observed with a diffusion constant D approximately 1.5 x 10(-5) cm2 s(-1), as compared to a value of D approximately 2.6 x 10(-5) cm2 s(-1) for its liquid state. These results indicate that the adsorbed methanol experiences a considerable extent of supercooling due to capillary condensation in zeolitic pores, giving rise to formation of a metastable state even at room temperature. In HZSM-5, entrapped methanol exists in an almost solidlike state, whereas in HMCM-41, its density lies between that of the solid and the liquid phases. Infrared spectroscopic study conducted using deuterium-labeled adsorbate and host matrixes have given evidence for different kinds of interactions between the methanol molecules and the host matrix, depending upon the loading. For small loadings the internal hydroxy groups within the pore system get perturbed first, giving rise to formation of the methoxy groups. Multilayer adsorption and capillary condensation of methanol occur for a loading of 0.05 mmol per gram and above, within the pore system and also at the external surface, giving rise to a highly compressed state due to strong intermolecular bonding. At the same time, a considerable amount of exchange occurred between the hydroxy groups of the adsorbed methanol and those of the host matrix. Such exchange of hydroxy groups may play an important role in the catalytic properties of the porous aluminosilicates.

The room temperature, liquid-phase oxidation of 2-chloroethyl ethyl sulfide (CEES), an analogue of mustard gas, was investigated using vanadium-doped acid-prepared mesoporous silica (“V−APMS”) as a solid catalyst. The V−APMS samples were prepared by wet impregnation with NH4VO3, followed by calcination. XRD, N2 physisorption, SEM, and EPR were used to characterize the solid products. Samples with lower V contents (0.1−10 wt %) were found to contain isolated vanadyl species and were highly effective for oxidation of CEES to the corresponding sulfoxide and sulfone using tert-butyl hydroperoxide (TBHP) as the oxidant. Surface area and pore volume decreased significantly at higher loadings of V due to formation of V2O5 within the pores of the solid. The mechanistic route involved V5+/V4+ redox cycles during the catalysis process, as revealed by EPR studies.