Activation of Cobalt Foil Catalysts for CO Hydrogenation

CO hydrogenation has been studied on cobalt foils as model catalysts for Fischer–Tropsch (FT) synthesis. The effect of pretreatment (number of calcinations and different reduction times) for cobalt foil catalysts at 220 °C, 1 bar, and H2/CO = 3 has been studied in a microreactor. The foils were examined by scanning electron microscopy (SEM). It was found that the catalytic activity of the cobalt foil increases with the number of pretreatments. The mechanism is likely an increase in the available cobalt surface area from progressively deeper oxidation of the foil, supported by surface roughness detected by SEM. The highest FT activity was obtained using a reduction time of only 5 min (compared to 1 and 30 min). Prolonged reduction caused the sintering of cobalt crystallites, while too short of a reduction time led to incomplete reduction and small crystallites susceptible to low turn-over frequency from structure sensitivity. Larger crystals from longer reduction times gave increased selectivity to heavier components. The paraffin/olefin ratio increased with the increasing number of pretreatments due to olefin hydrogenation favored by enhanced cobalt site density. From the results, it is suggested that olefin hydrogenation is not structure sensitive, and that mass transfer limitations may occur depending on the pretreatment procedure. Produced water did not influence the results for the low conversions experienced in the present study (<6%).

The Effect of Dicarboxylic Acid Catalyst Structure on Hydrolysis of Cellulose Model Compound D-Cellobiose in Water

Background: Polycarboxylic acids are of interest as simple mimics for cellulase enzyme catalyzed depolymerization of cellulose. In this study, DFT calculations were used to investigate the effect of structure on dicarboxylic acid organo-catalyzed hydrolysis of cellulose model compound D-cellobiose to D-glucose. Methods: Binding energy of the complex formed between D-cellobiose and acid (Ebind), as well as glycosidic oxygen to dicarboxylic acid closest acidic H distance were studied as key parameters affecting the turn over frequency of hydrolysis in water. Result: α-D-cellobiose - dicarboxylic acid catalyst down face approach showed high Ebind values for five of the six acids studied; indicating the favorability of down face approach. Maleic, cis-1,2-cyclohexane dicarboxylic, and phthalic acids with the highest catalytic activities showed glycosidic oxygen to dicarboxylic acid acidic H distances 3.5-3.6 Å in the preferred configuration. Conclusion: The high catalytic activities of these acids may be due to the rigid structure, where acid groups are held in a fixed geometry.

Natural mineral modulated single atom catalyst for effective water treatment

Single atom catalysts (SACs) have been growing as an emerging “hot” topic in environmental remediation. Their performance can be rationally optimized via modulating spatial coordination configuration and porous structure of SACs, which is still challenging. Herein, a novel Si, N co-coordinated cobalt SACs (p-CoSi1N3@D) with 3D freestanding architecture was tailored via employing natural mineral (diatomite) as Si source and porous template. Theoretical calculations and experimental analysis reveal that Si substitution dramatically decreases electronegativity of CoN4 moieties and thus accelerates interaction and electron transfer between peroxymonosulfate and Co single atom center. Moreover, p-CoSi1N3@D inherits hierarchically porous architecture of diatomite, providing more accessible cobalt sites and open diffusion channels for peroxymonosulfate and contaminants in water treatment applications. Thanks to optimal coordination structure and porous architecture, p-CoSi1N3@D can serve as highly active catalyst toward peroxymonosulfate activation, with a turn-over frequency of 299.8 min− 1 for bisphenol A degradation, surpassing those of catalysts with transition metal SACs or oxides in disclosed literature. This work provides a novel vision for development of SACs towards wastewater reclamation.

Anchoring Copper Single Atoms on Porous Boron Nitride Nanofiber to Boost Selective Reduction of Nitroaromatics

Single atom catalysts have received widespread attention for their fascinating performance in terms of metal atom efficiency as well as their unique catalysis mechanisms comparing to conventional catalysts. Here, we prepared a high-performance catalyst of single-Cu-atom-decorated boron nitride nanofibers (BNNF-Cu) via a facile calcination method for the first time. The as-prepared catalyst shows excellent catalytic activity and good stability for converting different nitro compounds into their corresponding amines both with and without photoexcitation. By combined studies using synchrotron radiation analysis, high-resolution high-angle annular dark-field transmission electron microscopy studies and DFT calculation, dispersion and coordination of Cu atoms as well as their catalytic mechanisms are explored. The BNNF-Cu catalyst is found to have a record high turn-over frequency comparing to previously reported nonprecious-metal-based catalysts. While the performance of the BNNF-Cu catalyst is only of the middle range level among the state-of-the-art precious-metal-based catalysts, due to the much lower cost of the BNNF-Cu catalyst, its cost-efficiency is the highest among these catalysts. This work provides a new choice of support material which can promote the development of single atoms catalysts.

A Molecular Tetrahedral Cobalt–Seleno-Based Complex as an Efficient Electrocatalyst for Water Splitting

The cobalt–seleno-based coordination complex, [Co{(SePiPr2)2N}2], is reported with respect to its catalytic activity in oxygen evolution and hydrogen evolution reactions (OER and HER, respectively) in alkaline solutions. An overpotential of 320 and 630 mV was required to achieve 10 mA cm−2 for OER and HER, respectively. The overpotential for OER of this CoSe4-containing complex is one of the lowest that has been observed until now for molecular cobalt(II) systems, under the reported conditions. In addition, this cobalt–seleno-based complex exhibits a high mass activity (14.15 A g−1) and a much higher turn-over frequency (TOF) value (0.032 s−1) at an overpotential of 300 mV. These observations confirm analogous ones already reported in the literature pertaining to the potential of molecular cobalt–seleno systems as efficient OER electrocatalysts.

C2 weakens turn over frequency during melting of FexCy: insights from reactive MD simulations

The first-order phase transition plays a pivotal role in material behaviors, yet that of carbides, a type of important materials, has not been systematically studied. Herein, the melting process and...

Efficient homogeneous electrocatalytic hydrogen evolution using a Ni-containing polyoxometalate catalyst

Compound K2[Ni(H2O)6]2[V10O28]·4H2O (1) exhibits homogeneous electrocatalytic HER in an aqueous solution with a turn over frequency of 2.1 s−1 and effectively low overpotential of 127 mV at pH 2.3.