Role of the hydrocarbon molecular structure in CNT growth on Fe-Al catalysts.

Upgrading plastic wastes into high-value products via the thermochemical process is one of the most attractive topics. Although carbon nanotubes (CNTs) have been successfully synthesized from plastic pyrolysis gas over Fe-, Co-, or Ni-based catalysts, a deep discussion about the reaction mechanism was seldom mentioned in the literature. Herein, this work was intended to study the growth mechanism of CNTs from hydrocarbons on Fe-Al2O3 catalysts. C5-C7 hydrocarbons were used to synthesize CNTs in a high-temperature fixed-bed reactor, and the carbon products and cracked gas were analyzed in detail. The CNT yield was in the order of cyclohexane, cyclohexene > n-hexane > n-heptane > n-pentane, 1-hexene. It was proposed that CNT growth on Fe-Al2O3 catalysts was mainly determined by the yield and structure of six-membered cyclic species, which was tailored by the carbon chain length, C-C/CC bonds, and linear/cyclic structures of C5-C7 hydrocarbons. Compared with n-hexane, the six-membered rings of cyclohexane and cyclohexene promoted six-membered cyclic species formation, increasing CNT and benzene yields; the seven-membered carbon chain of n-heptane promoted methyl-six-membered cyclic species formation, decreasing CNT and benzene yields while increasing the toluene yield; the five-membered carbon chain of n-pentane and the CC bond of 1-hexene inhibited six-membered cyclic species formation, decreasing CNT and benzene yields. This work revealed the structure-activity relationship between C5-C7 hydrocarbons and CNT growth, which may direct the process design and optimization of CNT synthesis from plastic pyrolysis gas.

Fabrication of mesopore-rich HZSM-5 to boost the degradation of plastic wastes.

Plastic waste is causing serious environment pollution and its efficient disposal is attracting more and more attention. The use of catalysts not only reduced the degradation temperature of plastic wastes but also facilitated the production of valuable chemicals. Herein, mesopores were introduced into HZSM-5 zeolites by alkali and acid treatment, which was expected to eliminate the diffusion resistance caused by bulky polymer molecules and improve the catalytic activity. It was found that HZSM-5 zeolites enhanced PE, PP and PS degradation, and an increase of mesopore volume further improved the catalytic activity and reduced the activation energy. For example, the use of HZSM-5 in PP degradation decreased the activation energy from 146.9 kJ mol-1 to 93.1 kJ mol-1, and mesopore-rich HZSM-5 further decreased the activation energy to 84.0 kJ mol-1. The molecular diameter of the PP fragment was obtained by theoretical calculations, and it was close to 1.6 nm, which was significantly higher than the micropore diameter of HZSM-5 zeolites (0.5-0.6 nm) while lower than the mesopore diameter. It was concluded that the presence of mesopores provided the place and space for plastics degradation.

Constructing a Pd-Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts.

Cobalt is an alternative catalyst for furfural hydrogenation but suffers from the strong binding of H and furan ring on the surface, resulting in low catalytic activity and chemoselectivity. Herein, by constructing a Pd-Co interface in cobalt oxide-supported Pd catalysts to tailor the d-band center of Co, the concerted effort of Pd and Co boosts the catalytic performance for the hydroconversion of furfural to cyclopentanone and cyclopentanol. The increased dispersion of Pd on acid etching Co3O4 promotes the reduction of Co3+ to Co0 by enhancing hydrogen spillover, favoring the creation of the Pd-Co interface. Both experimental and theoretical calculations demonstrate that the electron transfer from Pd to Co at the interface results in the downshift of the d-band center of Co atoms, accompanied by the destabilization of H and furan ring adsorption on the Co surface, respectively. The former improves the furfural hydrogenation with TOF on Co elevating from 0.20 to 0.62 s-1, and the latter facilitates the desorption of formed furfuryl alcohol from the Co surface for subsequently hydrogenative rearrangement of the furan ring to cyclopentanone on acid sites. The resultant Pd/Co3O4-6 catalyst delivers superior activity with a 99% furfural conversion and 85% overall selectivity toward cyclopentanone/cyclopentanol. We anticipate that such a concept of tailoring the d-band center of Co via interface engineering provides novel insight and feasible approach for the design of highly efficient catalysts for furfural hydroconversion and beyond.

Optimizing oxygen vacancies through grain boundary engineering to enhance electrocatalytic nitrogen reduction.

Electrocatalytic nitrogen reduction is a challenging process that requires achieving high ammonia yield rate and reasonable faradaic efficiency. To address this issue, this study developed a catalyst by in situ anchoring interfacial intergrown ultrafine MoO2 nanograins on N-doped carbon fibers. By optimizing the thermal treatment conditions, an abundant number of grain boundaries were generated between MoO2 nanograins, which led to an increased fraction of oxygen vacancies. This, in turn, improved the transfer of electrons, resulting in the creation of highly active reactive sites and efficient nitrogen trapping. The resulting optimal catalyst, MoO2/C700, outperformed commercial MoO2 and state-of-the-art N2 reduction catalysts, with NH3 yield and Faradic efficiency of 173.7 µg h-1 mg-1cat and 27.6%, respectively, under - 0.7 V vs. RHE in 1 M KOH electrolyte. In situ X-ray photoelectron spectroscopy characterization and density functional theory calculation validated the electronic structure effect and advantage of N2 adsorption over oxygen vacancy, revealing the dominant interplay of N2 and oxygen vacancy and generating electronic transfer between nitrogen and Mo(IV). The study also unveiled the origin of improved activity by correlating with the interfacial effect, demonstrating the big potential for practical N2 reduction applications as the obtained optimal catalyst exhibited appreciable catalytic stability during 60 h of continuous electrolysis. This work demonstrates the feasibility of enhancing electrocatalytic nitrogen reduction by engineering grain boundaries to promote oxygen vacancies, offering a promising avenue for efficient and sustainable ammonia production.

Amphiphilic Polymer Capped Perovskite Compositing with Nano Zr-MOF for Nanozyme-Involved Biomimetic Cascade Catalysis.

CsPbX3 perovskite nanocrystal (NC) is considered as an excellent optical material and is widely applied in optoelectronics. However, its poor water stability impedes its study in enzyme-like activity, and further inhibits its application in biomimetic cascade catalysis. Herein, for the first time, the oxidase-like and ascorbate oxidase-like activities of an amphiphilic polymer capped CsPbX3 are demonstrated, and its catalytic mechanism is further explored. Furthermore, an all-nanozyme cascade system (multifunctional CsPbBr3 @Zr-metal organic framework (Zr-MOF) and Prussian blue as oxidase-like and peroxidase-like nanozyme) is constructed with a portable paper-based device for realizing the dual-mode (ratiometric fluorescence and colorimetric) detection of ascorbic acid in a point-of-care (POC) fashion. This is the first report on the utilization of all-inorganic CsPbX3 perovskite NC in biomimetic cascade catalysis, which opens a new avenue for POC clinical disease diagnosis.

Oxygen vacancy modulation in interfacial engineering Fe3O4 over carbon nanofiber boosting ambient electrocatalytic N2 reduction.

The oxygen vacancy modulation of interface-engineered Fe3O4 nanograins over carbon nanofiber (Fe@CNF) was achieved to improve electrocatalytic nitrogen reduction reaction (NRR) activity and stability via facile electrospinning and tuning thermal procedure. The optimal catalyst calcined at 800 ℃ (Fe@CNF-800) was endowed with abundant nanograin boundaries and optimized oxygen vacancy (Vo) concentration of iron oxides, thereby affording 37.1 µg h-1 mgcat.-1 (-0.2 V vs. reversible hydrogen electrode (RHE)) NH3 yield and rational Faraday efficiency (10.2%), with 13.6 times atomic activity enhancement compared to of that commercial Fe3O4. The interfacial effect of assembled nanograins in particles correlated with the formation of Vo and more intrinsic active sites, which is conducive to the trapping and activation of nitrogen (N2). The in-situ X-ray photoelectron spectroscopy (XPS) measurement revealed the real consumption of adsorbed oxygen when introducing N2 by the trapping effect of Vo. Density-Functional-Theory (DFT) calculation validates the promotive hydrogenation effect and elimination of hydrogen intermediate (H*) interacted with N2 transferring toward oxygen of the support. The optimal catalyst shows a lasting NRR activity at least 90 h, outperforming most reported Fe-based NRR catalysts.

Improving light absorption and photoelectrochemical performance of thin-film photoelectrode with a reflective substrate.

The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted. To increase light absorption in thin-film Fe2O3:Ti, commercial substrates such as Cu foil, Ag foil, and a mirror are adopted acting as back-reflectors and individually integrated with the Fe2O3:Ti electrode. The promotion effect of the commercial back-reflectors on the light absorption efficiency and photoelectrochemical (PEC) performance of the hydrothermally prepared Fe2O3:Ti electrodes with a variety of film thicknesses is investigated. As a result, Ag foil and the mirror show favorable and equal efficacy while the promoting effect of Cu foil is limited. In addition, the photocurrent increment achieved by the Ag back-reflector decreases linearly along with the logarithmic of the film thickness and the optimized film thickness of the Fe2O3:Ti electrode is decreased from 520 to 290 nm. The high durability of Ag foil in the alkaline electrolyte during solar light irradiation is demonstrated. Furthermore, the reflective substrate also shows a promotion effect on the BiVO4 photoanode and CuBi2O4 photocathode, as well as the unbiased photocurrent from a tandem cell constituted by TiO2 and CuBi2O4.

Density functional theory study of selective aerobic oxidation of cyclohexane: the roles of acetic acid and cobalt ion.

A computational study of cyclohexane autoxidation and catalytic oxidation to a cyclohexyl hydroperoxide intermediate (CyOOH), cyclohexanol, and cyclohexanone has been conducted using a hybrid density functional theory method. The activation of cyclohexane and O2 is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2 kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CH3COOH or (CH3COO)2Co as a catalyst reduces the energy barriers required to activate cyclohexane and O2 by 4.1 or 7.9 kcal/mol, respectively. Employing CH3COOH improves the CyOOH intramolecular dehydration process, which favors the formation of cyclohexanone. The energy barrier to the decomposition of CyOOH to CyO·, an important precursor of cyclohexanol, decreases from 35.5 kcal/mol for autoxidation to 25.9 kcal/mol for (CH3COO)2Co catalysis. (CH3COO)2Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CH3COOH and Co ion in cyclohexane oxidation. Graphical abstract Through DFT analysis of cyclohexane autoxidation and catalytic oxidation, we reveal the mechanism of the effects of CH3COOH and Co2+ on the reaction routes.

Density Functional Theory Analysis of Anthraquinone Derivative Hydrogenation over Palladium Catalyst.

A density functional theory (DFT) analysis was conducted on the hydrogenation of 2-alkyl-anthraquinone (AQ), including 2-ethyl-9,10-anthraquinone (eAQ) and 2-ethyl-5,6,7,8-tetrahydro-9,10-anthraquinone (H4 eAQ), to the corresponding anthrahydroquinone (AQH2 ) over a Pd6 H2 cluster. Hydrogenation of H4 eAQ is suggested to be more favorable than that of eAQ owing to a higher adsorption energy of the reactant (H4 eAQ), lower barrier of activation energy, and smaller desorption energy of the target product (2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone, H4 eAQH2 ). For the most probable reaction routes, the energy barrier of the second hydrogenation step of AQ is circa 8 kcal mol-1 higher than that of the first step. Electron transfer of these processes were systematically investigated. Facile electron transfer from Pd6 H2 cluster to AQ/AQH intermediate favors the hydrogenation of C=O. The electron delocalization over the boundary aromatic ring of AQ/AQH intermediate and the electron-withdrawing effect of C=O are responsible for the electron transfer. In addition, a pathway of the electron transfer is proposed for the adsorption and subsequent hydrogenation of AQ on the surface of Pd6 H2 cluster. The electron transfers from the abstracted H atom (reactive H) to a neighbor Pd atom (PdH ), and finally goes to the carbonyl group through the C4 atom of AQ aromatic ring (C4 ).