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The direct conversion of methane to methanol has attracted increasing interest due to abundant and low-cost natural gas resources. Herein, by anchoring Cr-oxo/-oxyhydroxides on UiO-66 metal–organic frameworks, we demonstrate that reactive anionic oxyl radicals can be formed by controlling the coordination environment based on the results of density functional theory calculations. The anionic oxyl radicals produced at the completely oxidized CrVI site acted as the active species for facile methane activation. The thermodynamically stable CrVI-oxo/-oxyhydroxides with the anionic oxyl radicals catalyze the activation of the methane C–H bond through a homolytic mechanism. An analysis of the results showed that the catalytic performance of the active oxyl species correlates with the reaction energy of methane activation and H adsorption energies. Following methanol formation, N2O can regenerate the active sites on the most stable CrVI oxyhydroxides, i.e., the Cr(O)4Hf species. The present study demonstrated that the anionic oxyl radicals formed on the anchored CrVI oxyhydroxides by tuning the coordination environment enabled facile methane activation and facilitated methanol production. [ABSTRACT FROM AUTHOR]

[Display omitted] • C-H activation on Cr/TiO 2 is mediated by surface-stabilized hydroperoxyl. • The production of OH radicals via Fenton mechanism is energetically unfavorable. • The C-H activation proceeds through a homolytic mechanism with a barrier of 0.44 eV. • The relative strength between the acidic and basic site determines the reactivity. • The presence of water does not alter the reaction pathways. Direct conversion of methane to methanol is an attractive alternative to the indirect, energy-intensive syngas production and conversion route. Herein, we present a comprehensive density functional theory (DFT) study of converting methane directly into methanol over the Cr single atom catalyst (SAC) on anatase TiO 2 (1 0 1) surface. Cr species stabilize in the form of CrO with H 2 O 2 as oxidant, on which methane reacts with the deprotonated H 2 O 2 via an Eley–Rideal mechanism. The formation of a three-centered transition-state structure is observed in the rate-determining C H bond activation step with an activation barrier of 0.44 eV. The H 2 O 2 not only serves as the oxidant for the formation of the most stable and reactive CrO species, but also enters the coordination sphere of the Cr center and acts as a highly effective H acceptor, which significantly lowers the activation barrier for C H bond cleavage. Over different Cr-O pairs, methane C H bond activation energy is found to linearly correlate with the energy difference between the d-bond center (ε d) of Cr and p-band center of O (ε p). The presence of water changes the relative stability of the reaction intermediates but does not alter the reaction pathways. This study demonstrated the ability of Cr SACs for catalyzing direct conversion of methane to methanol under mild conditions and would stimulate further interests in designing active Cr catalysts for methane conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen site of supported CuO exhibits a characteristic of a radical anion. • The radical anionic oxygen enables homolytic C-H cleavage, resulting in a •CH 3. • The CH 3 radical captured by the Cu site enables the CH 3 -OH coupling to form CH 3 OH. • SnO 2 offers a balanced reactivity for C-H activation and C-O formation. Direct conversion of methane into methanol is an attractive strategy for the production of manifold value-added chemicals. Herein, we investigated the conversion of methane to methanol over CuO supported on the rutile metal oxides (TiO 2 , SnO 2 and RuO 2) based on results of density functional theory (DFT) calculations. The results show that the oxygen site of the supported CuO exhibits the characteristics of a radical anion. This radical anionic oxygen site enables homolytic C-H cleavage by abstracting the hydrogen atom, resulting in a CH 3 radical. The CH 3 radical captured by the Cu site next to the radical anionic oxygen enables the coupling of CH 3 and OH to form a C-O bond, resulting in methanol. The free energy of activation for C-H activation and C-O formation were found to correlate linearly with the p band center of the radical anionic oxygen, but the slope has the opposite signs, i.e., a lower free energy of activation for C-H scission corresponds to a higher free energy formation for C-O formation. Among rutile oxides studied, SnO 2 offers a balanced reactivity for C-H activation and C-O formation. These findings demonstrate the presence of the radical anionic oxygen on rutile oxide-supported CuO catalyst and their crucial role in regulating the reactivity for direct methane to methanol conversion. The mechanistic insights from this study will benefit the development of supported copper oxide catalysts for effective methane conversion. [ABSTRACT FROM AUTHOR]

Understanding structural transformation and phase transition accompanying reactions in a solid as a catalyst or oxygen carrier is important to the design and optimization of many catalytic or chemical looping reaction processes. Herein, we combined density functional theory calculation with the stochastic surface walking global optimization approach to track the structural transformation accompanying the reduction of CuO upon releasing oxygen. We then used machine learning (ML) methods to correlate the structural properties of CuOx with varying x. By decomposing a reduction step into oxygen detachment and structural reconstruction, we identified two types of pathways: (1) uniform reduction with minimal structural changes; (2) segregated reduction with significant reconstruction. The results of ML analysis showed that the most important feature is the radial distribution functions of Cu–O at a percentage of oxygen vacancy [C(OV)] < 50% and Cu–Cu at C(OV) > 50% for CuOx formation. These features reflect the underlying physicochemical origin, i.e., Cu–O breaking and Cu–Cu formation in the respective stage of reduction. Phase diagram analysis indicates that CuO will be reduced to Cu2O under a typical oxygen uncoupling condition. This work demonstrates the complexity of solid structural transformation and the potential of ML methods in studying solid state materials involved in many chemical processes. [ABSTRACT FROM AUTHOR]

Cellulose is one of the main raw materials for production of green ethanol, but the presence of the growth inhibitor furfural in non-detoxified lignocellulosic hydrolysates often seriously affects their utilization. In a previous study, we obtained strains of Candida glycerinogenes that were tolerant to furfural, but at concentrations above 2.5 g L−1 there was a significant increase in the growth lag phase. In this work, transcription factor genes (SEF1, STB5, CAS5, and ETP1) associated with furfural tolerance were identified and employed to obtain modified strains permitting ethanol fermentation of concentrated and non-detoxified cellulose hydrolysates containing more than 2.5 g L−1 furfural. Tolerance to furfural could be increased to 4.5 g L−1 by overexpression of either STB5 or ETP1, which have different regulation patterns. Moreover, in non-detoxified and concentrated cellulose hydrolysate, overexpression of ETP1 significantly shortened the growth lag phase and ethanol fermentation time was reduced by 17–20%. In batch fermentations fed with concentrated non-detoxified lignocellulose hydrolysate, ethanol productivity and maximum ethanol concentration reached 2.4 g L−1 h−1 and 72.5 g L−1, increases of 26.1% and 6.6%, respectively. The results provided a route for the economic use of lignocellulose for chemical production. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT is conducted for CH 3 OH formation on the Cu oxides surfaces. • Heterolytic cleavage of the C–H bond of CH 4 is preferred at the Cu–O site. • Synergetic C–H activation and C–O formation for CH 4 to CH 3 OH on CuO x is exhibited. • CH 3 diffusion plays an important role in the synergetic effect of Cu–O and O–O. Direct methane to methanol conversion is desirable but difficult to implement due to the inertness of methane and unattainable matching oxidant. The capability of Cu oxides releasing lattice oxygen makes it a potential oxidant to facilitate the conversion. Herein, the mechanism of methane to methanol on the surfaces of CuO x has been studied using density functional theory calculations. Heterolytic cleavage of the C–H bond is preferred at the Cu–O site whereas methanol formation from dissociated CH 3 and H on surface O can take place over either Cu–O or O–O site. On CuO(1 ¯ 1 1), methane activation at the Cu–O site and methanol formation over the O–O site synergistically enable the selective oxidation of methane to methanol. In contrast, the formation of methanol on the O-deficient surfaces is a result of direct coupling of CH 3 on Cu and OH formed from of H adsorbed on the surface O site. Microkinetics analysis confirms the synergistic effect of Cu–O and O–O on CuO(1 ¯ 1 1) for methanol formation in a temperature range of 473–648 K. These findings demonstrate the feasibility of selective oxidation of methane to methanol with the surface lattice oxygen of CuO x and help to design the CuO x -based oxygen carriers and/or catalysts. [ABSTRACT FROM AUTHOR]

Controllable interfacial polymerization (IP) is eminently desirable for the preparation of high-performance nanofiltration (NF) membranes to address the worldwide water scarcity. Herein, we report a facile and versatile approach to prepare novel polyamide (PA) NF membranes via a hydrogel-assisted IP process. The piperazine (PIP) diffusion was precisely controlled by tailoring the viscosity of the introduced chitosan/polyvinyl alcohol (CS/PVA) hydrogel via adjusting the hydrogel composition and crosslinking degree. Due to the synergistic effect of the decreased thickness and improved surface hydrophilicity of the PA layer formed atop hydrogel, the hydrogel-regulated thin film composite (TFC-hg) membrane exhibited a high water permeance of 15.5 L m−2 h−1 bar−1, which was 2.5 times of that of the control membrane. Meanwhile, the TFC-hg membrane achieved a Na 2 SO 4 rejection of 99.1 % due to the highly cross-linked PA separation film. This work offers a simple and highly effective strategy for constructing high-performance TFC NF membranes toward efficient water treatment. [Display omitted] • Hydrogel intermediate layer was used for nanofiltration membrane preparation. • The hydrogel layer retarded the diffusion of amine monomers during IP. • The relation among hydrogel viscosity, amine diffusion and PA thickness was built. • The optimal NF membrane achieved high water permeability and salt rejection. [ABSTRACT FROM AUTHOR]