Quinoline, Indole, and Isogranatanine Alkaloids from Malayan Leuconotis eugeniifolia.

Nine new alkaloids, eugeniinalines A-H (1-8) and (+)-eburnamenine N-oxide (9), comprising one quinoline, six indole, and two isogranatanine alkaloids, were isolated from the stem-bark extract of the Malayan Leuconotis eugeniifolia. The structures and absolute configurations of these alkaloids were established based on the analysis of the spectroscopic data, GIAO NMR calculations, DP4+ probability analysis, TDDFT-ECD method, and X-ray diffraction analysis. Eugeniinaline A (1) represents a new pentacyclic quinoline alkaloid with a 6/6/5/6/7 ring system. Eugeniinaline G (7) and its seco-derivative, eugeniinaline H (8), were the first isogranatanine alkaloids isolated as natural products. The known alkaloids leucolusine (10) and melokhanine A (11) were found to be the same compound, based on comparison of the spectroscopic data of both compounds, with the absolute configuration of (7R, 20R, 21S). Eugeniinalines A and G (1 and 7) showed cytotoxic activity against the HT-29 cancer cell line with IC50 values of 7.1 and 7.2 µM, respectively.

Unsaturated Penta-Coordinated Mo5c5+ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers.

Selective oxidation of C-H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo5+ species are effective for these reactions, but the accurate identification of the structure of active Mo5+ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo5c5+ with a high fraction in MoOx fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo5c5+ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C-H bond in CH3O* at lower temperatures.

Repair of missing linker defects in UiO-66 by a "molecular patch" boosting the 1-hexene hydroformylation reaction.

Fabrication of MOFs with missing linker defects has become a common means to improve catalytic performances. However, the stability of the defects deserves to be investigated first. In this work, we found that 3-phenylpropionaldehyde (3-PPA) could coordinate with the missing linker defects of UiO-66, which highlighted the instability of the missing linker defects. 3-PPA acted as a molecular patch for the modification of the Rh/UiO-66 catalyst, which repaired the open Zr6 sites and resulted in a remarkable improvement of aldehyde selectivity (from 50.0% to 89.6%) in 1-hexene hydroformylation.

Correction: Controlling CO2 hydrogenation selectivity by Rh-based catalysts with different crystalline phases of TiO2.

Correction for 'Controlling CO2 hydrogenation selectivity by Rh-based catalysts with different crystalline phases of TiO2' by Fenghai Cao et al., Chem. Commun., 2022, 58, 4219-4222, https://doi.org/10.1039/D2CC00472K.

Eugeniifoline, a Pentacyclic Indole Alkaloid from Leuconotis eugeniifolia, and Configurational Revision of Synthetic Eugeniifoline Isolated from a Diversity-Enhanced Extract.

Eugeniifoline (1), a pentacyclic indole alkaloid with a five-membered ring E, was isolated for the first time as a natural product from the stem-bark extract of Leuconotis eugeniifolia. Eugeniifoline (1) was previously reported as a synthetic product from a diversity-enhanced extract, but with the configuration at C-21 reported as S (1a). The configuration at C-21 was revised to R as shown in 1, based on the NOE data, GIAO NMR calculations, and DP4+ probability analysis, as well as the TDDFT-ECD method.

Controlling CO2 hydrogenation selectivity by Rh-based catalysts with different crystalline phases of TiO2.

A series of Rh-based catalysts with various crystalline phases (p25, anatase, and rutile) were prepared via the incipient-wetness impregnation method. It was found that these catalysts had different metal-support interactions. Hence, 1%Rh/p, 1%Rh/r, and 1%Rh/a exhibited methane, CO, and methanol selectivity, respectively.

Selective oxidation conversion of methanol/dimethyl ether.

As important platform compounds, methanol and dimethyl ether (DME) are vital bridges between the coal chemical, petrochemical and fine chemical industries. At present, the synthesis of methanol/DME has been industrialized, and the production capacity is much larger than the market demand. Therefore, the conversion of methanol/DME into more valuable chemicals is an important and significant topic. The synthesis of high value-added oxygenated chemicals and diesel oil additives from methanol/DME by an oxidation method has attracted substantial attention due to it being green and environmentally friendly and having good atom economy. In this feature article, we have summarized the recent advances in the synthesis of formaldehyde, methyl formate, dimethoxymethane, and polyoxymethylene dimethyl ethers, from the selective oxidation of methanol/DME, and further discussed the adsorption and activation of reactant molecules, selective cleavage of C-O, C-H or O-H bonds in methanol/DME molecules and the C-O chain growth in the target products. In the end, major challenges and future prospects are proposed from the viewpoint of catalyst design and application. It is expected that this feature article will provide theoretical guidance for the activation and cleavage of C-O, C-H, or O-H bonds in other small molecules of alcohol/ether as well as low-carbon alkanes, so as to synthesize high value-added chemicals.

Biomass-Based Carbon-Supported Sulfate Catalyst for Efficient Synthesis of Dimethoxymethane from Direct Oxidation of Dimethyl Ether.

The synthesis of dimethoxymethane (DMM) from direct oxidation of dimethyl ether (DME) is a green and competitive route with good atomic economy and low carbon emission and is also an urgent need. In this work, biomass-based carbon-supported sulfate catalysts were designed and prepared for the efficient synthesis of DMM from DME oxidation. The prepared carbon support from cellulose displayed much larger specific surface area and a developed microporous structure, which effectively benefited a high dispersion of sulfate components, leading to mainly weak acid sites and more oxygen functional groups on the catalyst surface. The Ti(SO4)2/PC-H2SO4 catalyst exhibits excellent performance for DME oxidation with DMM1-2 selectivity up to 96.7%, and DMM selectivity reaches 89.1%, notably higher than that of previously reported results. The distinctive surface structure and chemical properties of the carbon support have important impacts on the dispersion state of sulfate species, affecting the acidic and redox properties of the catalysts.

Oxidative coupling of methane over Mo-Sn catalysts.

A novel Mo-Sn catalyst for the oxidative coupling of methane was designed using a hydrothermal method. At 650 °C, the conversion of methane was 8.6% and the selectivity of the C2 hydrocarbons reached as high as 98.1% over the Mo1Sn3 catalyst, with a CO2 selectivity of only 0.8%. We demonstrated that the deep oxidation of methane to CO2 was further inhibited due to the synergistic effects of moderately strong basic sites and reactive oxygen species on the catalyst surface.

Hydrogenation of CO2 into aromatics over a ZnCrOx-zeolite composite catalyst.

A ZnCrOx-ZnZSM-5 composite catalyst was used for CO2 hydrogenation into hydrocarbons especially aromatics (Aro). 81.1% Aro selectivity in C5+ hydrocarbons (mainly C5-11) was obtained at 320 °C, corresponding to 19.9% CO2 conversion, 29.8% total hydrocarbons (HCt) selectivity and 69.7% C5+ selectivity in HCt. Our optimized STY of Aro is the highest ever reported.

Visible-Light Direct Conversion of Ethanol to 1,1-Diethoxyethane and Hydrogen over a Non-Precious Metal Photocatalyst.

Converting renewable biomass and their derivatives into chemicals and fuels has received much attention to reduce the dependence on fossil resources. Photocatalytic ethanol dehydrogenation-acetalization to prepare value-added 1,1-diethoxyethane and H2 was achieved over non-precious metal CdS/Ni-MoS2 catalyst under visible light. The system displays an excellent production rate and high selectivity of 1,1-diethoxyethane, 52.1 mmol g-1 h-1 and 99.2 %, respectively. In-situ electron spin resonance, photoluminescence spectroscopy and transient photocurrent responses were conducted to investigate the mechanism. This study provides a promising strategy for a green application of bioethanol.

Ultrathin Visible-Light-Driven Mo Incorporating In2 O3 -ZnIn2 Se4 Z-Scheme Nanosheet Photocatalysts.

Inspired by natural photosynthesis, the design of new Z-scheme photocatalytic systems is very promising for boosting the photocatalytic performance of H2 production and CO2 reduction; however, until now, the direct synthesis of efficient Z-scheme photocatalysts remains a grand challenge. Herein, it is demonstrated that an interesting Z-scheme photocatalyst can be constructed by coupling In2 O3 and ZnIn2 Se4 semiconductors based on theoretical calculations. Experimentally, a class of ultrathin In2 O3 -ZnIn2 Se4 (denoted as In2 O3 -ZISe) spontaneous Z-scheme nanosheet photocatalysts for greatly enhancing photocatalytic H2 production is made. Furthermore, Mo atoms are incorporated in the Z-scheme In2 O3 -ZISe nanosheet photocatalyst by forming the MoSe bond, confirmed by X-ray photoelectron spectroscopy, in which the formed MoSe2 works as cocatalyst of the Z-scheme photocatalyst. As a consequence, such a unique structure of In2 O3 -ZISe-Mo makes it exhibit 21.7 and 232.6 times higher photocatalytic H2 evolution activity than those of In2 O3 -ZnIn2 Se4 and In2 O3 nanosheets, respectively. Moreover, In2 O3 -ZISe-Mo is also very stable for photocatalytic H2 production by showing almost no activity decay for 16 h test. Ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy, transient photocurrent spectra, and electrochemical impedance spectroscopy reveal that the enhanced photocatalytic performance of In2 O3 -ZISe-Mo is mainly attributed to its widened photoresponse range and effective carrier separation because of its special structure.

Effects of calcination and reduction temperature on the properties of Ni-P/SiO2 and Ni-P/Al2O3 and their hydrodenitrogenation performance.

A series of SiO2-supported and γ-Al2O3-supported nickel phosphides were prepared by temperature-programmed reduction (TPR) with different calcination and reduction temperatures. The prepared catalysts were characterized by XRD, BET, H2-TPR, CO titration and HRTEM. The crystal phase and CO uptake content were influenced by calcination and reduction temperature. The catalytic performance of various catalysts was tested in quinoline hydrodenitrogenation and exhibited considerable differences. The quinoline HDN activity of SiO2-supported nickel phosphides decreases with increase of calcination and reduction temperature. In contrast to SiO2-supported samples, the ability to remove nitrogen of γ-Al2O3-supported samples increases with reduction temperature.

Synthesis of isoalkanes over a core (Fe-Zn-Zr)-shell (zeolite) catalyst by CO2 hydrogenation.

A kind of core-shell catalyst with Fe-Zn-Zr as the core and a zeolite (HZSM-5, Hbeta, and HY) as the shell was synthesized by a simple cladding method. The catalyst has an obvious confinement effect on the synthesis of isoalkanes by CO2 hydrogenation. Especially, the Fe-Zn-Zr@HZSM-5-Hbeta catalyst with a double-zeolite shell exhibits an extraordinary high i-HC/t-HC ratio.

Facilely synthesized H-mordenite nanosheet assembly for carbonylation of dimethyl ether.

Hard coke blockage of micropores of acidic zeolites generally causes serious catalytic deactivation for many chemical processes. Herein, we report a facile method to synthesize H-mordenite nanosheet assemblies without using any template agent. The assemblies exhibit the high catalytic activity for carbonylation of dimethyl ether because of their large quantity of framework Brønsted acids. The specific morphology of the nanosheet unites improves mass diffusion for both reactants and products. Consequently, the coke precursor species can readily migrate from the micropores to the external surface of the assemblies, inducing the improved catalytic stability through inhibiting hard coke formation in frameworks.

Tuning interactions between zeolite and supported metal by physical-sputtering to achieve higher catalytic performances.

To substitute for petroleum, Fischer-Tropsch synthesis (FTS) is an environmentally benign process to produce synthetic diesel (n-paraffin) from syngas. Industrially, the synthetic gasoline (iso-paraffin) can be produced with a FTS process followed by isomerization and hydrocracking processes over solid-acid catalysts. Herein, we demonstrate a cobalt nano-catalyst synthesized by physical-sputtering method that the metallic cobalt nano-particles homogeneously disperse on the H-ZSM5 zeolite support with weak Metal-Support Interactions (MSI). This catalyst performed the high gasoline-range iso-paraffin productivity through the combined FTS, isomerization and hydrocracking reactions. The weak MSI results in the easy reducibility of the cobalt nano-particles; the high cobalt dispersion accelerates n-paraffin diffusion to the neighboring acidic sites on the H-ZSM5 support for isomerization and hydrocracking. Both factors guarantee its high CO conversion and iso-paraffin selectivity. This physical-sputtering technique to synthesize the supported metallic nano-catalyst is a promising way to solve the critical problems caused by strong MSI for various processes.

NO adsorption behaviors of the MnOx catalysts in lean-burn atmospheres.

NO(x) emission control of lean-burn engines is one of the great challenges in the world. Herein, the MnOx model catalysts with the different calcination temperatures were synthesized to investigate their NO adsorbability for lean-burn exhausts. The transformation from (ß-)MnO2 to (α-)Mn2O3 following the increased calcination temperatures was evidenced from the viewpoint of the local atomic level. Among these samples, the one calcined at 550 °C containing the single α-Mn2O3 phase displayed the best NO adsorbability: NO was mainly adsorbed in the forms of NO/nitrites and NO2/nitrates at the low and high temperatures, respectively; the NO oxidation ability displayed the volcano-shape following the increased operating temperatures, and reached the maximum, i.e. 92.4% of the NO-to-NO2 conversion, at 250 °C. Moreover, this sample presented the efficiently reversible NO adsorption/desorption performance in alternative lean-burn/fuel-rich atmospheres, due to the weakly bonded NO(x) on it. The superficial oxygen species plays a critical role for the NO oxidation over α-Mn2O3. The consumed superficial oxygen could be further compensated by the gaseous and lattice oxygen therein. Our findings show that the α-Mn2O3 material is a promising NO(x) adsorber for lean-burn exhausts even at low operating temperatures.

Copper nanoparticles decorated inside or outside carbon nanotubes used for methyl acetate hydrogenation.

Copper nanoparticles loaded inside or outside carbon nanotubes (CNTs) were prepared by a simple wet chemistry method. The structures and physicochemical properties of the obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Methyl acetate (MA) hydrogenation forming methanol and ethanol was chosen as the application to explore the catalytic performances of copper inside and outside CNTs. The reaction results indicated that the catalytic activity of Cu-inside-CNTs catalyst was significantly higher than that of Cu-outside-CNTs because of the space confined effects. Furthermore, the influences of Cu content on CNTs to the catalytic performance were also investigated.

An introduction of CO2 conversion by dry reforming with methane and new route of low-temperature methanol synthesis.

Carbon dioxide is one of the highest contributors to the greenhouse effect, as well as a cheap and nontoxic building block for single carbon source chemistry. As such, CO2 conversion is one of most important research areas in energy and environment sciences, as well as in catalysis technology. For chemical conversion of CO2, natural gas (mainly CH4) is a promising counterpart molecule to the CO2-related reaction, due to its high availability and low price. More importantly, being able to convert CH4 to useful fuels and molecules is advantageous, because it is also a kind of "greenhouse effect" gas, and can be an energy alternative to petroleum oil. In this Account, we discuss our development of efficient catalysts with precisely designed nanostructure for CO2 reforming of CH4 to produce syngas (mixture of CO and H2), which can then be converted to many chemicals and energy products. This new production flow can establish a GTL (gas-to-liquid) industry, being currently pushed by the shale gas revolution. From the viewpoint of GTL industry, developing a catalyst for CO2 reforming of CH4 is a challenge, because they need a very high production rate to make the huge GTL methane reformer as small as possible. In addition, since both CO2 and CH4 give off carbon deposits that deactivate non-precious metallic catalysts very quickly, the total design of catalyst support and supported metallic nanoparticles is necessary. We present a simple but useful method to prepare bimodal catalyst support, where small pores are formed inside large ones during the self-organization of nanoparticles from solution. Large pores enhance the mass transfer rate, while small pores provide large surface areas to disperse active metallic nanoparticles. More importantly, building materials for small pores can also be used as promoters or cocatalysts to further enhance the total activity and stability. Produced syngas from methane reforming is generally catalytically converted in situ via one of two main routes. The first is to use Fischer-Tropsch synthesis (FTS), a process that catalytically converts syngas to hydrocarbons of varying molecular weights. The second is methanol synthesis. The latter has better atomic economy, since the oxygen atom in CO is included in the product and CO2 can be blended into syngas as a reactant. However, production of methanol is very inefficient in this reaction: only 10-15% one-pass conversion typically at 5.0-10.0 MPa and 523-573 K, due to the severe thermodynamic limitations of this exothermal reaction (CO + 2H2 = CH3OH). In this Account, we propose and develop a new route of low-temperature methanol synthesis from CO2-containing syngas only by adding alcohols, including methanol itself. These alcohols act as homogeneous cocatalysts and the solvent, realizing 70-100% one-pass conversion at only 5.0 MPa and 443 K. The key step is the reaction of the adsorbed formate species with alcohols to yield ester species at low temperatures, followed by the hydrogenation of ester by hydrogen atoms on metallic Cu. This changes the normal reaction path of conventional, high-temperature methanol synthesis from formate via methoxy to methanol.

Facile synthesis of H-type zeolite shell on a silica substrate for tandem catalysis.

A new class of silica-based zeolite capsule catalyst was readily prepared employing a dual-layer method under close-to-neutral conditions. In a tandem catalysis process, the precisely controlled synthesis of dimethyl ether was realized. This new concept of H-type zeolite shell preparation and application represents a powerful approach for preparing high-performance, multifunctional catalysts.