Water-Promoted Carbon-Carbon Bond Cleavage Employing a Reusable Fe Single-Atom Catalyst.

The development of methods for selective cleavage reactions of thermodynamically stable C-C/C=C bonds in a green manner is a challenging research field which is largely unexplored. Herein, we present a heterogeneous Fe-N-C catalyst with highly dispersed iron centers that allows for the oxidative C-C/C=C bond cleavage of amines, secondary alcohols, ketones, and olefins in the presence of air (O2 ) and water (H2 O). Mechanistic studies reveal the presence of water to be essential for the performance of the Fe-N-C system, boosting the product yield from <1 % to >90 %. Combined spectroscopic characterizations and control experiments suggest the singlet 1 O2 and hydroxide species generated from O2 and H2 O, respectively, take selectively part in the C-C bond cleavage. The broad applicability (>40 examples) even for complex drugs as well as high activity, selectivity, and durability under comparably mild conditions highlight this unique catalytic system.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes.

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.

Diastereoselective hydrogenation of arenes and pyridines using supported ruthenium nanoparticles under mild conditions.

A convenient and practical diastereoselective cis-hydrogenation of multi-substituted pyridines and arenes is reported. Applying a novel heterogeneous ruthenium catalyst, the corresponding piperidines and cyclohexanes are obtained in high yields (typically >80%) with a good functional group tolerance under mild conditions. The robust ruthenium supported catalyst is smoothly prepared and can be reused multiple times without activity loss.

Copper-catalysed low-temperature water-gas shift reaction for selective deuteration of aryl halides.

The introduction of deuterium atoms into organic compounds is of importance for basic chemistry, material sciences, and the development of drugs in the pharmaceutical industry, specifically for identification and quantification of metabolites. Hence, methodologies for the synthesis of selectively labelled compounds continue to be a major area of interest for many scientists. Herein, we present a practical and stable heterogeneous copper catalyst, which permits for dehalogenative deuteration via water-gas shift reaction at comparably low temperature. This novel approach allows deuteration of diverse (hetero)aryl halides with good functional group tolerance, and no reduction of the aromatic rings or other easily reducible formyl and cyano groups. Multi-gram experiments show the potential of this method in organic synthesis and medicinal chemistry.

New Insights into the Decomposition Behavior of NH4HSO4 on the SiO2-Decorated SCR Catalyst and Its Enhanced SO2-Resistant Ability.

This article illustrates the detailed decomposition behavior of NH4HSO4 on the TiO2 and TiO2-SiO2 supports, along with the effect of SiO2 addition on the sulfur resistance of the corresponding V2O5-based catalysts. For TiO2 support, sulfate species selectively occupied its surface basic hydroxyl groups, while Si-OH groups functioned as the main sites for the accommodation of NH4HSO4 over the TiO2-SiO2 mixed support, enabling its surface sulfate species with higher thermal stability. Compared with NH4 + on the TiO2 surface, NH4 + on the TiO2-SiO2 mixed support was much easier to be consumed during the heating process, hence causing some variations in the decomposition behavior of NH4HSO4. Finally, adding SiO2 enhanced the SO2 tolerance properties of the catalysts to a certain extent. When exposed to the SO2-containing flue gas, the deposition of NH4HSO4 mainly caused serious deactivation of SiO2-free catalyst, while the as-accumulated SO4 2- also contributed to the declined activity of SiO2-added catalyst. These results ensured the potential commercialization of TiO2-SiO2-based catalysts in the typical low-temperature selective catalytic reduction systems in the short run and pointed out a strategy to design new catalysts with superior activity and enhanced SO2-tolerant ability.

Structure and crystal phase transition effect of Sn doping on anatase TiO2 for dichloromethane decomposition.

Efficient removal of chlorinated volatile organic compounds (CVOCs) has received great attention because of the considerable harm that they cause to the environment and to human health. Developing novel catalysts and exploring the catalytic activation and deconstruction mechanism of CVOCs molecule are always the focus in this field. Here, a set of Sn doped TiO2 catalysts were investigated for the decomposition of dichloromethane (DCM). Rietveld refinement of the XRD patterns showed that Sn ions can uniformly disperse into TiO2 and induce the crystal transition of anatase. Meanwhile, such decorating can induce an increase in specific surface area and affect the surface oxygen vacancy concentration of these samples, which have been demonstrated by N2 adsorption and XPS, respectively. Catalytic performance tests indicated that the Sn0.2Ti0.8O2 has the best activity for DCM decomposition, and a lower CH3Cl selectivity than that of pure TiO2. Computational results suggested the dominant surface (110) of rutile Sn0.2Ti0.8O2 is more beneficial for the adsorption/dissociation of DCM molecule than that of anatase TiO2 (101). That's because the anchoring of DCM to Sn sites and electron enrichment on the surface bridge oxygen atoms of rutile Sn0.2Ti0.8O2 (110) can promote the nucleophilic substitution process for breaking of CCl bonds.

Promotional effect of doping Cu into cerium-titanium binary oxides catalyst for deep oxidation of gaseous dichloromethane.

In recent years, significant effort has been made in the development of novel catalysts for the total oxidation of chlorinated volatile organic compounds. In this work the catalytic activity of Cu doped cerium-titanium binary oxides for the oxidation of dichloromethane (DCM) have been studied for the first time. Combining catalysts characterization and activity data, it was found that Cu ions can uniformly disperse into titanium dioxide to form solid solution and induce the creation of additional surface oxygen species on the catalysts surface, while moderate amount of Ce ions are still needed for the activation of CCl. Detailed analysis of the in-situ FTIR experiment results revealed that the surface oxygen species, especially the hydroxyl groups associated with Cu ions, can promote the deep oxidation of the intermediate species formed in the nucleophilic substitution process occurred on the active sites of catalysts surface. The sample with the Cu/Ce molar ratio of 1:3 obtained a better CO2 selectivity than that reached with cerium-titanium binary oxides. Meanwhile, according to element balance analysis, removal of chlorine from the catalyst surface was also promoted by Cu doping.

Supported Bimetallic AuPd Nanoparticles as a Catalyst for the Selective Hydrogenation of Nitroarenes.

The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (MIm), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H2 that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by MIm, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by SIm was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol-1, while that of CNB to AN was found to be 31 kJ mol-1. Based on this, the yield of CAN was maximized (92%) by the lowering the reaction temperature to 25 °C.

Insight into the significant roles of microstructures and functional groups on carbonaceous surfaces for acetone adsorption.

To understand the roles of pore structures and functional groups on acetone adsorption, activated carbons (ACs) with different properties were obtained by surface modification. XRD, SEM, TEM and nitrogen adsorption were used to identify the structural characteristics of the ACs, while TG-DTA, FTIR, XPS and Boehm titration were applied to analyse the surface chemistries. The microporous surface areas showed a positive linear correlation to the acetone adsorption amounts, and increasing the carboxylic groups could improve the uptake of strongly adsorbed acetone. HNO3 modified AC (AC-N) was found to exhibit an excellent adsorption capacity of 5.49 mmol g-1, which might be attributed to the developed microporous structures and abundant carboxylic groups. The desorption activation energies (E d) of strongly adsorbed acetone on AC-N and AC were both determined to be 81.6 kJ mol-1, indicating the same adsorption sites on different activated carbons, suspected to be carboxylic groups. The possible adsorption mechanism of acetone on carbonaceous surfaces was also proposed.

Synthesis and characterization of a single phase zeolite A using coal fly ash.

Zeolitization of coal fly ash (CFA) provides a potential alternative for creating high-added-value products from this hazardous solid waste. In this work, a single phase zeolite A with high crystallinity was successfully synthesized from CFA via the alkali fusion hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR) spectroscopy, N2 physisorption, and solid-state MAS NMR spectra were applied to characterize as-synthesized zeolites. Results indicated that the type and purity of zeolite were closely related to the synthesis conditions and parameters. A well-defined cubic shape of zeolite A with a specific surface area of 43.7 m2 g-1 was obtained at a low temperature of 75 °C during hydrothermal treatment for 18 h. The ammonium cation exchange capacity (CEC) test showed an impressive value of 232.2 mmol 100 g-1 over prepared zeolite A, which was about 22 times that of the original CFA and close to commercial zeolite A. These results pave the way for the exploitation and utilization of the CFA.

Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons as effective catalysts for the selective catalytic reduction of NO with NH3.

Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons (OMCs) with various Ce/Cu ratios were synthesized by "one-pot" self-assembly method, and their activities for the selective catalytic reduction (SCR) of NO with ammonia were studied. The structural and textural properties, surface chemistry, acidity, and reducibility were investigated by various techniques. Results showed that NO conversion was greatly influenced by the weight ratio of Ce to Cu. An appropriate Ce/Cu ratio in OMCs could enhance catalytic performance; the optimal catalytic performance was obtained with Ce5Cu5-OMC. Ordered mesoporous structures were formed for all synthesized samples. When Ce or Cu was incorporated into the OMCs, the amount of surface acidic oxygen functional groups increased, thereby promoting the acidic properties of the OMCs, especially those of the Cu-rich OMCs. The surface Cu(2+) species may accelerate ammonia activation and may play an important role in SCR reaction. The temperature-programmed reduction results illustrated that the Cu-rich OMCs had better reducibility, and the appropriate Ce/Cu ratio could further enhance the redox ability of the CexCuy-OMC catalysts. The existing redox cycle (Ce(4+)+Cu(+)↔Cu(2+)+Ce(3+)) promoted the activation of NH3 and consequently improved NH3-SCR activity.

Design strategies for P-containing fuels adaptable CeO2-MoO3 catalysts for DeNO(x): significance of phosphorus resistance and N2 selectivity.

Phosphorus compounds from flue gas have a significant deactivation effect on selective catalytic reduction (SCR) DeNOx catalysts. In this work, the effects of phosphorus over three catalysts (CeO2, CeO2-MoO3, and V2O5-MoO3/TiO2) for NH3-SCR were studied, and characterizations were performed aiming at a better understanding of the behavior and poisoning mechanism of phosphorus over SCR catalysts. The CeO2-MoO3 catalyst showed much better catalytic behavior with respect to resistance to phosphorus and N2 selectivity compared with V2O5-MoO3/TiO2 catalyst. With addition of 1.3 wt % P, the SCR activity of V2O5-MoO3/TiO2 decreased dramatically at low temperature due to the impairment of redox property for NO oxidation; meanwhile, the activity over CeO2 and CeO2-MoO3 catalysts was improved. The superior NO oxidation activity contributes to the activity over P-poisoned CeO2 catalyst. The increased surface area and abundant acidity sites contribute to excellent activity over CeO2-MoO3 catalyst. As the content of P increased to 3.9 wt %, the redox cycle over CeO2 catalyst (2CeO2 ↔ Ce2O3 + O*) was destroyed as phosphate accumulated, leading to the decline of SCR activity; whereas, more than 80% NOx conversion and superior N2 selectivity were obtained over CeO2-MoO3 at T > 300 °C. The effect of phosphorus was correlated with the redox properties of SCR catalyst for NH3 and NO oxidation. A spillover effect that phosphate transfers from Ce to Mo in calcination was proposed.

The relationship between structure and activity of MoO3-CeO2 catalysts for NO removal: influences of acidity and reducibility.

The SCR activities of MoO3-CeO2 catalysts are enhanced by both Lewis and Brønsted acidities provided by surface cerium atoms and amorphous MoO3 structures, respectively, but are suppressed by stable adsorbed nitrate or nitrite species on the defect sites of CeO2.