Enhancing Efficiency and High-Value Chemicals Generation through Coupling Photocatalytic CO2 Reduction with Propane Oxidation.

Conversion of CO2 into high-value chemicals using solar energy is one of promising approaches to achieve carbon neutrality. However, the oxidation of water in the photocatalytic CO2 reduction is kinetically unfavorable due to multi-electron and proton transfer processes, along with the difficulty in generating O-O bonds. To tackle these challenges, this study investigated the coupling reaction of photocatalytic CO2 reduction and selective propane oxidation using the Pd/P25 (1 wt%) catalyst. Our findings reveal a significant improvement in CO2 reduction, nearly fivefold higher, achieved by substituting water oxidation with selective propane oxidation. This substitution not only accelerates the process of CO2 reduction but also yields valuable propylene. The relative ease of propane oxidation, compared to water, appears to increase the density of photogenerated electrons, ultimately enhancing the efficiency of CO2 reduction. We further found that hydroxyl radicals and reduced intermediate (carboxylate species) played important roles in the photocatalytic reaction. These findings not only propose a potential approach for the efficient utilization of CO2 through the coupling of selective propane oxidation into propylene, but also provide insights into the mechanistic understanding of the coupling reaction.

Generating active metal/oxide reverse interfaces through coordinated migration of single atoms.

Identification of active sites in catalytic materials is important and helps establish approaches to the precise design of catalysts for achieving high reactivity. Generally, active sites of conventional heterogeneous catalysts can be single atom, nanoparticle or a metal/oxide interface. Herein, we report that metal/oxide reverse interfaces can also be active sites which are created from the coordinated migration of metal and oxide atoms. As an example, a Pd1/CeO2 single-atom catalyst prepared via atom trapping, which is otherwise inactive at 30 °C, is able to completely oxidize formaldehyde after steam treatment. The enhanced reactivity is due to the formation of a Ce2O3-Pd nanoparticle domain interface, which is generated by the migration of both Ce and Pd atoms on the atom-trapped Pd1/CeO2 catalyst during steam treatment. We show that the generation of metal oxide-metal interfaces can be achieved in other heterogeneous catalysts due to the coordinated mobility of metal and oxide atoms, demonstrating the formation of a new active interface when using metal single-atom material as catalyst precursor.

Is 1-methylcytosine a faithful model compound for ultrafast deactivation dynamics of cytosine nucleosides in solution?

1-Methylcytosine (1mCyt) is the base for nucleoside N1-methylpseudodeoxycytidine of Hachimoji nucleic acids and a frequently used model compound for theoretical studies on excited states of cytosine nucleosides. However, there is little experimental characterization of spectra and photo-dynamic properties of 1mCyt. Herein, we report a comprehensive investigation into excited state dynamics and effects of solvents on fluorescence dynamics of 1mCyt in both water and acetonitrile. The study employed femtosecond broadband time-resolved fluorescence, transient absorption, and steady-state spectroscopy, along with density functional theory and time-dependent density functional theory calculations. The results obtained provide the first experimental evidence for identifying a dark-natured ∼5.7 ps lifetime nπ* state in the ultrafast non-radiative deactivation with 1mCyt in aqueous solution. This study also demonstrates a significant effect of the solvent on 1mCyt's fluorescence emission, which highlights the crucial role of solute-solvent hydrogen bonding in altering structures and reshaping the radiative as well as nonradiative dynamics of the 1mCyt's ππ* state in the aprotic solvent compared to the protic solvent. The solvent effect exhibited by 1mCyt is distinctive from that known for deoxycytidine, indicating the need for caution in using 1mCyt for modelling the ultrafast dynamics of Cyt nucleosides in solvents with varying properties. Overall, our study unveils a deactivation mechanism that confers a high degree of photo-stability for 1mCyt in solution, shedding light on the molecular basis for solvent-induced effects on the excited state dynamics of nucleobases and derivatives.

Ultrafast excited state dynamics of isocytosine unveiled by femtosecond broadband time-resolved spectroscopy combined with density functional theoretical study.

Isocytosine, having important applications in antivirus and drug development, is among the building blocks of Hachimoji nucleic acids. In this report, we present an investigation of the excited state dynamics of isocytosine in both protic and aprotic solvents, which was conducted by a combination of methods including steady-state spectroscopy, femtosecond broadband time-resolved fluorescence, and transient absorption. These methods were coupled with density functional and time-dependent density functional theory calculations. The results of our study provide the first direct evidence for a highly efficient nonradiative mechanism achieved through internal conversion from the ππ* state of the isocytosine keto-N(3)H form occurring within subpicoseconds and picoseconds following photo-excitation. Our study also unveils a crucial role of solvent, particularly solute-solvent hydrogen bonding, in determining the tautomeric composition and regulating the pathways and dynamics of the deactivation processes. The deactivation processes of isocytosine in the solvents examined are found to be distinct from those of cytosine and the case known for isocytosine in the gas phase mainly due to different tautomeric forms involved. Overall, our findings demonstrate the high photo-stability of isocytosine in the solution and showcase the remarkable effect of covalent modification in altering the spectral character and excited state dynamics of nucleobases.

Confined Cu-OH single sites in SSZ-13 zeolite for the direct oxidation of methane to methanol.

The direct oxidation of methane to methanol (MTM) remains a significant challenge in heterogeneous catalysis due to the high dissociation energy of the C-H bond in methane and the high desorption energy of methanol. In this work, we demonstrate a breakthrough in selective MTM by achieving a high methanol space-time yield of 2678 mmol molCu-1 h-1 with 93% selectivity in a continuous methane-steam reaction at 400 °C. The superior performance is attributed to the confinement effect of 6-membered ring (6MR) voids in SSZ-13 zeolite, which host isolated Cu-OH single sites. Our results provide a deeper understanding of the role of Cu-zeolites in continuous methane-steam to methanol conversion and pave the way for further improvement.

Mechanistic Insights into Radical-Induced Selective Oxidation of Methane over Nonmetallic Boron Nitride Catalysts.

Boron-based nonmetallic materials (such as B2O3 and BN) emerge as promising catalysts for selective oxidation of light alkanes by O2 to form value-added products, resulting from their unique advantage in suppressing CO2 formation. However, the site requirements and reaction mechanism of these boron-based catalysts are still in vigorous debate, especially for methane (the most stable and abundant alkane). Here, we show that hexagonal BN (h-BN) exhibits high selectivities to formaldehyde and CO in catalyzing aerobic oxidation of methane, similar to Al2O3-supported B2O3 catalysts, while h-BN requires an extra induction period to reach a steady state. According to various structural characterizations, we find that active boron oxide species are gradually formed in situ on the surface of h-BN, which accounts for the observed induction period. Unexpectedly, kinetic studies on the effects of void space, catalyst loading, and methane conversion all indicate that h-BN merely acts as a radical generator to induce gas-phase radical reactions of methane oxidation, in contrast to the predominant surface reactions on B2O3/Al2O3 catalysts. Consequently, a revised kinetic model is developed to accurately describe the gas-phase radical feature of methane oxidation over h-BN. With the aid of in situ synchrotron vacuum ultraviolet photoionization mass spectroscopy, the methyl radical (CH3•) is further verified as the primary reactive species that triggers the gas-phase methane oxidation network. Theoretical calculations elucidate that the moderate H-abstraction ability of predominant CH3• and CH3OO• radicals renders an easier control of the methane oxidation selectivity compared to other oxygen-containing radicals generally proposed for such processes, bringing deeper understanding of the excellent anti-overoxidation ability of boron-based catalysts.

Synergetic Effect of Mo, Mg-Modified Sn-ß Over Moderate-Temperature Conversion of Hexose to Alkyl Lactate.

The thermocatalytic conversion of hexose into valuable chemicals such as methyl lactate under mild conditions is very appealing. Here, we report that Mo, Mg co-modified Sn-ß catalyst can effectively catalyze the transformation of glucose and fructose into alkyl lactate at moderate temperatures. A maximum yield of around 35% of methyl lactate was achieved from the conversion of glucose in methanol at 100°C over Sn-ß catalyst modified with 3 wt% Mo and 0.5 wt% Mg. However, up to 82.8% yield of ethyl lactate was obtained in the case of fructose in ethanol upon the same catalytic condition, suggesting a significant solvent effect. The Mo species plays a key role to enable the retro-aldol condensation of fructose, in which the competing side reactions are significantly suppressed with the assistance of neighboring Mg species probably through a synergetic effect of Lewis acid-base.

Distinct Role of Surface Hydroxyls in Single-Atom Pt1/CeO2 Catalyst for Room-Temperature Formaldehyde Oxidation: Acid-Base Versus Redox.

The development of highly efficient catalysts for room-temperature formaldehyde (HCHO) oxidation is of great interest for indoor air purification. In this work, it was found that the single-atom Pt1/CeO2 catalyst exhibits a remarkable activity with complete removal of HCHO even at 288 K. Combining density functional theory calculations and in situ DRIFTS experiments, it was revealed that the active OlatticeH site generated on CeO2 in the vicinity of Pt2+ via steam treatment plays a key role in the oxidation of HCHO to formate and its further oxidation to CO2. Such involvement of hydroxyls is fundamentally different from that of cofeeding water which dissociates on metal oxide and catalyzes the acid-base-related chemistry. This study provides an important implication for the design and synthesis of supported Pt catalysts with atom efficiency for a very important practical application-room-temperature HCHO oxidation.

Confinement-Enhanced Selective Oxidation of Lignin Derivatives to Formic Acid Over Fe-Cu/ZSM-5 Catalysts Under Mild Conditions.

Aqueous-phase oxidation by H2 O2 , known as the Fenton-type process, provides an attractive route to convert recalcitrant lignin derivatives to valuable chemicals under mild conditions. The development of this technology is, however, limited by the uncontrolled selectivity, resulting from the highly reactive nature of H2 O2 and the thermodynamically favored deep oxidation to form CO2 . This study demonstrated that formic acid could be produced with a high selectivity (up to 80.3 % at 313 K) from the Fenton-type oxidation of guaiacol and several other lignin derivatives over a bimetallic Fe-Cu catalyst supported on a ZSM-5 zeolite. Combined experimental and theoretical investigations unveiled that the micropores of the zeolite support, which contained active metal sites, preferred to adsorb C2 -C4 intermediates over formic acid because of its stronger dispersive interaction with the larger guest molecules. This confinement effect significantly suppressed the secondary oxidation of formic acid, accounting for the uniquely high formic acid selectivity over Fe-Cu/ZSM-5.

Hydrogen spillover assisted by oxygenate molecules over nonreducible oxides.

Spontaneous migration of atomic hydrogen species from metal particles to the surface of their support, known as hydrogen spillover, has been claimed to play a major role in catalytic processes involving hydrogen. While this phenomenon is well established on reducible oxide supports, its realization on much more commonly used non-reducible oxides is still challenged. Here we present a general strategy to enable effective hydrogen spillover over non-reducible SiO2 with aid of gaseous organic molecules containing a carbonyl group. By using hierarchically-porous-SiO2-supported bimetallic Pt-Fe catalysts with Pt nanoparticles exclusively deposited into the micropores, we demonstrate that activated hydrogen species generated on the Pt sites within the micropores can be readily transported by these oxygenate molecules to Fe sites located in macropores, leading to significantly accelerated hydrodeoxygenation rates on the latter sites. This finding provides a molecule-assisted approach to the rational design and optimization of multifunctional heterogeneous catalysts, reminiscent of the role of molecular coenzymes in bio-catalysis.

Shape-Dependent Performance of Cu/Cu2 O for Photocatalytic Reduction of CO2.

The photocatalytic conversion of CO2 into solar fuels or chemicals is a sustainable approach to relieve the immediate problems related to global warming and the energy crisis. This study concerns the effects of morphological control on a Cu/Cu2 O-based photocatalyst for CO2 reduction. The as-synthesized spherical Cu/Cu2 O photocatalyst exhibits higher activity than the octahedral one under visible light irradiation. The difference in photocatalytic performance between these two catalysts could be attributed to the following two factors: (1) The multifaceted structure of spherical Cu/Cu2 O favors charge separation; (2) octahedral Cu/Cu2 O only contains more positively charged (111) facets, which are unfavorable for CO2 photoreduction. The results further highlight the importance of utilizing crystal facet engineering to further improve the performance of CO2 reduction photocatalysts.

Shift of microbial turnover time and metabolic efficiency strongly regulates rhizosphere priming effect under nitrogen fertilization in paddy soil.

Microbial turnover and the decomposition of soil organic matter can be stimulated by living roots in a phenomenon known as the rhizosphere priming effect (RPE). Both the microbial turnover time (MTT) and metabolic efficiency are closely related to RPE. However, changes in MTT, metabolic efficiency and RPE in response to nitrogen (N) fertilization at different levels and the associations between these factors during plant growth are unknown. The effects of N fertilization at different levels (0, 150 and 300 kg N ha-1) on RPE and the underlying mechanisms were investigated in maize (Zea mays L.) grown in paddy soil using a 13Carbon (C) natural abundance method. The RPE varied from -1.49 to 15.93 mg C kg-1 soil day-1, with significant effects at different levels of N fertilization, growth stages and interactions between these factors. Nitrogen fertilization reduced microbial C:N imbalance and soil pH. During the plant growth periods, the RPE was initially low because the microbes preferentially utilized plant-derived C, but later increased due to trade-offs between microbial N acquisition and acidity stress alleviation under N fertilization. The soil microbes altered their MTT and metabolic efficiency with changes in the microbial community structure to maintain stoichiometric homeostasis and adapt to acidity stress. RPE was lowest whereas MTT and metabolic efficiency were highest with N fertilization at 150 kg N ha-1. Changes in MTT and metabolic efficiency explained 84.5% of the variations in the RPE, and the latter had greater impact (55.8%) than the former (28.7%). Changes in MTT and metabolic efficiency to cope with microbial resource acquisition and acidity stress under N fertilization represent an important pathway for RPE regulation in paddy soil. These findings highlight the significance of MTT and metabolic efficiency in RPE regulation for optimization of the N fertilization level to mitigate soil C losses.

Microbial mechanism of biochar addition on nitrogen leaching and retention in tea soils from different plantation ages.

The effect of biochar additions on N leaching and retention in tea soils and its microbial mechanism are still unclear. In this study, effects of biochar additions at rates of 0, 3% and 6% on N leaching, N retention and microbial responses in two tea soils with 20- and 60-year plantation ages were investigated under application with 15N-labeled urea. The results showed that cumulative mass of leached NH4+-N, NO3--N and TN was reduced by 20.9%-91.9%, 35.1%-66.9% and 40.0%-72.8% under biochar additions, respectively. The retention of TN in soil was increased by 1.2%-5.8% under biochar amendment. Fertilizer-N in the leachate was reduced by 28.8%-62.1%, while fertilizer-N retention in the soils was enhanced by 3.2%-23.9% with biochar application. Biochar addition of 6% showed the highest mitigation of N leaching and enhancement of TN retention across the two soils. Biochar additions increased soil microbial biomass and enzyme activities and changed the bacterial community composition, indicating that biochar addition increased the microbial N requirement, stimulated soil N cycling, including nitrification and denitrification processes, and enhanced microbial N immobilization in the tea soils. Those microbial responses to biochar addition were higher in 60-year-old soil relative to 20-year-old soil, leading to a higher enhancement of N retention and mitigation of N leaching. Soil pH was the prime factor that influenced soil microbes, and it strongly correlated with microbial biomass, enzyme activity, the relative abundance of dominant phyla and α-diversity indices. Therefore, the enhancement of microbial biomass, activity and shifts of bacterial community composition related to N cycling in response to biochar additions that increased the soil pH could be an important mechanism to better understand the biochar-induced N leaching mitigation and N retention enhancement in tea soils under different plantation ages.

Direct conversion of methane to formaldehyde and CO on B2O3 catalysts.

Direct oxidation of methane to value-added C1 chemicals (e.g. HCHO and CO) provides a promising way to utilize natural gas sources under relatively mild conditions. Such conversions remain, however, a key selectivity challenge, resulting from the facile formation of undesired fully-oxidized CO2. Here we show that B2O3-based catalysts are selective in the direct conversion of methane to HCHO and CO (~94% selectivity with a HCHO/CO ratio of ~1 at 6% conversion) and highly stable (over 100 hour time-on-stream operation) conducted in a fixed-bed reactor (550 °C, 100 kPa, space velocity 4650 mL gcat-1 h-1). Combined catalyst characterization, kinetic studies, and isotopic labeling experiments unveil that molecular O2 bonded to tri-coordinated BO3 centers on B2O3 surfaces acts as a judicious oxidant for methane activation with mitigated CO2 formation, even at high O2/CH4 ratios of the feed. These findings shed light on the great potential of designing innovative catalytic processes for the direct conversion of alkanes to fuels/chemicals.

Propane oxidative dehydrogenation over highly selective hexagonal boron nitride catalysts: The role of oxidative coupling of methyl.

Hexagonal boron nitride (h-BN) catalyst has recently been reported to be highly selective in oxidative dehydrogenation of propane (ODHP) for olefin production. In addition to propene, ethylene also forms with much higher overall selectivities to C2-products than to C1-products. In this work, we report that the reaction pathways over the h-BN catalyst are different from the V-based catalysts in ODHP. Oxidative coupling reaction of methyl, an intermediate from the cleavage of C─C bond of propane, contributes to the high selectivities to C2-products, leading to more C2-products than C1-products over the h-BN catalyst. This work not only provides insight into the reaction mechanisms involved in ODHP over the boron-based catalysts but also sheds light on the selective oxidation of alkanes such as direct upgrading of methane via oxidative upgrading to ethylene or CH x O y on boron-based catalysts.

Direct Coupling of Thermo- and Photocatalysis for Conversion of CO2 -H2 O into Fuels.

Photocatalytic CO2 reduction into renewable hydrocarbon solar fuels is considered as a promising strategy to simultaneously address global energy and environmental issues. This study focused on the direct coupling of photocatalytic water splitting and thermocatalytic hydrogenation of CO2 in the conversion of CO2 -H2 O into fuels. Specifically, it was found that direct coupling of thermo- and photocatalysis over Au-Ru/TiO2 leads to activity 15 times higher (T=358 K; ca. 99 % CH4 selectivity) in the conversion of CO2 -H2 O into fuels than that of photocatalytic water splitting. This is ascribed to the promoting effect of thermocatalytic hydrogenation of CO2 by hydrogen atoms generated in situ by photocatalytic water splitting.

A Strategy for the Simultaneous Synthesis of Methallyl Alcohol and Diethyl Acetal with Sn-ß.

A new strategy was developed to simultaneously produce two important chemicals, namely, methallyl alcohol (Mol) and diethyl acetal (Dal) from methacrolein in ethanol solvent at low temperature with the use of Beta zeolites modified by tin (Sn-ß catalysts). All the Sn-ß catalysts were prepared by the solid-state ion-exchange method, wherein the calcination step was conducted under different gas atmospheres. The catalyst precalcined in Ar (Sn-ß-Ar) had a reduced number of extra-framework Sn species and enabled more Sn species to be exchanged into the framework as isolated tetrahedral SnIV , enhancing the catalytic activity of the Meerwein-Ponndorf-Verley (MPV) reaction. The sodium-exchanged Sn-ß-Ar, with a reduced number of weak Brønsted acid sites, led to an even better selectivity for Mol, owing to the restriction of the side reactions such as acetalization, addition, and etherification. Under optimized catalyst and reaction conditions, the yield of Mol and Dal reached approximately 90 % and 96 %, respectively. The possible reaction pathways, along with a complex network of side products, was proposed after a detailed investigation through the use of different substrates as reactants. The fine-tuning of Sn-ß catalysts through different treatments discussed in this work is of great significance toward the understanding and manipulation of complex reactions between α,ß-unsaturated aldehydes and primary alcohols.

[MgO-Biochar for the Adsorption of Phosphate in Water].

A novel composite material MgO-biochar (MgO-BC) with the peanut shells as the precursors was successfully fabricated by loading magnesium oxide (MgO) on the surface of biochar (BC) at high temperature and in oxygen-limited atmosphere. The adsorption characteristics of the resultant adsorbent toward phosphate from aqueous solution were investigated by evaluating the influences of pH, contact time and coexisting ions. The results showed that the best phosphate adsorption onto MgO-BC happened in the pH range of 7-9, and strong acidic or basic media was unfavorable to the phosphate adsorption. Phosphate adsorption process could reach equilibrium within 540 min, and the kinetics curve could be well fitted by both pseudo-first and pseudo-second models. The related coefficients were 97.3% and 99.0%. MgO-BC exhibited highly selective capacity toward phosphate in the presence of competing Cl-, HCO3- and NO3- at 10 times higher concentration than the phosphate concentration. In addition, phosphate adsorption onto MgO-BC could be described satisfactorily by Langmuir model with a fitting coefficient of higher than 99%, and the maximal adsorption capacity calculated by Langmuir equation was 138.07 mg·g-1. The adsorption capacity of phosphate by MgO-BC was much higher than the unmodified BC and other biochar-based sorbents. Furthermore, the composite material after the adsorption of phosphate could also be used as a fertilizer into the soil. It achieved the reuse of the discarded phosphate. All the results validated that MgO-BC has a wide application prospect for the phosphate cleanup from the actual wastewater.

Hierarchical sulfur-impregnated hydrogenated TiO2 mesoporous spheres comprising anatase nanosheets with highly exposed (001) facets for advanced Li-S batteries.

In this contribution, we purposefully designed hierarchical hydrogenated TiO2 spheres (HTSs) constructed from ultrathin anatase nanosheets with highly exposed (001) facets, and further utilized them as an efficient encapsulated host of sulfur species for advanced Li-S batteries (LSBs). Strikingly, the as-fabricated hybrid S/HTSs cathode exhibited high Coulombic efficiency (>94%), exceptional long cycling performance (capacity decay of ∼0.399% per cycle at 0.5 C), and large reversible discharge capacity (∼579 mAh g(-1) at 2.0 C) at high C rates, benefiting from better electronic conductivity, smaller charge transfer resistance and strong chemical bonding between [Formula: see text] and the reduced (001) facets of HTSs, according to experimental measurements and systematical theoretical calculations. More significantly, our in-depth insights into the mechanism involved in the hybrid S/HTSs could efficiently guide future design, optimization and synthesis of other metal oxide-based matrixes with specific exposed crystal facets for next-generation advanced LSBs.

Heterostructured core-shell ZnMn2O4 nanosheets@carbon nanotubes' coaxial nanocables: a competitive anode towards high-performance Li-ion batteries.

In this study, we rationally designed a rapid, low-temperature yet general synthetic methodology for the first time, involving in situ growth of two-dimensional (2D) birnessite-type MnO2 nanosheets (NSs) upon each carbon nanotube (CNT), and we designed the subsequent phase transformation into untrathin mesoporous ZnMn2O4 NSs with a thickness of ∼2-3 nm at room temperature to efficiently fabricate heterostructured core-shell ZnMn2O4 NSs@CNT coaxial nanocables with well-dispersed and tunable ZnMn2O4 loading. The underlying insights into the low-temperature formation mechanism of the unique core-shell hybrid nanoarchitectures were tentatively proposed here. When utilized as a high-performance anode for advanced LIBs, the resultant core-shell ZnMn2O4@CNTs' coaxial nanocables (∼84.5 wt.% loading) exhibited large specific discharge capacity (∼1033 mAh g(-1)), good rate capability (∼528 mAh g(-1)) and excellent cycling stability (average capacity degradation of only ∼5.2% per cycle) at a high current rate of 1224 mA g(-1), originating from the distinct core-shell synergetic effect of fast electronic delivery and from the large electrode/electrolyte contacting surfaces/interfaces provided by three-dimensional entangling coaxial CNT-based nanonetwork topology.