Oxophilic Ru catalysts are active for direct deoxygenation (DDO) of phenolics, but suffer from CC hydrogenolysis and phenyl ring saturation, resulting in lower aromatic yield. Herein, we report that the DDO activity and selectivity can be improved via electronic metal-support interactions (EMSI) between Ru and irreducible ZrO2 via tuning the crystal phase (monoclinic (m) and tetragonal (t)) of ZrO2. Characterizations and density functional theory (DFT) calculations indicated that the easier formation of oxygen vacancies at the interface of Ru/m-ZrO2 than Ru/t-ZrO2 results in stronger EMSI, which facilitates higher dispersion of Ru and more Ru/ZrO2 interfacial sites. The EMSI leads to electron rich Ru at the interface, which favors the stronger adsorption of m-cresol and facilitates DDO at the Ru/ZrO2 interfacial perimeter sites. Consequently, the intrinsic reaction rate (22.07 mu mol g(-1) min(-1)) and turnover frequency (0.35 min(-1)) of toluene formation on Ru/m-ZrO2 at 350 degrees C are similar to 4.0 and similar to 1.5 times higher than those (5.56 mu molg(-1)min(-1) and 0.24 min(-1)) on Ru/t-ZrO2, respectively. Moreover, the CC hydrogenolysis and phenyl ring hydrogenation reactions catalysed by bare Ru are completely inhibited on Ru/m-ZrO2, due to the significantly improved DDO activity at the interface of Ru/ZrO2 resulting from EMSI. As a result, toluene yield of 86.3 % and aromatics yield of 90.7 % were achieved at 94.8 % m-cresol conversion on Ru/m-ZrO2. This work provides insight into the crystal phase dependent EMSI to tune the metal/oxide interface as well as its consequences on hydrodeoxygenation reaction.a

The reverse water gas shift (RWGS) reaction provides a convenient approach to convert CO2 to CO, which facilitates to achieve the goals of carbon peaking and carbon neutrality. Herein, the Cu/CeO2 catalyst prepared by a co-precipitation method using a mixture of Na2CO3 and NaOH at pH of 10 (sample Cu/CeO2-10) achieved an intrinsic reaction rate of 428.4 mmol ⋅ gcat -1 ⋅ h-1 with 100 % CO selectivity at 400 °C and CO2/H2 ratio of 1 : 4, which is much higher than Cu/CeO2 prepared by impregnation and other methods. Various characterizations showed the highest fraction of CuCeO2 solid solution in the calcined Cu/CeO2-10, and formed highly dispersed Cu clusters (~2.5 nm) on partially reduced CuCeO2 solid solution with abundant of oxygen vacancies upon reduction. The Cu and oxygen vacancies facilitates the activation of H2 and CO2, respectively, resulting in lowered H2 and CO2 reaction orders. As a result, the synergy between the two components enhanced the overall RWGS activity with lowered activation energy. Moreover, the optimal catalyst is very stable in 24 h stability test without detectable agglomeration of Cu clusters.

A combined density functional theory and microkinetic study of the ketonization of acetic acid on facets of CeO2 has been performed to understand the reaction mechanism by identifying the key reactive intermediates and active surface structures. The overall Gibbs free energies of activation, i.e., the difference between the transition state of the C–C coupling step and the surface-bound acetates, were determined to be 2.08 and 1.81 eV on CeO2(111) and 2.01 and 1.52 eV on CeO2(110) involving bidentate and monodentate acetates, respectively. Micro-kinetic analysis revealed that monodentate acetate (minor surface species) is more reactive than bidentate one (major surface species), and the (110) surface is more active than the (111) surface. The α-H abstraction step is mainly controlled by the basicity of the surface O sites, while the configuration of the adjacent Ce–O pairs determines the C–C coupling step, and together, they dictate the overall ketonization activity. Compared with CeO2(111), a stronger basicity of surface O3c on CeO2(110) facilitates efficient α-H abstraction, whereas a matching configuration of the adjacent Ce–O pairs enables facile C–C coupling, resulting in a higher ketonization activity. Detailed structural analysis revealed that the two adjacent Ce–O pairs in a rhombus configuration on the same Ce–O–Ce chain of the CeO2(110) surface form the most active ensemble for the ketonization of carboxylic acids via monodentate carboxylates. The understanding and insights will benefit the design of efficient ketonization catalysts based on transition metal oxides.

The ketonization reaction offers a convenient approach to remove oxygen and increase the carbon chain length of carboxylic acids without consuming H2. Conventional zeolites with a strong Br & oslash;nsted acid site (BAS) are very active for ketonization; however, they suffer from low ketone selectivity and fast deactivation owing to the facile secondary and tertiary reactions occurring on the strong BAS. Herein, a series of Fe-MFI zeolites (Si/Fe = 80-180) with a weaker BAS, i.e., Fe-OH-Si, than Al-MFI were prepared, characterized and tested for ketonization of propionic acid at 350 degrees C and atmospheric pressure. Compared with Al-MFI-180, although Fe-MFI-180 with its weaker BAS strength moderately reduces the activity for propionic acid ketonization (turnover frequency (TOF) of 6.97 and 3.80 min-1, respectively), it significantly reduces the activity of secondary (aldol condensation) and tertiary (aromatics formation) reactions (3-pentanone conversion TOF of 1.85 and 0.33 min-1, respectively), resulting in 3-pentanone as the dominant primary product as well as improved stability. The Fe-MFI zeolites not only showed high TOF (2.00-3.80 min-1) but also improved the selectivity for 3-pentanone and enhanced stability compared to Al-MFI with strong BAS. These results demonstrate a strategy for weakening the strength of BAS of zeolites to reduce the activity of the secondary and tertiary reactions and thereby improve the selectivity and stability of ketonization of carboxylic acids.

Ruthenium has emerged as a promising substitute for platinum toward the hydrogen evolution/oxidation reaction (HER/HOR). Herein, ruthenium/carbon composites are prepared by magnetic induction heating (300 A, 10 s) of RuCl3, RuBr3 or RuI3 loaded on hollow N-doped carbon cages (HNC). The HNC-RuCl3-300A sample consists of Ru nanoparticles (dia. 1.96 nm) and abundant Cl residues. HNC-RuBr3-300A possesses a larger nanoparticle size (≈19.36 nm) and lower content of Br residues. HNC-RuI3-300A contains only bulk-like Ru agglomerates with a minimal amount of I residues, due to reduced Ru-halide bonding interactions. Among these, HNC-RuCl3-300A exhibits the best HER activity in alkaline media, with a low overpotential of only -26 mV to reach 10 mA cm-2, even outperforming Pt/C, and can be used as the cathode catalyst for anion exchange membrane water electrolyzer (along with commercial RuO2 as the anode catalyst), producing 0.5 A cm- 2 at 1.88 V for up to 100 h, a performance markedly better than that with Pt/C. HNC-RuCl3-300A also exhibits the best HOR activity, with a half-wave potential (+18 mV) even lower than that of Pt/C (+35 mV). These activities are ascribed to the combined contributions of small Ru nanoparticles and Ru-to-halide charge transfer that weaken H adsorption.

The coordinatively unsaturated metal cations and oxygen anions on the surface of amphoteric metal oxides serve as acid and base centers, respectively, which can enable a number of acid/base catalyzed...

Catalytic reduction of CO2 to CO via reverse water-gas shift reaction on Ni-based catalysts is challenging due to the competing methanation reaction. In this work, the reduction of CO2 toward CO and CH4 has been studied by density functional theory calculation and microkinetic simulations on Ni(211) and Ag@Ni(211) surfaces. On both surfaces, direct CO2 dissociation is more favorable over formate and carboxyl pathways toward CO, and direct CO dissociation is the major pathway toward CH4. The presence of Ag shifts the d-band center of adjacent Ni atoms away from the Fermi level, resulting in reduced affinity to CO2/CO/intermediates and slightly increased barriers for most elementary steps. In particular, the apparent barrier for direct CO2 dissociation is slightly reduced by similar to 0.1 eV while direct CO dissociation is strongly inhibited by similar to 0.3 eV along the reaction coordinate, leading to CO as the predominant product on Ag@Ni(211), which agrees well with the experimental results.

Ketonization of biomass-derived carboxylic acids offers a promising approach to remove oxygen and upgrade into valuable chemicals. However, the mechanism on Br & oslash;nsted acid site (BAS) confined in micropores of zeolite remains elusive, due to the difficulty to observe the reaction intermediates experimentally and to locate the transition state via static density functional theory (DFT) calculations. Herein, ketonization of acetic acid on HBEA at 673 K was studied by metadynamics simulations based on DFT. The first reaction step was the concerted protonation and dehydroxylation of acetic acid, resulting in an electrophilic acylium cation and H2O (Delta G double dagger = 1.53 eV). The subsequent likely steps, including C & horbar;C coupling through the nucleophilic attack of acetic acid (path I), ketene (path II), and 1,1-dihydroxyethene (path III) toward acylium cation were tracked and compared. The high barriers for formation of more nucleophilic intermediates of ketene and 1,1-dihydroxyethene made the overall path II and III less favorable than the direct coupling between acetic acid and acylium cation (path I, Delta G double dagger = 2.15 eV). These results indicate that acylium cation is a key intermediate, and the C & horbar;C coupling between acetic acid and acylium cation via nucleophilic attack is the most favorable path on BAS confined in zeolite. Ketonization of acetic acid catalyzed by HBEA zeolite at 673 K was studied using metadynamics simulations based on density functional theory. The results indicate that acylium cation is the key intermediate, and the C & horbar;C coupling between acetic acid and acylium cation via nucleophilic attack is the most favorable path on BAS confined in micropores of zeolite. image

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 Cr-VI site acted as the active species for facile methane activation. The thermodynamically stable Cr-VI-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 Cr-VI oxyhydroxides, i.e., the Cr(O)(4)H-f species. The present study demonstrated that the anionic oxyl radicals formed on the anchored Cr-VI oxyhydroxides by tuning the coordination environment enabled facile methane activation and facilitated methanol production.

Molybdenum sulfides have emerged as viable alternatives to noble-metal catalysts for green hydrogen production via the hydrogen evolution reaction (HER). Herein, magnetic induction heating (MIH) is exploited for the rapid preparation of carbon-supported MoSx nanocomposites. The sample prepared at 200 A for 10 s shows an amorphous Mo3S7Cly-like structure and a low overpotential (l10) of -184 mV at 10 mA cm-2 in acidic media, whereas samples prepared at higher induction currents display a largely crystalline MoS2 structure and drastically lower HER performance. This is due to the formation of dimeric Mo6S14 moieties in amorphous MoSx that is facilitated by the loss of Cl residues during electrochemical reaction and enhanced H adsorption at both the S and Mo sites, in comparison to crystalline MoS2, as shown in First-principles calculations. These results show that MIH may be used as a powerful tool in the preparation of nonequilibrium structures as high-performance electrocatalysts.

Catalytic conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction has been identified as a promising approach for CO2 utilization and mitigation of CO2 emissions. Bare Pt shows low activity for the RWGS reaction due to its low oxophilicity, with few research works having concentrated on the inverse metal oxide/Pt catalyst for the RWGS reaction. In this work, MnOx was deposited on the Pt surface over a SiO2 support to prepare the MnOx/Pt inverse catalyst via a co-impregnation method. Addition of 0.5 wt% Mn to 1 wt% Pt/SiO2 improved the intrinsic reaction rate and turnover frequency at 400 °C by two and twelve times, respectively. Characterizations indicate that MnOx partially encapsulates the surface of the Pt particles and the coverage increases with increasing Mn content, which resembles the concept of strong metal–support interaction (SMSI). Although the surface accessible Pt sites are reduced, new MnOx/Pt interfacial perimeter sites are created, which provide both hydrogenation and C-O activation functionalities synergistically due to the close proximity between Pt and MnOx at the interface, and therefore improve the activity. Moreover, the stability is also significantly improved due to the coverage of Pt by MnOx. This work demonstrates a simple method to tune the oxide/metal interfacial sites of inverse Pt-based catalyst for the RWGS reaction.

Ketonization of propionic acid has been investigated on Lewis acidic TS-1 and Ti-Beta zeolites to understand the reaction mechanism and effects of pore topology and hydrophobicity. Characterizations showed that TS-1 and Ti-Beta (Si/Ti = 40) exhibited a similar acidity whereas TS-1 was more hydrophobic than the silanol-rich Ti-Beta. TS-1 showed higher activity, selectivity, stability and was more resistance to H2O than Ti-Beta. A combination of infrared spectroscopic, isotopic and kinetic studies showed that the molecularly adsorbed monodentate propionic acid is the most abundant reactive intermediate, and C-C coupling is the rate-determining step. The mechanism of ketonization of propionic acid at isolated tetrahedral Ti centers can be described by a Langmuir-Hinshelwood model. The turnover rate on TS-1-40 is similar to 1.3 times higher than that on Ti-Beta-40, which is consistent with the lower fitted free activation energy, i.e., the energy difference between C-C coupling transition state and two co-adsorbed propionic acids at a Ti center. The slightly lower activation enthalpy on Ti-Beta-40 than TS-1-40 is over-compensated by much larger entropy penalty, due to more silanol groups and hydrogen bonded propionic acids in close proximity to the Ti center for Ti-Beta-40, which impose additional steric hindrance to bulkier C-C coupling complex at transition state and outweigh the difference of steric hindrance of pore confinement between MFI and BEA frameworks. This work provides insight into the ketonization mechanism on Lewis acidic zeolites, and indicates that moderate pore size with hydrophobic property promotes ketonization of carboxylic acid at isolated tetrahedral Ti centers confined in zeolites.

Catalytic reverse water gas shift (RWGS) reaction has been regarded as an attractive route for the conversion of waste CO2 to valuable CO. Despite Pt being facile for hydrogenation, the low oxophilicity of Pt renders it less active for RWGS at low temperatures. Herein, Pt/SiO2 catalysts modified by WOx have been prepared to tune the WOx/Pt interfacial site for enhancing the RWGS reaction. Characterizations revealed the coverage of Pt particles by WOx clusters (polytungstate with a low polymerization degree) with an electron transfer from Pt to WOx. As a result, new WOx/Pt interfacial sites are created at the expense of surface-accessible Pt sites, which weaken CO adsorption while enhancing CO2 adsorption and activation at the interface. The intrinsic reaction rate and turnover frequency on Pt-W/SiO2 with an optimal W loading (0.5 wt %) are similar to 8 and similar to 12 times higher than those on Pt/SiO2 at 400 degrees C, with a 100% CO selectivity, pointing to an optimal WOx/Pt interfacial sites resulting from optimal coverage of Pt by WOx. Reaction kinetics, infrared spectroscopy, and density functional theory calculations collectively revealed that the RWGS shifted from the association mechanism via the carboxyl intermediate on bare Pt to the redox mechanism at the interfacial perimeter site of WOx/Pt. The interfacial sites of WOx/Pt enable both C-O breakage and H-O formation, which synergistically enhance the activity. This work demonstrated a simple strategy to tune the metal/oxide interfacial sites, which can apply to other reactions that require multiple functionalities and take place at the metal/oxide interface.

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 (TiO2, SnO2 and RuO2) 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 CH3 radical. The CH3 radical captured by the Cu site next to the radical anionic oxygen enables the coupling of CH3 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, SnO2 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.

Capturing CO2 and converting it into valuable chemicals and fuels have been regarded as a pivotal strategy in addressing the environmental challenges of ever-growing CO2 emissions. Combining CO2 capture and conversion through material or process integration can eliminate the energy-intensive steps such as separation, compression, and transportation across a wide range of space and temperatures. The flue gas at high temperatures > 300 °C can be handled with dual-function materials consisting of sorbents and catalysts. The dual-function materials combine CO2 capture and conversion through material integration, converting CO2 with reactions such as methanation, reverse water-gas shift, dry reforming of CH4, and oxidative dehydrogenation of propane. On the other hand, capturing CO2 from air directly requires a long time to collect enough CO2 for the subsequent conversion reaction. Consequently, direct air capture will likely combine with the conversion reactions in stepwise operations. The low latent heat in CO2 from direct air capture makes it more suitable for reactions at a mild condition (< 250 °C), and stepwise operation allows the separate control of the capture and conversion conditions. Herein, we reviewed recent advancements in coupling CO2 capture from flue gas and ambient air with thermal catalytic conversion. We discussed the requirements for materials, reactor configuration, and process operation for capturing and converting CO2 from these sources and proposed that future research should focus on enhancing the efficiency, scalability, and sustainability of CO2 capture and conversion technologies and optimizing the process design.

The synergy between in situ-generated Ni0 sites and Ni2P selectively boosts CH4 formation by enhancing *CO adsorption and protonation.

Using methane as a reagent to synthesize high-value chemicals and high-energy density fuels through C-C coupling has attracted intense attention in recent decades, as it avoids completely breaking all C-H bonds in CH4. In the present study, we demonstrated that the coupling of HCHO with the CH3 species from CH4 activation to produce ethanol can be accomplished on the single Pd atom-In2O3 catalyst based on the results of density functional theory (DFT) calculations. The results show that the supported single Pd atom stabilizes the CH3 species following the activation of one C-H bond of CH4, while HCHO adsorbs on the neighboring In site. Facile C-C coupling of HCHO with the methyl species is achieved with an activation barrier of 0.56 eV. We further examined the C-C coupling on other single metal atoms, including Ni, Rh, Pt, and Ag, supported on In2O3 by following a similar pathway and found that a balance of the three key steps for ethanol formation, i.e., CH4 activation, C-C coupling, and ethoxy hydrogenation, was achieved on Pd/In2O3. Taking the production of acetaldehyde and ethylene on the Pd/In2O3 catalyst into consideration, the DFT-based microkinetic analysis indicates that ethanol is the dominant product on the Pd/In2O3 catalyst. The facile C-C coupling between HCHO and dissociated CH4 makes formaldehyde a potential C1 source in the conversion and utilization of methane through an energy- and atom-efficient process.

This review summarizes recent advances in the synthesis, characterization and application of heteroatom (Ti, Zr, Sn, and Hf) Lewis acid zeolites in the conversion of biomass-derived oxygenates.

Water is typically treated as an implicit solvent in modeling electrochemical reactions in an aqueous environment. Such treatment may not be adequate, as a series of concerted or sequential proton-electron transfer steps that explicitly involve water molecules are likely to play important roles in a reaction, such as the electrochemical hydrogenation of CO2. Herein, we use the electrochemical hydrogenation of CO2 on the Sn(112) surface as a model, and employ the density functional theory (DFT) method to examine the effect of up to 12 explicit water molecules on the stability of the hydrogenation intermediates. Our results show that six water molecules are needed to account for the local interaction between an intermediate and the water solvent. Furthermore, the hydrogen bonding interaction between the explicit water molecules and intermediates causes a significant stabilization to the O-containing intermediates, such as the HCOO* and CHO* + OH* species. The inclusion of explicit water molecules also altered the prediction of the potential-limiting step from the formation of H* atoms without the explicit water molecules to the formation of H2COO* in the presence of water molecules and increased selectivity towards methane. This work provides useful insights into the electrocatalytic hydrogenation of CO2, emphasizing the importance of including explicit water molecules to account for the hydrogen bonding interaction between solvent water molecules and the reaction intermediates.

Over the past 20 years, significant effort has been devoted to advancing the modular approach to teaching chemistry laboratory courses. The development and implementation of two modules are presented here for teaching a second-semester physical chemistry laboratory course using the modular approach: an inquiry-based module concerning proteins and a project-based module concerning organic small molecules. Each module focuses on a molecular system in question and allows participating students to choose and apply various methods to study the system in different ways, according to the advantages and disadvantages of each method. The common thrust of all of the modules is to develop students' critical thinking skills, provide them a conduit to apply their knowledge to real applications, encourage them to model the approaches and behavior of practicing scientists, and excite them to initiate and pursue research opportunities. Details of implementation of this modular approach in teaching the second-semester physical chemistry laboratory for the past 11 years are provided. The assessment results indicate encouraging evidence that this two-level modular approach has achieved its goals and assisted students in choosing more research-based careers.