Metal-support Interaction Effect Research Articles

Synergistic Effect between Zr-MOF and Phosphomolybdic Acid with the Promotion of TiF4 Template.

Metal-Organic Framework (MOF) materials are often modified or functionalized, and then the crystal size and morphology of MOF materials are changed. In the process of preparing UiO-66 confined phosphomolybdic acid (PMA) composites (PU), the TiF4-modified PU (PMA + UiO-66) composite catalyst (TiF4-PU) was successfully synthesized by adding titanium tetrafluoride, and the catalytic desulfurization activity was excellent. Similarly, the reaction mechanism was investigated by means of infrared spectroscopy, Raman spectroscopy, XPS, and UV/Vis spectroscopy. The results show that the addition of TiF4 not only changes the appearance and color of the catalyst, but also changes the valence distribution of the elements in the catalyst. The number of oxygen vacancies in the MOF increases due to the addition of TiF4, and more electrons are transferred from the Zr-MOF to PMA to form more Mo5+, which improved the performance of oxidative desulfurization in comparison. Thus, a stronger strong metal-support interaction (SMSI) effect is observed for TiF4-modified PU catalysts. In addition, the quenching experiment of free radicals shows that ·OH radical is the main active substance in the oxidative desulfurization reaction over TiF4-PU catalyst.

Combing strong metal support interaction and N doping to improve the durability of 3D carbon nanosheets supported Pt catalyst

In this work, for the first time, MgFe2O4 (MFO) is used to stabilize the N-doped 3D carbon nanosheets supported platinum catalysts (Pt/MFO/NPC). The spherical MFO nanoparticles are randomly dispersed on the surface of the 3D carbon nanosheets, with Pt particles uniformly distributed on them. The Pt/MFO/NPC catalyst possesses excellent stability and methanol tolerance in alkaline solution. The current retention reaches 87.0% after 20,000 s of stability test, which is significantly higher than that of commercial Pt/C (46.9%). In addition, the onset potential (Eonset) and half-wave potential (E1/2) values of Pt/MFO/NPC are larger than that of the commercial contrast, implying the improved kinetics of the Oxygen reduction reaction (ORR). The excellent catalytic activity and stability of Pt/MFO/NPC can be attributed to the combined effect of N-doping and strong metal-support interaction (SMSI) between MFO and Pt.

Electronic Oxide-Metal Strong Interaction (EOMSI).

Strong metal-support interaction of supported metal catalysts is an important concept to describe the effect of metal-support interactions on the structures and catalytic performances of supported metal particles. By using an example of CeOx adlayers supported on Ag nanocrystals, herein a concept of electronic oxide-metal strong interaction (EOMSI) is put forward; this interaction significantly affects the electronic structures of oxide adlayers through metal-to-oxide charge transfer. The EOMSI can stabilize oxide adlayers in a low oxidation state under ambient conditions, which individually are not stable; moreover, the oxide adlayers experiencing the EOMSI are resistant to high-temperature oxidation in air to a certain extent. Such an EOMSI concept helps to generalize the strong influence of oxide-metal interactions on the structures and catalytic performance of oxide/metal inverse catalysts, which have been attracting increasing attention.

Reaction-Induced Strong Metal-Support Interactions between Metals and Inert Boron Nitride Nanosheets.

Encapsulation of metal nanocatalysts by support-derived materials is well known as a classical strong metal-support interaction (SMSI) effect that occurs almost exclusively with active oxide supports and often blocks metal-catalyzed surface reactions. In the present work this classical SMSI process has been surprisingly observed between metal nanoparticles, e.g., Ni, Fe, Co, and Ru, and inert hexagonal boron nitride (h-BN) nanosheets. We find that weak oxidizing gases such as CO2 and H2O induce the encapsulation of nickel (Ni) nanoparticles by ultrathin boron oxide (BOx) overlayers derived from the h-BN support (Ni@BOx/h-BN) during the dry reforming of methane (DRM) reaction. In-situ surface characterization and theory calculations reveal that surface B-O and B-OH sites in the formed BOx encapsulation overlayers work synergistically with surface Ni sites to promote the DRM process rather than blocking the surface reactions.

Hydrodechlorination and deep hydrogenation on single-palladium-atom-based heterogeneous catalysts

Halophenols are widely present in wastewater and groundwater, which threaten global water safety and human health. Importantly, hydrodechlorination (HDC) via heterogeneous catalysis is efficient and environmentally friendly. To further improve the catalytic performance and atomic economy, Pd-based single atom catalysts (SACs) were prepared through electrostatic attraction and used in the catalytic HDC for the first time. By substituting different defect-rich supports, the coordination environments of atomically dispersed Pd-atoms were mediated with different catalytic performance. The results demonstrate that the Pd/CeO2 SACs have the highest HDC activity and remain stable during cycle tests. The moderately intensive metal-support interactions (MIMSI) effect was identified as a critical factor for the higher activity of SACs, unlike the traditional strong metal-support interaction effect. The HDC process on Pd SACs was further investigated by combining kinetic experiments with density functional theory calculations, which facilitated the recognition of HDC intermediates and an understanding of the reaction mechanism.

Uniformly sized Pt nanoparticles dispersed at high loading on Titania nanotubes

A range of Pt loadings (0.9–21.5 wt. %) on titania nanotubes (TNT) catalysts were prepared with a view to address metal-support interaction effects on Pt nanoparticles (size, dispersion, shape) and were prepared by a vapor-phase impregnation method using Pt(acac). The reduced catalysts were characterized by XRD, TEM, H2-TPD, CO adsorption FTIR and examined as catalysts in naphthalene hydrogenation. Pt nanoparticles have a very uniform size between 1.4–2.2 nm for Pt loadings 0.9–21.5 wt% as indicated by TEM, H2-TPD and CO-adsorption FTIR. A strong metal-support interaction between Pt and TNT support hinder Pt nanoparticles to agglomerate into larger particles, even at high Pt loadings. Both Pt edge sites and exposed surface total Pt sites are highest at 10.2 wt.% Pt loading and parallels naphthalene hydrogenation activity which peaks at this loading.

Electrochemically Enhancing Nanostructured Fe-Oxide/Co3O4 for the Reverse Water Gas Shift Reaction

The abundant amount of CO2 in the atmosphere is a valuable resource that when managed correctly can replace energy from the fossil fuel industry and provide a carbon-neutral solution that will reduce the impacts of the climate and ecological crisis[1]. This is achieved by reducing CO2 with hydrogen (H2) through the reverse water gas shift (RWGS) reaction to produced carbon monoxide (CO). CO then acts as a source molecule in the Fischer-Tropsch synthesis to manufacture hydrocarbon fuels. Due to the high stability of the CO2 molecule, significant thermal energy is required to undertake the reaction. Iron-oxide (FeOx) has been shown to be an active and thermally stable catalysts towards the RWGS reaction. FeOx (iron-oxide) nanowires are fabricated through the polyol reduction method and have been characterized through scanning transmission electron microscopy (STEM) analysis[2]. Following the wet deposition method, the Fe nanowires are finely dispersed on cobalt-oxide (Co3O4) to act as a support and semi-conductor. The dispersion of Fe on Co3O4 enhances the electronic properties of the catalyst through the metal-support interaction (MSI) effect[3]. The MSI entails the back spillover of promoting oxygen (Oδ-) ionic species from Co3O4 to FeOx by an increase in temperature, altering the work function of FeOx and allowing to cycle oxygen from the breaking of CO2. Through the Electrochemical Promotion of Catalysis (EPOC) phenomenon the catalytic activity can be enhanced by altering the binding energy of the reactant and intermediate species on the catalytic surface[4]. The MSI and EPOC phenomena have been shown to be functionally equivalent in terms of the change in work function. The difference between them is that in EPOC the movement of ions can be controlled through the application of an electrical current or potential difference, while the MSI effect is controlled by a thermal input. EPOC entails the use of solid electrolytes, for instance yttria-stabilized zirconia (YSZ) and barium zirconate yttrium-doped (BZY) which are oxygen and proton conductors, respectively. The catalyst-working electrodes (i.e. FeOx nanowires) are deposited on one side of the electrolyte and on the opposite side, inert gold counter and reference electrodes. Through the application of a potential difference between the electrodes, promoting species migrate through the three-phase (solid-gas-catalyst) boundary in order to interact with the exposed-catalyst surface. In the case of BZY, when a potential difference is applied between the counter and working electrode, H+ are removed from the surface through the three-phase boundary (tpb) towards BZY, referred to as positive polarization. When the polarization is reversed from the working to counter electrode, H+ migrate from BZY through the tpb towards the catalytic surface. Utilizing YSZ, results in the opposite migration with O2- ions. Regardless of the type of solid electrolyte used the catalyst is oxidized under positive polarization and reduced under negative polarization. The use of the Co3O4 semiconductor allows to combine both the MSI and EPOC effect at 350°C, by finely dispersing the Fe nanowires on Co3O4 to expose active sites and lowering the rate of sintering while being conductive to close the circuit[5]. As opposed to using other supports that do not display fully conductive properties, this approach provides an electronic path for the promoters to follow. Results have shown the working-catalyst FeOx/Co3O4 on YSZ and BZY to be highly selective to CO formation under oxidizing (3CO2:H2) and reducing (CO2:7H2) conditions, with a superior activity experienced under rich reducing conditions. Furthermore, alteration in work function from the EPOC effect, has led to a promotional response for both YSZ and BZY. Combining the MSI and EPOC effect allows for high RWGS activity, establishing a promising solution in utilizing CO2 as a resource while using transition metals. Additionally, the EPOC effect will be elucidated through Fourier-Transform Infrared (FTIR) spectroscopy to provide insight on the promoting mechanism occurring during polarization. 1. Porosoff, M. D., Yan, B. & Chen, J. G. Catalytic reduction of CO2 by H2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities. Energy Environ. Sci. 2, 303 (2015).1. Baranova, E. A., Bock, C., Ilin, D., Wang, D. & MacDougall, B. Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts. Surf. Sci. 600, 3502–3511 (2006).2. Panaritis, C., Edake, M., Couillard, M., Einakchi, R. & Baranova, E. A. Insight towards the role of ceria-based supports for reverse water gas shift reaction over RuFe nanoparticles. J. CO2 Util. 26, 350–358 (2018).3. Vayenas, C. G., Bebelis, S., Pliangos, C., Brosda, S. & Tsiplakides, D. Electrochemical Activation of Catalysis. (Springer US, 2001).4. Zagoraios, D. et al. Electrochemical promotion of methane oxidation over nanodispersed Pd/Co3O4 catalysts. Catal. Today (2019). doi:10.1016/j.cattod.2019.02.030

Catalyst Support Based on Oxygen-Deficient Titanium Suboxide Nanosheets with Pt Nanoparticles for Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cell Application

Developing stable nanocatalysts with high activity for oxygen reduction reaction (ORR) remains a great challenge in the field of clean energy. As one of the most important means of electrochemical energy conversion, proton-exchange membrane fuel cells (PEMFCs) have attracted much attention in the scientific and industrial communities [1]. There has been increasing interest in the development of advanced electrode materials for the next generation of high-performance, durable PEMFCs. Importantly, the practical use of conventional carbon supported platinum (Pt) catalyst (i.e., Pt/C) materials is limited by their low electrochemical oxidation resistance and the consequent structural collapse of the carbon-based support material in electrodes, especially under dynamic operating conditions [2,3]. As such, there are still some limitations to the performance of PEMFCs with these carbon-based hybrid electrodes, and further improvement or optimization of their electrochemical performance remains challenging. Additionally, the electronic paths in these surfaces functionalized carbon supports are not effectively shortened, because electrons move less freely between them, via direct contact or by jumping from one particle to another as the conductive carbon particles are passivated [4]. Therefore, the development of conductive and corrosion-resistant non-carbon nanostructured support materials for catalysis, to replace carbon black particle aggregates, is the ultimate route to eliminating electrochemical instability [5]. Herein, we developed two-dimensional oxygen-deficient Titania nanosheets (TiO2-x NSs) as electrocatalyst support by simple hydrothermal reaction followed by NaBH4 reduction in ambient atmosphere. Electrochemical accelerated degradation tests (ADTs) and post-test elemental analysis revealed that the higher surface area and oxygen deficiency play a key role in the high-performance corrosion-resistant TiO2-x NSs electrocatalyst supports, as they serve as a means for improving electrical conductivity. The density of states of the valence band (VB) for TiO2-x NSs was measured by X-ray photoelectron spectroscopy (XPS), and exhibited a remarkable band gap narrowing (~ 2.7 eV) based on the introduced surface defect (oxygen vacancy). After the deposition of Pt nanoparticles (NPs), the TiO2-x NS catalysts exhibited both higher electrocatalytic activity and outstanding electrochemical stability compared to commercial Pt/C. From the cyclic voltammogramms, it was observed that the Pt-TiO2-x NSs displayed positive shift of an oxidation wave assigned to the adsorption of oxygenated species (e.g., OHad, at 0.7 - 0.9 V) compared to Pt/C. These observations suggest that the surface of catalyst is less oxophilic and has weaker binding to the oxygenated species than the surface of pure Pt, which is desired for lowering the kinetic barrier of the ORR. The calculated Tafel slope was 68 mVs-1 at low current density region, indicating that the transfer of the first electron on the catalyst is the rate determining step for the adsorption of intermediates. The mass activity (MA) of the catalyst is 314 Agpt -1, which is 1.5 times higher than that of Pt/C. The enhanced activity for ORR of Pt-TiO2-x NSs was attributable to the strong metal-support interaction (SMSI) effect. Due to the spillover effect, charge transfer occurred from the TiO2-x NSs to the Pt NPs and caused the electron density of the Pt NPs to increase. Accordingly, the obtained catalyst delivers a high power density of 958 mWcm-2 in H2-O2 PEMFC at 80 °C in ambient pressure as cathode. Moreover, no decay was observed during continuous operation at 1.5 Acm-2 for 100 h from the projected catalyst support based fuel cell. Benefiting from the unique structural functionality, interaction and electronic effects, the Pt-TiO2-x NSs displayed a negligible performance deterioration overlong-term cycling, demonstrating cell performance comparable to that of state-of-the-art commercial Pt/C during practical PEMFC operation. This strategy offers a new concept for designing an ultra-low Pt loading yet highly active and durable catalytic support for fuel cell applications and beyond. ACKNOWLEDGMENTS We acknowledge the financial support from the (Grants in Aid for scientific research (KAKENHI)) Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) under the ‘Multifunctional durable nanostructured redox electrocatalysts on conducting titanium oxide support’ project (Project Number: 18F18372). Keerti M. Naik is thankful to the Japan Society for the Promotion of Sciences for a JSPS Postdoctoral Fellowship (Standard).

Insights into formation of Pt species in Pt/CeO2 catalysts: Effect of treatment conditions and metal-support interaction

The features of the formation of Pt species on the CeO2 surface from adsorbed [PtCl6-yOy] complexes in Pt/CeO2 catalysts depending on the Pt content (0.5, 1.0 and 2.0 wt.%) and treatment conditions (direct Pt precursor reduction, oxidative and reductive treatments) are studied by XRD, CO pulse chemisorption, H2-TPR, UV–vis DRS, and Raman spectroscopy. The temperature of oxidative decomposition of the Pt precursor is shown to be the key factor that defines the state and size of the Pt species formed. High pretreatment temperature (500 °C) provides Pt incorporation into ceria lattice and yields smaller Pt particles after reduction providing strong Pt–CeO2 interaction, while the reduction of the samples dried at 120 °C results in the pronounced agglomeration of the formed Pt species to yield Pt particles weakly bonded with the ceria.

Lattice distorted MnCo oxide materials as efficient catalysts for transfer hydrogenation of levulinic acid using formic acid as H-donor

Catalytic transfer hydrogenation of levulinic acid using H-donors represents one of the most promising routes to replace conventional hydrogenation processes using fossil-derived H2. Current studies on catalyst design are focused on the effects of metal composition and metal-support interaction on tandem H2 generation and hydrogenation. However, the influence of lattice-mismatch induced structural distortion on catalytic CH and CO bond cleavage is largely unexplored in this area. We proposed unique MnCo-based oxide catalysts for transfer hydrogenation of levulinic acid to γ-valerolactone using formic acid as H-donor. The key finding is that, lattice distortion of MnCo oxides induces electronically coupled MnCoO3 phase at MnOx-CoOx interface as intrinsically active site for transfer hydrogenation. Catalyst characterization by XRD, XPS, and TEM techniques were interpreted to further demonstrate the synergism of MnCo-based catalysts for tandem hydrogenation reactions. This work will provide insights into the development of structurally distorted inexpensive metal oxide catalysts for transfer hydrogenation technologies.

Restructuring effects of the chemical environment in metal nanocatalysis and single-atom catalysis

Metal-based heterogeneous catalysts mostly consist of supported nanoparticles of a few nanometers in size, since these objects provide a good compromise between exposed active surface area and structural stability. However, far from being static, heterogeneous catalysts constantly evolve under reaction conditions, thereby creating and removing surface sites in response to their gaseous or liquid reactive environment. Modern ex situ and in situ investigations have shown that nanocatalysts at work can face a number of deep restructuring phenomena, such as morphological change, compound formation, segregation, leaching, as well as redispersion and other metal-support interaction effects. Recently emerging single-atom catalysts are – like subnanometric clusters – especially sensitive to their chemical environment. Using examples from the recent literature with a particular emphasis on operando characterization studies, this article reviews the main dynamic effects induced by the reaction medium on nanocatalysts (including nanoalloy catalysts) and single-atom catalysts.

Enhancing activity and durability of Pd nanoparticle electrocatalyst by ceria undercoating on carbon support

Pd/C catalysts consisted of Pd nanoparticles (NPs) on carbon support are an important electrocatalyst in fuel cells operating on small molecules such as formic acid, methanol, and ethanol. Enhancing the performance and durability of Pd/C catalyst is an urgent issue for the commercialization of such fuel cells. Towards these ends, in this work, we report a facile sonochemical method to form a novel Pd/CeO2/C catalyst with a CeO2 undercoating layer between Pd NPs and carbon support. The CeO2 undercoating layer is composed of ~6 nm sized CeO2−x (x ~ 0.17) NPs densely covering the carbon surface. The Pd NPs in Pd/CeO2/C catalyst are formed on top of the CeO2 NPs. Spectroscopic and electrochemical analysis data indicate the presence of strong metal-support interaction (SMSI) effect between Pd and CeO2. Formic acid oxidation reaction (FAOR), studied as an exemplary reaction of electrocatalysis on Pd/CeO2/C catalyst, is enhanced from that of Pd/C catalyst by 2.4 times for specific activity and 4.8 times for mass activity. Pd/CeO2/C catalyst shows ~70% of retention of mass activity after 1000 cycles of FAO reaction, much higher than ~29% of Pd/C.

Metal-support interaction enhanced electrochemical reduction of CO2 to formate between graphene and Bi nanoparticles

Metal nanoparticles stabilized on a support material have been explored extensively to boost heterogeneous catalysis. Herein, the effect of metal-support interaction between bismuth (Bi) nanoparticles and reduced graphene oxide nanosheets (Gr) on the electroreduction of CO2 towards value-added formate is explored. The obtained Bi/Gr hybrid catalysts exhibit a superior catalytic activity towards electrochemical reduction of CO2, which gives the maximum faradic efficiency of 92.1 % at -0.97 V (vs. RHE) for formate generation. Particularly, the hydride shows an enhancement to the catalysts of bare Bi and physical mixture of Bi and Gr, with a high current density of 28.1 mA∙cm−2 and production rate of 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE) for formate generation. The electrochemical analysis reveals that the metal-support interactions substantially boost CO2 electroreduction activity through modification the electronic structure and improving interfacial electron transfer between Bi and Gr. This work not only deepens an understanding of metal-support interaction effect but also sheds light on the design of high-efficiency catalysts toward CO2 electroreduction by virtue of the interactions between active metals and carbon-like support.

Promotion effect of strong metal-support interaction to thermocatalytic, photocatalytic, and photothermocatalytic oxidation of toluene on Pt/SrTiO3

The importance of strong metal-support interaction (SMSI) in reducible oxide supported noble metal nanoparticles (NP) has been recognized in many thermocatalytic systems but rarely explored in photocatalytic and photothermocatalytic systems. Herein, the promotion effect of SMSI in strontium titanate (STO) supported Pt NP for thermocatalytic, photocatalytic, and photothermocatalytic oxidation (TCO, PCO and PTO) of toluene is reported. SMSI in Pt/STO is achieved through calcination in air (Air-Pt/STO), reduction in H2 atmosphere (H2–Pt/STO), wet reduction in HCHO solution (HCHO–Pt/STO) or NaBH4 solutions (NaBH4–Pt/STO), resulting in the formation of chemisorbed oxygen and negatively charged Pt NP and promoting oxygen activation in TCO and surface plasmon resonance effects of Pt NP in visible-light-induced PCO and PTO. Both TCO and PCO activities go along with the degree of SMSI as Air-Pt/STO > H2–Pt/STO > HCHO–Pt/STO > NaBH4–Pt/STO. Under both visible-light illuminating and thermal environment at 150 °C, the PTO toluene degradation efficiency of Air-Pt/STO is further improved with a factor of 32 times or 9 times than the single PCO or TCO process. The unique synergistic photothermocatalytic oxidation performance of Air-Pt/STO is ascribed to the function of Pt NP and the effect of SMSI. Our findings provide a facile way to design multifunctional supported noble metal catalysts for efficient VOCs degradation process.

Anchoring IrPdAu Nanoparticles on NH2-SBA-15 for Fast Hydrogen Production from Formic Acid at Room Temperature.

Hydrogen (H2), a regenerable and promising energy carrier, acts as an essential role in the construction of a sustainable energy system. Formic acid (HCOOH, FA), a natural biological metabolic products and also accessible through carbon dioxide (CO2) reduction, has a great potential to serve as a prospective H2 supplier for the fuel cell. Herein, ultrafine and electron-rich IrPdAu alloy nanoparticles with a size of 1.4 nm are highly dispersed on amine-modified mesoporous SiO2 (NH2-SBA-15) and used as a highly active and selective catalyst for fast H2 production from FA. The as-synthesized IrPdAu/NH2-SBA-15 possesses superior catalytic activity and 100% H2 selectivity with initial turnover frequency values of 6316 h-1 with the additive of sodium formate (SF) and 4737 h-1 even without SF at 298 K, comparable to the most effective heterogeneous catalysts ever published. The excellent performance of IrPdAu/NH2-SBA-15 was not only ascribed to the combination of the electronic synergistic effect of trimetallic alloys and the strong metal-support interaction effect but also attributed to the amine (-NH2) alkaline groups grafted on SBA-15, which is beneficial to boost the split of the O-H bond of FA.

Sea-Island-Like Morphology of CuNi Bimetallic Nanoparticles Uniformly Anchored on Single Layer Graphene Oxide as a Highly Efficient and Noble-Metal-Free Catalyst for Cyanation of Aryl Halides

Aryl nitriles are versatile compounds that can be synthesized via transition-metal-mediated cyanation of aryl halides. Most of the supported-heterogeneous catalysts are noble-metals based and there are very limited numbers of efficient non-noble metal based catalysts demonstrated for the cyanation of aryl halides. Herein, bimetallic CuNi-oxide nanoparticles supported graphene oxide nanocatalyst (CuNi/GO-I and CuNi/GO-II) has been demonstrated as highly efficient system for the cyanation of aryl halides with K4[Fe(CN)6] as a cyanating agent. Metal-support interaction, defect ratio and synergistic effect with the bimetallic nanocatalyst were investigated. To our delight, the CuNi/GO-I system activity transformed a wide range of substrates such as aryl iodides, aryl bromides, aryl chlorides and heteroaryl compounds (Yields: 95–71%, TON/TOF: 50–38/2 h−1). Moreover, enhanced catalytic performance of CuNi/GO-I and CuNi/GO-II in reduction of 4-nitropehnol with NaBH4 was also confirmed (kapp = 18.2 × 10−3 s−1 with 0.1 mg of CuNi/GO-I). Possible mechanism has been proposed for the CuNi/GO-I catalyzed cyanation and reduction reactions. Reusability, heterogeneity and stability of the CuNi/GO-I are also found to be good.

Effect of spinel inversion and metal-support interaction on the site activity of Mg-Al-Ox supported Co catalyst for CO2 reforming of CH4

The active metal–support interaction, as well as spinel inversion was studied for site formation, properties, activity and site resistance to carbon deposition in dry reforming of methane (DRM) using Al-Ox and Mg-Al-Ox supported Ni and Co monometallic catalysts. A change in support from Al-Ox to Mg-Al-Ox led to transformation of hysteresis loop from H2 to H4 as revealed by the N2 adsorption results, while additional MgO phase was observed from the XRD results of the catalysts. Phase quantification of the XRD showed a reduction from 100% to 45% spinel with the introduction of Mg in the support. Al and Mg K-edge XANES results revealed changes in the co-ordination number (CN) of Mg and Al inside the support, leading to spinel inversion, which ultimately affected the distribution of Ni and Co, as well as site formation on the support system. STEM EDX revealed different interaction/distribution of active metals on the support system. Co showed a uniform distribution, while Ni showed a heterogeneous distribution in addition to the isolated NiO formed on the surface of the support. The K-edge XANES results showed that more Ni sites were generated than Co sites during reduction, but Co sites showed better conversion rate for CO2, CH4, in DRM, and resistance to deactivation, which was also confirmed by the calculated TOF. This improved performance of Co sites was attributed to the better basicity per active site generated from its interaction with MgO (from the support) as compared to the Ni sites.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites.

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

Engineering stable Pt nanoparticles and oxygen vacancies on defective TiO2 via introducing strong electronic metal-support interaction for efficient CO2 photoreduction

This work for the first time reports the promoting effect of strong electronic metal-support interaction (EMSI) in Pt/TiO2-VO (VO: oxygen vacancy) for gas-phase CO2 photoreduction. A novel in-situ surface hydrogenation was developed to prepare hydrogenated Pt/TiO2-VO in a continuous, high throughput diffusion flame aerosol reactor. The combined results of various characterization techniques confirmed the presence of EMSI between Pt and defective TiO2-VO resulted in the enhanced electronic density of Pt nanoparticles. Both the modulated electronic structure of Pt and surface oxygen vacancies simultaneously promoted the activation of surface adsorbed carbon intermediates and facilitated the separation of photogenerated charges, eventually boosting the photocatalytic activity of Pt/TiO2-VO. The optimized Pt/TiO2-VO demonstrated a high quantum yield of 1.49% with high CH4 selectivity (81%), which rendered 5.8- and 1.2-fold enhancements over its counterparts of TiO2-VO and Pt/TiO2. More significantly, the EMSI also played a critical role in preserving the surface metallic Pt0 and oxygen vacancies, and in sustaining high activity of the Pt/TiO2-VO, whereas rapid catalytic deactivation are observed for both TiO2-VO and Pt/TiO2.

Effect of Surface Composition and Structure of the Mesoporous Ni/KIT-6 Catalyst on Catalytic Hydrodeoxygenation Performance

A series of Ni/KIT6 catalyst precursors with 25 wt.% Ni loading amount were reduced in H2 at 400, 450, 500, and 550 °C, respectively. The studied catalysts were investigated by XRD, Quasi in-situ XPS, BET, TEM, and H2-TPD/Ranalysis methods. It was found that reduction temperature is an important factor affecting the hydrodeoxygenation (HDO) performance of the studied catalysts because of the Strong Metal Support Interaction Effect (SMSI). The reduction temperature influences mainly the content of active components, crystal size, and the abilityfor adsorbing and activating H2. The developed pore structure and large specific surface area of the KIT-6 support favored the Ni dispersion. The RT450 catalyst, which was prepared in H2 atmosphere at 450 °C, has the best HDO performance. Ethyl acetate can be completely transformed and maintain 96.8% ethane selectivity and 3.2% methane selectivity at 300 °C. The calculated apparent activation energies of the prepared catalysts increased in the following order: RT550 > RT400 > RT500 > RT450.