Electrostatic Self-Assembly Synthesis of Pd/In2O3 Nanocatalysts with Improved Performance Toward CO2 Hydrogenation to Methanol.

CO2 hydrogenation to methanol has emerged as a promising strategy for achieving carbon neutrality and mitigating global warming, in which the supported Pd/In2O3 catalysts are attracting great attention due to their high selectivity. Nonetheless, conventional impregnation methods induce strong metal-support interaction (SMSI) between Pd and In2O3, which leads to the excessive reduction of In2O3 and the formation of undesirable PdIn alloy in hydrogen-rich atmospheres. Herein, we innovatively synthesized Pd/In2O3 nanocatalysts by the electrostatic self-assembly process between surface-modified composite precursors with opposite charges. And the organic ligands concurrently serve as Pd nanoparticle protective agents. The resultant Pd/In2O3 nanocatalyst demonstrates the homogeneous distribution of Pd nanoparticles with controllable sizes on In2O3 supports and the limited formation of PdIn alloy. As a result, it exhibits superior selectivity and stability compared to the counterparts synthesized by the conventional impregnation procedure. Typically, it attains a maximum methanol space-time yield of 0.54 gMeOH h-1gcat -1 (300 °C, 3.5 MPa, 21,000 mL gcat -1 h-1). Notably, the correlation characterization results reveal the significant effect of small-size, highly dispersed Pd nanoparticles in mitigating MSI. These results provide an alternative strategy for synthesizing highly efficient Pd/In2O3 catalysts and offer a new insight into the strong metal-support interaction.

Toward n-Alkane Hydroisomerization Reactions: High-Performance Pt-Al2O3/SAPO-11 Single-Atom Catalysts with Nanoscale Separated Metal-Acid Centers and Ultralow Platinum Content.

Long-chain n-alkane hydroisomerization reaction plays a vital role in petrochemical and coal chemical industries, which could produce high-quality hydrocarbon fuels and lubricant base oils for modern transportation and mechanical drive. However, minimizing precious metal usage while maintaining the catalyst performance remains a great challenge. Herein, a novel bifunctional catalyst toward n-alkane hydroisomerization reactions, Pt-Al2O3/SAPO-11 (Pt-A/S11) featuring nanoscale separated metal-acid active centers has been synthesized via a simple two-step procedure. In detail, Pt species was first loaded on the nanometer-sized alumina matrices through an incipient wetness impregnation method and then mixed with SAPO-11 molecular sieve to form the composite catalyst. Importantly, 0.015Pt-A/S11 catalyst with the ever-reported lowest Pt loading amount of 0.015 wt % exhibits an extraordinarily high isomer yield of 85.8% compared to previous published results and the traditional Pt-SAPO-11/Al2O3 (Pt-S11/A) catalyst accompanying with the direct contact between metal and acid sites (65.6%). It has been confirmed that the Pt species in 0.015Pt-A/S11 samples exist in single-atom form, leading to an excellent hydroisomerization performance. The possible reaction processes have been discussed to elucidate the exemplary catalytic performance of the synthesized Pt-A/S11 catalysts with nanoscale intimacy of metal-acid sites.

Bi-Sn Oxides for Highly Selective CO2 Electroreduction to Formate in a Wide Potential Window.

The electroreduction of CO2 into the highly value-added fuel formic acid (HCOOH) has been considered an ideal approach to convert renewable energy and mitigate environmental crisis. SnO2 electrode is one of the promising candidates to electrocatalytically convert CO2 to HCOOH, but its poor stability limits its future development and application. In this study, highly stable SnO2 /Bi2 O3 oxide catalysts are obtained by distributing SnO2 nanoparticles on the surface of Bi2 O3 sheets. The XPS spectra revealed an interfacial electronic transportation from Bi2 O3 sheets to SnO2 nanoparticles, which made SnO2 rich of electrons. The strong interfacial interaction protected the active sites of SnO2 from self-reduction in CO2 electroreduction reaction (CO2 RR), stabilizing SnO2 species in the composite catalyst even after long-term usage. Calculations based on density functional theory signified that the presence of Bi2 O3 favored the adsorption of HCOO* intermediate, improved the CO2 conversion into HCOOH on SnO2 /Bi2 O3 interface. As a result, the SnO2 /Bi2 O3 catalyst attained high performance on CO2 RR (the highest FE C 1 value of 90 % at -1.0 V vs. RHE), suppressing H2 evolution reaction (HER) at high potentials. In particular, the selectivity of HCOOH remained above 76 % in a wide potential window (from -1.0 to -1.4 V vs. RHE) and a long duration (12 h).

Highly Efficient and Selective CO2 Electro-Reduction to HCOOH on Sn Particle-Decorated Polymeric Carbon Nitride.

Electrochemical conversion of CO2 into liquid fuels by efficient and earth-abundant catalysts is of broad interest but remains a great challenge in renewable energy production and environmental remediation. Herein, a Sn particle-decorated polymeric carbon nitride (CN) electrocatalyst was successfully developed for efficient, durable, and highly selective CO2 reduction to formic acid. High-resolution X-ray photoelectron spectroscopy confirmed that the metallic Sn particles and CN matrix are bound by strong chemical interaction, rendering the composite catalyst a stable structure. More notably, the electronic structure of Sn was well tuned to be highly electron-rich due to the electron transfer from N atoms of CN to Sn atoms via metal-support interactions, which favored the adsorption and activation of CO2 molecules, promoted charge transport, and thus enhanced the electrochemical conversion of CO2 . The composite electrocatalyst demonstrated an excellent Faradaic efficiency of formic acid (FEHCOOH ) up to 96±2 % at the potential of -0.9 V vs. reversible hydrogen electrode, which remained at above 92 % during the electrochemical reaction of 10 h, indicating that the present Sn particle-decorated polymeric carbon nitride electrocatalyst is among the best in comparison with reported Sn-based electrocatalysts.

A large-surface-area TS-1 nanocatalyst: a combination of nanoscale particle sizes and hierarchical micro/mesoporous structures.

By a simple sequent process of dry-gel steam-assisted crystallization and following a top-down alkali-etching treatment, hierarchically structured TS-1 nanozeolites (nanoTS-1_D) with abundant micro/mesopores have been synthesized for the first time, and they exhibit remarkably high specific surface area of 606 m2 g-1 and pore volume of 0.86 cm3 g-1. Characterization by XRD, FTIR, UV-vis and EM confirm the exclusive incorporation of titanium species in zeolite frameworks. More importantly, compared with the microporous TS-1 nanocrystal material with identical particle sizes of 80 nm (nanoTS-1) and submicrometer-sized mesoporous TS-1 material (mesoTS-1), here the reported nanoTS-1_D catalyst shows greatly improved performance in the model reaction of 1-hexene epoxidation. 40.9% olefin conversion and 96.3% epoxide selectivity are achieved and its high stability is verified by the 6 recycling-regeneration tests.

CuO/Co(OH)2 Nanosheets: A Novel Kind of Electrocatalyst for Highly Efficient Electrochemical Oxidation of Methanol.

With the booming of non-noble-metal electrocatalysts for efficient oxygen reduction reaction under alkaline conditions, corresponding anodic catalysts for methanol oxidation are urgently needed especially for direct methanol fuel cells with alkaline membranes. Here, we report the facile synthesis of a CuO/Co(OH)2-nanosheet composite as a novel kind of high-performance electrochemical methanol oxidation reaction (MOR) catalyst. The obtained material with an optimized Cu/Co ratio shows much enhanced mass activity and area-specific activity, as well as excellent stability. The electronic structure interaction between Cu and Co, which results in the Co ion binding-energy elevation, is considered to be the origin of high MOR performance. This work promises the great potential of cobalt hydroxide as a novel kind of MOR catalyst and may arouse much interest in exploring more hydroxides as efficient nonprecious-metal electrocatalysts for MOR.

Metal-Organic Framework Nanosheet Electrocatalysts for Efficient H2 Production from Methanol Solution: Methanol-Assisted Water Splitting or Methanol Reforming?

Hydrogen (H2) is presently one of the most promising clean and renewable energy sources, but the conventional hydrogen production by electrochemical water-splitting, though of great potential and extensively studied, is seriously obstructed especially by the anodic oxygen evolution reaction because of its sluggish kinetics. Herein, we report the efficient hydrogen production from methanol solution using facile-synthesized ultrathin 2D bi-metal-organic framework nanosheets (UMOFNs) as a precious metal-free anodic catalyst. The prepared UMOFNs showed a much lowered anodic potential of 1.365 (V vs reversible hydrogen electrode) at 10 mA cm-2, which was markedly 232 mV lower than that in conventional water splitting, and moreover, the average turnover frequency reached 19.62 s-1. Benefiting from nearly 100% Faraday efficiency of H2 production on the counter graphite carbon electrodes without additional electrocatalysts, high-purity hydrogen was produced with enhanced efficiency. More importantly, the anodic electro-reaction mechanism has been evidenced experimentally: the electrocatalytic hydrogen production from the methanol solution is a methanol-assisted water splitting, rather than a methanol-reforming process as claimed in a number of literature studies, in which methanol is oxidized as a sacrificing agent in place of water oxidization in pure water.

Fabrication of a mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ perovskite as a low-cost and efficient catalyst for oxygen reduction.

A precious metal-free cathode catalyst, mesoporous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (m-BSCF), with a well crystallized perovskite framework and a porous structure (pore size of ∼10 nm) has been synthesized by a one-step co-nanocasting method. The obtained mesoporous perovskite m-BSCF demonstrated a much higher oxygen reduction reaction catalytic activity than its macroporous (CS-BSCF of ∼5 µm pore size) and nonporous counterparts (SG-BSCF). The mesoporous structure and oxygen vacancies endowed the obtained perovskite oxide m-BSCF with an approximate 4e- pathway for the ORR comparable to the benchmark 20 wt% Pt/C and a stable electro-catalytic activity with 91% current density being retained after 5000 cycles, and excellent methanol tolerance. The redox couples Co4+/Co3+ and Fe3+/Fe2+ are proposed to accelerate the ORR on active species, i.e., MOOH (M = Co, Fe) groups produced by the substitution species of Co and Fe in the B-site of perovskite m-BSCF, and in the meantime oxygen vacancies generated by the redox couples play a key role in activating the oxygen molecules.

Sodium carbonate-assisted synthesis of hierarchically porous single-crystalline nanosized zeolites.

Hierarchically porous single-crystalline nanosized zeolites as heterogeneous catalysts show great potential in fine chemistry because they offer more rich hierarchically porous channels for the mass transfer and molecular diffusion. However, the synthesis of hierarchically porous nanosized zeolites generally requires the assistance of templates acting as the mesoporogens, which limits its popularity. Herein, we report a one-pot and template-free synthesis of hierarchically porous single-crystalline nanosized zeolite beta only by introducing sodium carbonate in precursor solution. The resulted sample features the extraordinary properties, including the uniform nanocrystal (200-300nm), high pore volume (0.65cm3g-1) and the hierarchical pore-size distribution (e.g., 2-8 and 90-150nm). After slicing processing, it is interestingly found that a large number of interconnected mesopores penetrate throughout whole material, which enables the hierarchically porous nanosized zeolite beta remarkably superior catalytic activity than the conventional zeolite beta in condensation of benzaldehyde with ethanol at room temperature. More importantly, this one-pot sodium carbonate-assisted synthetic strategy is highly versatile, which has also been successfully developed to synthesize hierarchically porous nanosized single-crystalline zeolites ZSM-5 and TS.

Manganese Oxide Nanorod-Decorated Mesoporous ZSM-5 Composite as a Precious-Metal-Free Electrode Catalyst for Oxygen Reduction.

A precious-metal-free cathode catalyst, MnO2 nanorod-decorated mesoporous ZSM-5 zeolite nanocomposite (MnO2 / m-ZSM-5), has been successfully synthesized by a hydrothermal and electrostatic interaction approach for efficient electrochemical catalysis of the oxygen reduction reaction (ORR). The active MnOOH species, that is, Mn(4+) /Mn(3+) redox couple and Brønsted acid sites on the mesoporous ZSM-5 matrix facilitate an approximately 4 e(-) process for the catalysis of the ORR comparable to commercial 20 wt % Pt/C. Stable electrocatalytic activity with 90 % current retention after 5000 cycles, and more importantly, excellent methanol tolerance is observed. Synergetic catalytic effects between the MnO2 nanorods and the mesoporous ZSM-5 matrix are proposed to account for the high electrochemical catalytic performance.

On the Mesoporogen-Free Synthesis of Single-Crystalline Hierarchically Structured ZSM-5 Zeolites in a Quasi-Solid-State System.

Hierarchically structured zeolites (HSZs) have gained much academic and industrial interest owing to their multiscale pore structures and consequent excellent performances in varied chemical processes. Although a number of synthetic strategies have been developed in recent years, the scalable production of HSZs single crystals with penetrating and three-dimensionally (3-D) interconnected mesopore systems but without using a mesoscale template is still a great challenge. Herein, based on a steam-assisted crystallization (SAC) method, we report a facile and scalable strategy for the synthesis of single-crystalline ZSM-5 HSZs by using only a small amount of micropore-structure-directing agents (i.e., tetrapropylammonium hydroxide). The synthesized materials exhibited high crystallinity, a large specific surface area of 468 m(2) g(-1) , and a pore volume of 0.43 cm(3) g(-1) without sacrificing the microporosity (≈0.11 cm(3) g(-1) ) in a product batch up to 11.7 g. Further, a kinetically controlled nucleation-growth mechanism is proposed for the successful synthesis of single-crystalline ZSM-5 HSZs with this novel process. As expected, compared with the conventional microporous ZSM-5 and amorphous mesoporous Al-MCM-41 counterparts, the synthesized HSZs exhibited significantly enhanced activity and stability and prolonged lifetime in model reactions, especially when bulky molecules were involved.

Mesoporogen-Free Synthesis of Hierarchically Structured Zeolites with Variable Si/Al Ratios via a Steam-Assisted Crystallization Process.

In the absence of additional mesoporous template, hierarchically structured zeolites (HSZs) with variable Si/Al ratios (30-150) have been successfully synthesized via a newly developed steam-assisted crystallization process. The synthesized materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, solid-state nuclear magnetic resonance, and ammonia temperature-programmed desorption. All these results prove that the synthesized materials feature high crystallinity (microporous framework) and auxiliary mesoporous structure. In the model reactions of isopropylbenzene and 1,3,5-triisopropylbenzene cracking, compared to purely microporous ZSM-5 counterparts, here synthesized HSZs exhibited markedly enhanced catalytic performances resulting from their enlarged external surface area and shortened diffusion length in the microporous system.

Mesostructured amorphous manganese oxides: facile synthesis and highly durable elimination of low-concentration NO at room temperature in air.

At a high space velocity of 120 000 mL g(-1) h(-1) and a relative humidity of 50-90%, 98% removal of 10 ppm NO has been achieved for over 237 h and no sign of deactivation was observed with mesostructured amorphous manganese oxides (AMO), due to the prevention of the catalyst active sites from deactivation.

One-step hydrothermal synthesis of nitrogen-doped carbon nanotubes as an efficient electrocatalyst for oxygen reduction reactions.

A high amount of heteroatom doping in carbon, although favorable for enhanced density of catalytically active sites, may lead to substantially decreased electroconductivity, which is necessary for the electrochemical oxygen reduction reaction. Herein, a relatively low amount of nitrogen was successfully doped into carbon nanotubes (CNTs) by a hydrothermal approach in one step, and the synthesized nitrogen-doped CNT (CNT-N) materials retained most of the original, excellent characteristics, such as the graphitic structure, tubular morphology, and high surface area, of CNTs. The resultant CNT-N materials, although containing a relatively low amount of nitrogen doping, exhibited high electrocatalytic ORR activity, comparable to that of 20 wt% Pt/C; long durability; and, more importantly, largely inhibited methanol crossover effect.

Mesostructured platinum-free anode and carbon-free cathode catalysts for durable proton exchange membrane fuel cells.

As one of the most important clean energy sources, proton exchange membrane fuel cells (PEMFCs) have been a topic of extensive research focus for decades. Unfortunately, several critical technique obstacles, such as the high cost of platinum electrode catalysts, performance degradation due to the CO poisoning of the platinum anode, and carbon corrosion by oxygen in the cathode, have greatly impeded its commercial development. A prototype of a single PEMFC catalyzed by a mesostructured platinum-free WO3/C anode and a mesostructured carbon-free Pt/WC cathode catalysts is reported herein. The prototype cell exhibited 93% power output of a standard PEMFC using commercial Pt/C catalysts at 50 and 70 °C, and more importantly, CO poisoning-free and carbon corrosion-resistant characters of the anode and cathode, respectively. Consequently, the prototype cell demonstrated considerably enhanced cell operation durability. The mesostructured electrode catalysts are therefore highly promising in the future development and application of PEMFCs.

One-step synthesis of sulfur doped graphene foam for oxygen reduction reactions.

Sulfur doped graphene foam has been successfully synthesized by a simple solve-thermal method, which exhibited a much enhanced oxygen reduction reaction (ORR) catalytic activity as well as an especially high electrochemical stability, and would be a promising non-metal cathode catalyst for the ORR.

KF-loaded mesoporous Mg-Fe bi-metal oxides: high performance transesterification catalysts for biodiesel production.

Using newly developed mesoporous Mg-Fe bi-metal oxides as supports, a novel kind of high performance transesterification catalysts for biodiesel production has been synthesized. More importantly, the impregnation solvent was for the first time found to substantially affect the structures and catalytic performances of the resultant transesterification catalysts.

Colloidal HPMO nanoparticles: silica-etching chemistry tailoring, topological transformation, and nano-biomedical applications.

Hybridization produces the better: Colloidal hollow periodic mesoporous organosilica nanoparticles (HPMO NPs) with tunable compositions and highly hybridized nanostructures are successfully synthesized by a simple, easily scale-up but versatile silica-etching chemistry (alkaline or HF etching) for their applications in nano-fabrication and nano-medicine.

An in situ carbonization-replication method to synthesize mesostructured WO3/C composite as nonprecious-metal anode catalyst in PEMFC.

A meostructured WO(3)/C composite with crystalline framework and high electric conductivity has been synthesized by a new in situ carbonization-replication route using the block copolymer (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) present in situ in the pore channels of mesoporous silica template as carbon source. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetry differential thermal analysis, and N(2) adsorption techniques were adopted for the structural characterization. Cyclic voltammetry, chronoamperometry, and single-cell test for hydrogen electrochemical oxidation were adopted to characterize the electrochemical activities of the mesoporous WO(3)/C composite. The carbon content and consequent electric conductivity of these high-surface-area (108-130 m(2) g(-1)) mesostructured WO(3)/C composite materials can be tuned by variation of the duration of heat treatment, and the composites exhibited high and stable electrochemical catalytic activity. The single-cell test results indicated that the mesostructured WO(3)/C composites showed clear electrochemical catalytic activity toward hydrogen oxidation at 25 °C, which makes them potential non-precious-metal anode catalysts in proton exchange membrane fuel cell.

An in situ carbonaceous mesoporous template for the synthesis of hierarchical ZSM-5 zeolites by one-pot steam-assisted crystallization.

Blackened catalyst: Zeolites with large external surface area and mesopore volume were synthesized by a one-pot templating strategy, in which the crystallization proceeded concurrently with in situ carbonization templating to produce a mesoporous structure. The hierarchical materials exhibited superior catalytic performance over conventional zeolites in Friedel-Crafts acylation of anisole.