Enhancement Of Catalytic Performance Research Articles

Reaction Environment Modification in Covalent Organic Frameworks for Catalytic Performance Enhancement.

Herein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer-sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5-hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1-methyl-2-pyrrolidinone and ionic liquid.

Reaction Environment Modification in Covalent Organic Frameworks for Catalytic Performance Enhancement

AbstractHerein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer‐sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5‐hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1‐methyl‐2‐pyrrolidinone and ionic liquid.

Au-BINOL Hybrid Nanocatalysts: Insights into the Structure-Based Enhancement of Catalytic and Photocatalytic Performance

Advances in new systems of organic–inorganic hybrid nanocomposites are less prevalent, owing to a lack of facile strategies for precise control of their structures, compositions, and, hence, their properties. In this work, Au-BINOL hybrid nanocomposites with eccentric and concentric nanostructures were produced. The hybrid nanocomposites containing two distinct moieties of inorganic Au nanocrystals and organic BINOL nanospheres were applied to the catalytic hydrogenation of 4-nitrophenol with NaBH4 in the aqueous phase with and without the illumination of visible light. Here, we demonstrate that the existence of Au–BINOL interfaces offers benefits to their performance. The eccentric nanostructures made with CTAC show the superior activity from large Au–BINOL interfaces formed between the BINOL nanospheres and the faces of Au nanoplates. They further exhibit a high Au localized surface plasmon resonance (LSPR)-enhancement effect on the photoreduction of 4-nitrophenol, which is attributed to the strong LSPR...

Enhancement of catalytic performance of porous membrane reactor with Ni catalyst for combined steam and carbon dioxide reforming of methane reaction

The reaction characteristics of combined steam and carbon dioxide reforming of methane (CSCRM) were examined using a Ni/Al2O3 catalyst for the gas-to-liquid (GTL) process. The concentrations of the products (outlet H2 and CO) were affected by the concentrations of the reactants (CH4, H2O, and CO2) in the feed, which also influenced the catalyst activity based on the quantity of carbon deposited on the catalyst surface. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) showed that the quantity rather than the type of carbon deposited differed under each reaction condition. It was found that the Ni/Al2O3 catalyst combined with porous membrane reactor can efficiently enhance the catalytic activity, where the methane conversion reached 96% with outlet H2/CO ratio of 2.1 at 800 °C (CH4/H2O/CO2 = 1/0.75/0.25) and gas hourly space velocity of 15,600 h−1 under 2 atm.

Pyridinic-N Protected Synthesis of 3D Nitrogen-Doped Porous Carbon with Increased Mesoporous Defects for Oxygen Reduction.

Nitrogen (N)-doped carbons are potential nonprecious metal catalysts to replace Pt for the oxygen reduction reaction (ORR). Pyridinic-N-C is believed to be the most active N group for catalyzing ORR. In this work, using zinc phthalocyanine as a precursor effectively overcomes the serious loss of pyridinic-N, which is commonly regarded as the biggest obstacle to catalytic performance enhancement upon adopting a second pyrolysis process, for the preparation of a 3D porous N-doped carbon framework (NDCF). The results show only ≈14% loss in pyridinic-N proportion in the Zn-containing sample during the second pyrolysis process. In comparison, a loss of ≈72% pyridinic-N occurs for the non-Zn counterpart. The high pyridinic-N proportion, the porous carbon framework produced upon NaCl removal, and the increased mesoporous defects in the second pyrolysis process make the as-prepared catalyst an excellent electrocatalyst for ORR, exhibiting a half-wave potential (E1/2 = 0.88 V) up to 33 mV superior to state-of-the-art Pt/C and high four-electron selectivity (n > 3.83) in alkaline solution, which is among the best ORR activities reported for N-doped carbon catalysts. Furthermore, only ≈18 mV degradation in E1/2 occurs after an 8000 cycles' accelerating stability test, manifesting the outstanding stability of the as-prepared catalyst.

Ionic liquid green synthesis of CeO2 nanorods and nano-cubes: Investigation of the shape dependent on catalytic performance

A new facile and scalable approach for utilizing basic ionic liquid, 1-butyl-3-methylimidazolium hydroxide ([BMIM]+OH−) for the fabrication of different shapes of ceria nanostructures was adopted. The features of the fabricated ceria and their corresponding gold nanocatalysts were characterized by employing ICP, HRTEM, XRD, XPS, BET and UV–vis spectroscopy. Catalytic performance of CeO2 and its dependence on shape was studied in the oxidation of CO and olefins epoxidation. The ratio between the ionic liquid and cerium precursor is one of the valuable factors used to monitor the growth of the particles. The catalytic performance of ceria was found to be dependent on the morphology of the catalysts. The catalytic performance of CeO2 in the form of nanorod-shapes is better than that of nanocubes and bulk. The deposition of gold nanoparticles on different shaped CeO2 much enhanced their catalytic performance. This enhancement in catalytic performance was, however, more significant in the case of rod-shaped ceria.

Design of Pd-based pseudo-binary alloy catalysts for highly active and selective NO reduction.

The development of Pd-based alloy catalysts for highly active and selective reduction of NO by CO was investigated. A survey of Pd-based bimetallic catalysts (PdM/Al2O3: M = Cu, In, Pb, Sn, and Zn) revealed that the PdIn/Al2O3 catalyst displayed excellent N2 selectivity even at low temperatures (100% at 200 °C). The catalytic activity of PdIn was further improved by substituting a part of In with Cu, where a Pd(In1-x Cu x ) pseudo-binary alloy structure was formed. The optimized catalyst, namely, Pd(In0.33Cu0.67)/Al2O3, facilitated the complete conversion of NO to N2 (100% yield) even at 200 °C and higher, which has never been achieved using metallic catalysts. The formation of the pseudo-binary alloy structure was confirmed by the combination of HAADF-STEM-EDS, EXAFS, and CO-FT-IR analyses. A detailed mechanistic study based on kinetic analysis, operando XAFS, and DFT calculations revealed the roles of In and Cu in the significant enhancement of catalytic performance: (1) N2O adsorption and decomposition (N2O → N2 + O) were drastically enhanced by In, thus resulting in high N2 selectivity; (2) CO oxidation was promoted by In, thus leading to enhanced low-temperature activity; and (3) Cu substitution improved NO adsorption and dissociation (NO → N + O), thus resulting in the promotion of high-temperature activity.

Synergetic promotional effect of oxygen vacancy-rich ultrathin TiO2 and photochemical induced highly dispersed Pt for photoreduction of CO2 with H2O

The ultrathin TiO2 nanosheets (TiO2-U) with abundant defects were successfully fabricated as substrates to support well-dispersed Pt nanoparticles with low metal loading by photochemical route (P), with impregnated Pt/TiO2-U, Pt/TiO2-bulk and photoreduced Pt/TiO2-bulk as control samples, to focus on studying the inductive effect of oxygen vacancy-rich ultrathin TiO2 on highly dispersed Pt nanoparticles, and their synergetic promotional effect for CO2 photoreduction. As expected, P-Pt/TiO2-U exhibited excellent photocatalytic efficiency for the selective conversion of CO2 into CH4 and CO. The ultrathin TiO2 nanosheets with a large number of low coordinative sites and ultralarge surface area promoted the rate of electron-transfer. The ultrafine Pt nanoparticles induced by photochemical strategy facilitated the efficient separation of electron–hole pairs. Furthermore, the synergy of metal and support improved the adsorption ability of CO2. These three factors were considered to drive jointly the enhancement of catalytic performance in this system. This work offers deep insights for the design of highly efficient catalysts with coordinatively unsaturated sites for CO2 photoconversion in the presence of H2O.

Gravity-driven catalytic nanofibrous membrane with microsphere and nanofiber coordinated structure for ultrafast continuous reduction of 4-nitrophenol

Silver loaded nanofibrous membrane with high catalytic performance for 4-nitrophenol under continuous gravity-driven filtration was developed in this study. A polydopamine (PDA) microsphere and nanofiber coordinated composite structure was fabricated through an in situ PDA synthesis to achieve a high catalyst loading and controllable residence time of 4-nitrophenol. The incorporated PDA microspheres played an important role for the enhancement of catalytic performance due to the increased surface area (23% increase compared with PAN and PAN-PDAs-Ag) and reduced membrane porosity. Silver loading amount and the residence time of 4-nitrophenol was increased by more than 108% (from 1.2 wt% to 2.5 wt%) and 45% (from 0.79 s to 1.15 s) when comparing with PAN-PDAc-Ag and PAN-PDAs-Ag nanofibrous membrane. The conversion rate of 4-nitrophenol in a gravity-driven filtration process was as high as 97% when PAN-PDAs-Ag nanofibrous membrane was used, which was much higher than the PAN-PDAc-Ag membrane (80%). In addition, the PAN-PDAs-Ag nanofibrous membrane exhibited excellent recycle performance, the conversion rate was maintained as high as 93% after five times of reuse. The microsphere and nanofiber coordinated structure with enhanced surface area and controllable residence time of contaminants proposed in this study might advance the real applications of electrospun nanofibrous membrane for catalytic removal of contaminants.

Graphitic carbon nitride co-modified by zinc phthalocyanine and graphene quantum dots for the efficient photocatalytic degradation of refractory contaminants

Broad solar light absorption and rapid photogenerated electron-hole pair separation are two critical factors for the efficient enhancement of catalytic performance in a g-C3N4-based photocatalytic system. This study developed a facile method to construct a ternary graphitic carbon nitride/zinc tetracarboxyphthalocyanine/graphene quantum dots (g-C3N4/ZnTcPc/GQDs) composite photocatalyst. Graphene quantum dots (GQDs) were used to modify g-C3N4/ZnTcPc through hydrothermal method, where g-C3N4/ZnTcPc was fabricated by immobilizing zinc tetracarboxyphthalocyanine (ZnTcPc) onto g-C3N4 covalently via amido bonds. The photocatalyst was characterized by transmission electron microscopy, ultraviolet-visible diffuse reflectance spectrum, and X-ray photoelectron spectroscopy. The g-C3N4/ZnTcPc/0.1GQDs composites presented an increased photocatalytic activity by using Rhodamine B, sulfaquinoxaline sodium and carbamazepine as the model pollutants under solar light irradiation. ZnTcPc bonding on the g-C3N4 broadens its visible-light spectral response, and GQDs promotes the photogenerated electron-hole-pair separation efficiency because of its efficient electrons-transfer property. Experiments confirmed that superoxide radicals, photogenerated holes and singlet oxygen are the primary active species. The photocatalytic degradation pathway of Rhodamine B, sulfaquinoxaline sodium and carbamazepine was proposed on the basis of ultra-performance liquid chromatography and high-definition mass spectrometry.

Synthesis of the Ag/Ag3PO4/diatomite composites and their enhanced photocatalytic activity driven by visible light

Herein, a novel visible-light responsive Ag/Ag3PO4/diatomite composites was successfully fabricated through a Deposition-Hydrothermal-Photoreduction method by using diatomite as the substrate. The crystal structure and morphology of the as-prepared samples were characterized by XRD, SEM, EDS and TEM. It can be found that a large number of spherical Ag/Ag3PO4 nanoparticles evenly loaded the surface of the diatomite substrate. The photocatalytic performances of the Ag/Ag3PO4/diatomite composites were evaluated by degradation RhB under visible-light irradiation (λ ≥ 420 nm). The effect of the adding amount of diatomite on the photocatalytic activity of the composite was also analyzed. The results indicated that the Ag/Ag3PO4/diatomite composites exhibit highest photocatalytic activity when the adding amount of diatomite reached 20%. The degradation rate of the Ag/Ag3PO4/diatomite-20% composites to RhB is as high as 90%, and the photoreaction kinetics constant value of the Ag/Ag3PO4/diatomite is 0.0371 which is 4.25 times higher than that of pure Ag3PO4 nanoparticles. Moreover, the mechanism of catalytic performance enhancement also has been discussed, the high photocatalytic performance of the Ag/Ag3PO4/diatomite composites can be attributed to the synergistic effect of Ag3PO4, diatomite and Ag nanoparticles. The radical trap experiments indicated that holes and O2− were served as the main active species. The Ag/Ag3PO4/diatomite composites synthesized via a facile and cost-effective route is a promising candidate in organics removal.

One-pot synthesis of Al2O3 modified mesoporous ZrO2 with excellent thermal stability and controllable crystalline phase

In this paper, a series of Al2O3 modified mesoporous ZrO2 (M-ZrAl) materials are designed and achieved through a one-pot EISA strategy. As proved by different characterizations, the introduced Al2O3 species exist as highly dispersed states, and the crystalline phase (t-ZrO2 and m-ZrO2) of M-ZrAl material could be accurately controlled through adjusting the content of Al2O3 species. Moreover, the M-ZrAl-10 material exhibits excellent textural properties (specific surface area (56 m2·g−1), pore size (8.2 nm) and pore volume (0.13 cm3·g−1)) even treated at 800 °C. The obtained materials are employed as support for MoO3/M-ZrAl solid acid catalyst, and the relationship between catalytic performance (Friedel-Crafts alkylation, acetalization and esterification) and crystalline structure of support is specially explored. The result shows that the support with t-ZrO2 phase is beneficial for the formation of acid sites and enhancement of catalytic performance for the MoO3/M-ZrAl solid acid catalyst.

Synthesis of magnetically separable MnO2/Fe3O4/silica nanofiber composite with enhanced Fenton-like catalytic activity for degradation of Acid Red 73

For the first time, the hierarchical MnO2/Fe3O4/silica nanofiber (MnO2/Fe3O4/SNF) composite was successfully fabricated by immobilization of highly dispersed Fe3O4 nanoparticles and MnO2 nanosheets on the surface of chrysotile-based silica nanofiber through layer-by-layer assembly. In the composite, the silica nanofiber was served as backbone to inhibit the self-aggregation of nano-sized catalysts and maintain the stability of the overall structure. The as-synthesized composite was employed to catalyze the degradation process of Acid red 73 (AR-73) with the assistance of peroxymonosulfate (PMS). It was found that the composite exhibited an obvious enhancement in catalytic performance in comparison to the unsupported MnO2 and Fe3O4/MnO2 nanoparticles. Besides, the composite exhibited other advantages of easy separation and good recyclability. It was proposed that the excellent catalytic activity could be attributed to the high dispersion structure of the nano-catalyst in the composite. This research also exhibited the great potential of chrysotile-derived silica nanofiber as support material for the efficient assembly of nano-sized catalyst to apply in environmental remediation.

Enhancement of catalytic performance by regulating the surface properties of Fe3O4 composites

Abstract As magnetic catalyst material, great studies have been made to improve the catalytic performance of Fe3O4 nanoparticles by changing the structure, but little attention has been paid to the relationship between the surface properties (the electronegativity, electron transport capacity) and the catalytic performance of Fe3O4 nanoparticles. Therefore, this work was devoted to the investigation of the relationship by loading Fe3O4 nanoparticles on graphene oxide(GO) grafted with N,N,N',N'-Tetrakis (2-hydroxyethy)ethylenediamine (THEED), which was denoted as TG@Fe3O4. N atoms in THEED and GO have strong electronegativity and electron mobility respectively, which greatly change the surface properties of the Fe3O4 composite. A large number of characterization methods have proved that the original structure of the produced Fe3O4 nanoparticles has not been changed, and the Zeta potential and cyclic voltammetry curves confirmed that the surface properties of Fe3O4 composite have been improved. In the Fenton degradation experiment of MB, TG@Fe3O4 can make the degradation rate of MB reach 100% in 8 min, which verified that the strong electronegativity and electron transport capacity were beneficial to the improvement of the catalytic performance of Fe3O4 composite.

Electrocatalytic Properties of Binuclear Cu(II) Fused Porphyrins for Hydrogen Evolution

Binuclear copper(II) porphyrins in which two copper(II) porphyrin macrocycles are doubly fused at the meso-beta positions are shown to be active electrocatalysts for the hydrogen evolution reaction (2H+ + 2e– → H2). Structural characterization, including use of electron paramagnetic resonance and X-ray photoelectron spectroscopies, verifies the fused species contains two copper(II) metal centers in its resting state. In comparison to the nonfused copper(II) porphyrin complex, the fused species is reduced at significantly less applied bias potentials (ΔE1/2 ∼ 570 mV for the first reduction process). Electrochemical characterization in the presence of substrate protons confirms the production of hydrogen with near-unity Faradaic efficiency, and kinetic analysis shows the catalyst achieves a maximum turnover frequency above 2 000 000 s–1. The enhancement in catalytic performance over analogous nonfused copper(II) porphyrins indicates extended macrocycles provide an advantageous structural motif and design el...

Surface Engineering of Nanostructured Energy Materials.

All nanostructures share a common feature of large surface-to-volume ratio, which makes surface engineering a vital tool for exploring their new and important applications in many different areas. Particularly, inorganic nanostructures represent a class of intriguing catalysts that can find wide uses in energy conversion, energy storage, and environmental remediation. Here, a number of surface engineering strategies, including morphology control, defect incorporation, and interface manipulation for tailoring the shape, facet, defect, interfacial property, and composition of nanostructures, aiming at controlling the chemical and physical properties such as energy bandgap and surface energy toward great enhancement in catalytic performance, are discussed.

Design of Efficient Noble Metal Free Copper‐Promoted Nickel‐Ceria‐Zirconia Nanocatalyst for Bio‐Fuel Upgrading

AbstractA new series of noble metal free bimetallic Cu−Ni supported ceria‐zirconia catalysts (Cu−Ni/CZ) has been developed with various Cu/Ni ratios by a simple co‐precipitation/impregnation method. Aqueous‐phase hydrodeoxygenation (HDO) of vanillin a typical compound of lignin‐derived bio‐oil, in promoting biomass refining was carried out to investigate catalytic performances under 25 bar of H2 pressure at 160oC. All the as‐synthesized catalysts were thoroughly characterised employing powder XRD, Raman spectroscopy, H2‐TPR, HR‐TEM, HAADF‐STEM, EDS Mapping, and XPS. It was found that 15 wt% Cu on Ni/CZ (Cu−Ni/CZ−B) nanocomposite enhanced activity significantly in comparison with other bimetallic or monometallic catalysts, exhibiting ∼98% of vanillin conversion and ∼94% of selectivity toward 2‐methoxy‐4‐methylphenol as a desired product. The Cu−Ni/CZ−B catalyst shows ∼4‐fold increase in activity compared with Cu−Ni/CeO2 and Cu−Ni/ZrO2, the mono oxide supported counterparts. The superior catalytic performance with improved stability were explained by synergistic effects at the interfaces of each species, in which electron interactions between Ni, Cu, and ceria‐zirconia support generated novel active sites. XRD and HR‐TEM revealed that Cu−Ni bimetallic phases were created on the ceria‐zirconia, which were responsible for enhancement of catalytic performance with no significant drop in catalytic activity with desired product selectivity for eleven successive catalytic cycles demonstrating the excellent stability and reproducibility of this catalyst system.

The remarkable promotion of in situ formed Pt-cobalt oxide interfacial sites on the carbonyl reduction to allylic alcohols

Pt catalysts attract increasing attention for selectively hydrogenating α,β-unsaturated aldehydes to produce allylic alcohols, thanks to their relatively satisfactory selectivity towards the reduction of CO bond over CC bond. Here, new carbon supported cobalt oxide-decorated platinum nanocatalysts for highly selective hydrogenation of cinnamaldehyde were fabricated via a facile composite precursor route. As-fabricated cobalt oxide-decorated Pt catalyst at a Co/Pt atomic ratio of 0.6 was found to exhibit an exceptional catalytic performance with an extremely high 99% yield of cinnamyl alcohol under mild reaction conditions (2 MPa H2 and 80 °C). In contrast to that of the undecorated Pt one, the intrinsic activity of the cobalt oxide-decorated Pt-based one, i.e. the turnover frequency for cinnamaldehyde conversion (4.19 s−1), was significantly increased by 9.5 times. The present catalyst system presents a particularly dramatic enhancement in catalytic performance, in comparison with other Pt-based hydrogenation catalysts previously reported. Such exceptional catalytic efficiency was probably corelated with unique geometric and electronic modifications of Pt particles by CoOx species, thereby giving rise to both the increased exposed active metal surface and the favorable electron-rich state of Pt0 species. Correspondingly, the rate of cinnamaldehyde conversion could be improved and the adsorption of the carbonyl group could be strengthened. This synergy between CoOx species and Pt sites is accounted for the observed superiority of CoOx-decorated Pt catalyst to Co-free Pt one in selective hydrogenation of carbonyl compounds.

Enhancement of Catalytic Performance of H-Clinoptilolite in Toluene Abatement from Polluted Air via Controlled Dealumination Method

AbstractIn this study, the effect of clinoptilolite dealumination on the total oxidation of toluene was reported for the first time. To avoid excess decrease of catalyst crystallinity, chemical modification of zeolite was carried out using a mild acid like oxalic acid. The catalysts were characterized by XRD, XRF, SEM, BET and TPD analyses. It was found that dealumination resulted in a significant enhancement of toluene conversion when 0.050 M acid oxalic was used for a treatment period of 2 h. Dealumination substantially changed the distribution of the concentration of acid sites of different strength and increased the surface area and porosity, so that the temperature corresponding to the maximum conversion shifts around 50 °C towards lower temperatures (in case of CLP 050). The effect of dealumination on the activity of the zeolite samples and the total oxidation of toluene was discussed in terms of Si/Al ratio, crystallinity, distribution of acid site strength and textural characteristics of the samples.

A significant enhancement of catalytic performance by adjusting catalyst wettability

固相材料的浸润性(包括亲水性、疏水性、亲油性和疏油性)已经成为设计与合成多相催化材料中必须要考虑的因素. 总结近年来的实验结果发现, 催化材料的浸润性对分子的扩散有显著影响, 适宜的浸润性与活性中心的协同是增强催化性能的关键, 这可以通过(i)有效富集反应物、(ii)快速扩散产物、(iii)促进形成反应中间体、(iv)避免副反应和(v)提高催化材料结构等因素来提升多相催化材料的活性、选择性和反应寿命, 这为设计与制备高效多相催化材料提供了新机遇.