Enhancement Of Catalytic Activity Research Articles

Efficient processing of crude oil using direct cracking at high temperatures over modified FCC catalysts

The direct cracking of Bach Ho crude oil, having API gravity of 41°, over equilibrium FCC catalyst (Ecat), modified FCC catalyst (HT-FCC) and ZSM-5 additive were studied at 620–650 °C using short-contact-time micro activity testing unit. HT-FCC catalyst was prepared by the treatment of Ecat with oxalic acid in reflux condition. This treatment largely improves the porosity while keeping the particle size of Ecat. Hence, it leads to an important enhancement in catalytic cracking activity. Due to high activity of HT-FCC catalyst, the direct cracking of crude oil can be performed at a low catalyst-to-oil ratio (C/O) which helps to decrease the yield of dry gas. At 620–650 °C, C/O of 1.5–2.5, 18–23 wt.% of light olefins, 3–6 wt.% of dry gas together with 51–59 wt.% of gasoline yields can be obtained with HT-FCC catalyst. ZSM-5 addition favors the conversion of gasoline to light olefins. Compared to the results reported in literature, the use of HT-FCC and ZSM-5 catalysts at 650 °C, low C/O of 1.5 shows promising performances: (i) much lower dry gas yield (8%), (ii) high light-olefins yield (32%) while maintaining high gasoline yield (43%), and (iii) high BTXs content in gasoline (45%).

Synergistic effect of Cu doping and NiPx/NiSey heterostructure construction for boosted water electrolysis

Heterostructure engineering and heteroatom-doping are effective strategies to develop efficient electrocatalyst for water splitting, however, the synergistic effect of these two strategies is seldom evaluated. In this work, micro-amount copper-doped nickle phosphide-selenide hetero-nanosheets electrocatalyst (Cu-NiPx/NiSey) is prepared on nickel foam by one-step phosphorus-selenization. The introduction of Cu facilitates the formation of multicomponent NiPx/NiSey heterostructures, and can also introduce a significant electronic modulation effect to produce high-valent Ni sites and NiOOH active species, benefiting for the oxygen evolution reaction (OER). The high intrinsic catalytic activity of nickle phosphide is compatible well with the high electrical conductivity of selenide, resulting in complementary enhancement of catalytic activity for Cu-NiPx/NiSey. As a result, the Cu-NiPx/NiSey electrodes exhibit extremely low overpotentials in 1 M KOH solution of 264 mV for OER at a current density of 100 mA cm−2, and 69 mV for HER at 10 mA cm−2. Importantly, when Cu-NiPx/NiSey is assembled as both electrodes, a high current density of 100 mA cm−2 can be achieved for over 60 h with only an ultra-low battery voltage of 1.71 V, exceeding most reported nickel-based bifunctional catalysts. The present work delivers a new strategy for designing and constructing effective bifunctional electrocatalysts for practical large-scale water splitting.

Constructing rose-like mesoporous SiO2@BiOCl/Bi24O31Cl10 heterojunction photocatalysts for enhanced degradation of antibiotic

Heterogeneous photocatalysis provides a sustainable pathway to solve the problems of energy shortage and environmental remediation. In this work, rose-like SiO2@BiOCl/Bi24O31Cl10 photocatalyst is composed of mesoporous SiO2, BiOCl nanosheets and Bi24O31Cl10 nanoparticles. The as-obtained photocatalysts show satisfactory photocatalytic degradation of ofloxacin (OFX) efficiency, which could remove 90% of OFX in 6 min under UV–visible light irradiation. Moreover, Rose-like SiO2@BiOCl/Bi24O31Cl10 catalysts showed good stability and recyclability, it maintained a removal efficiency of 81% in the tenth cycle. The enhancement of catalytic activity is mainly attributed to the presence of SiO2, which increases the light scattering and broadens the light absorption range. Furthermore, the synergistic effect between the SiO2, BiOCl and Bi24O31Cl10 could effectively accelerate the separation of the photo-generated carriers, which facilitate to generate reactive oxygen species, then effectively degrade the OFX. Therefore, this paper provides an important step for the rational synthesis of mesoporous SiO2 heterojunction photocatalysts for environment remediation.

Construction of a controllable and dispersed Fe3O4-based catalyst using ZIFs as a spatial support for highly catalytic degradation of aflatoxin B1

A Fe3O4-based catalyst with controllable properties and good dispersity was constructed utilizing zeolitic imidazolate frameworks (ZIFs) as a spatial support. Fe3O4 was attached onto the ZIFs surface via a facile strategy and the resulting Fe3O4/ZIFs material was applied as peroxymonosulfate catalyst for highly effective aflatoxin B1 (AFB1) degradation. The AFB1 degradation efficiency can be regulated by controlling the surface area and pore distribution of Fe3O4/ZIFs. Fe3O4/ZIFs (1:8) exhibited good catalytic ability within a wide pH range (3−8). A degradation efficiency of 97.4 % was achieved within 30 min, with 80.3 % degraded within the first 5 min, which was attributed to the ZIFs support structure, effectively improving the dispersity and mass transfer efficiency of Fe3O4. O2·− and 1O2 were the dominant active species in AFB1 degradation. Subsequently, the AFB1 degradation pathway was proposed. This study provides a promising and novel approach to the enhancement of catalytic activity for efficient AFB1 degradation.

Plasmon-promoted oxygen evolution catalysis with Ag nanocrystals loaded α-Co(OH)2 nanosheets

Exploration of low-cost and high efficiency oxygen evolution reaction (OER) electrocatalysts is very important for the large-scale industrial application of alkaline water splitting driven by electricity. The present promising cobalt-based catalysts still leave room to meet the activity requirement. Here, a composite catalyst of α-Co(OH)2/Ag was synthesized by a simple photochemical deposition route, which was designed to improve the electrocatalytic activity for OER. Moreover, a photoinduced surface plasmon on Ag particles was found to further enhance the catalytic performance under low power of laser irradiation. Loading of silver nanocrystals on α-Co(OH)2 nanosheets can decrease the overpotential towards OER for 10 mA cm−2 from 320 to 288 mV, this value can be further decreased of 45 mV under 1000 mW of laser irradiation with a wavelength of 532 nm. The derivation of the catalyst during the OER process was examined, which indicates the structural transformation from α-Co(OH)2 to CoOOH. The photoinduced surface plasmon modulates the electronic structure of cobalt sites, facilitates the formation of active cobalt species, and induces the enhancement of catalytic activity. These findings may give some hints for plasmon-induced electrocatalysis and the design of advanced electrocatalysts.

In-situ etching of stainless steel: NiFe2O4 octahedral nanoparticles for efficient electrocatalytic oxygen evolution reaction

The development of non-noble metal electrocatalysts for oxygen evolution reaction (OER) has attracted widespread attention in the field of energy. Herein, we report a facile in-situ etching method to convert commercial stainless steel felt (SSF) into NiFe 2 O 4 octahedral nanoparticles as an efficient and robust OER electrode. This preparation method of NiFe 2 O 4 is different from the conventional ones, both nickel and iron elements come from the substrate itself without extra addition of precursors, as well as NiFe 2 O 4 octahedral nanoparticles are self-grown directly on the substrate without binder. The treated SSF shows good water oxidation properties with low overpotential, small Tafel slope, and durable stability at 500 mA cm −2 for 200 h. Moreover, the effect of NaNO 3 in the etchant is studied carefully, which plays the function of removal of chromium and promoting the formation of octahedral nanoparticles, resulting in the enhancement of conductivity and catalytic activity. This study presents a new preparation method for producing NiFe 2 O 4 octahedral nanoparticles with the characteristic of low cost, simple process, wide raw material sources, and favorable OER activity, which demonstrates a good application prospect in the field of large-scale hydrogen production. • Low cost NiFe 2 O 4 octahedral nanoparticles are prepared by a facile in-situ etching of stainless steel felt. • The prepared NiFe 2 O 4 octahedral nanoparticles exhibit high catalytic activity and good long-term stability for OER. • NaNO 3 is proved to have the function of removing Cr and promoting the formation of octahedral nanoparticles.

Electrochemical post-treatment of bimetallic-ICP/RGO precursor for Z-scheme CuOx·Ag2O/RGO hetero-structure with catalytic activity enhancement for visible-light-driven photo-Fenton degradation of tetracycline

In this work, rationally designed bimetallic infinite coordination polymer (ICP) was mixed with reduced graphene oxide (RGO) to serve as precursors for the preparation of CuOx·Ag2O/RGO hetero-structure. As the growth of metal oxide nuclei within the ICP network was restricted and more surface-oxygenated species of RGO were exposed during the electrochemical post-treatment process, the CuOx·Ag2O NPs supported on RGO were evenly-distributed nanoparticles with ultra-small size (2.89 ± 0.37 nm), which exhibited excellent catalytic activity enhancement in visible-light-driven photo-Fenton degradation of the model antibiotic tetracycline (TC). Moreover, since the CuOx·Ag2O/RGO was in-situ decorated on ITO glass, recycling of the catalysts with long-term stability could be realized, even after 5 cycles, 91.4 % of TC (10 mL, 50 mg/L) could be degraded within 60 min. A series of characterization and experiment results demonstrated the improved catalytic performance of CuOx·Ag2O/RGO for photo-Fenton degradation was stemmed from the synergistic effect of the components within the catalyst, which facilitated solar energy absorption, accelerated the separation of photo-generated hole-electron pairs through Z-scheme charge transfer way, and strengthened their mechanical stability on the substrate. This newly created catalysts for photo-Fenton reaction are of great potential to achieve the practical treatment of antibiotics-contaminated wastewater.

AuPt alloy nanoparticles supported on graphitic carbon nitride: In situ synthesis and superb catalytic performance in the light-assisted hydrolytic dehydrogenation of ammonia borane

Addressed herein is the enhancement of catalytic activity of Pt-based nanocatalysts in the hydrolysis of ammonia borane (AB) via in-situ synthesis of bimetallic AuPt alloy nanoparticles (NPs) supported on graphitic carbon nitride (gCN). The presented in-situ synthesis protocol yielded gCN/AuxPt100-x (x = 0, 8, 15, 33) nanocatalysts with highly dispersed AuxPt100-x NPs having the average particle sizes varied in the range of 1.6–2.6 nm over the gCN nanosheets. The generated gCN/Pt92Au8 (600.3 mol H2 mol Pt−1 min−1) and gCN/Pt85Au15 (587.1 mol H2 mol Pt−1 min−1) nanocatalysts showed higher catalytic activity compared to gCN/Pt100 (525.7 mol H2 mol Pt−1 min−1) under white-light irradiation, attributed to the synergistic effects aroused in the AuPt alloy NPs and heterojunctions formed between gCN and AuPt alloy NPs. The detailed characterization of photophysical properties of gCN/AuxPt100-x nanocatalysts revealed that their boosted catalytic activity is attributed to the improved charge kinetics, higher light absorption, and effective electron transfer channels from gCN to the bimetallic AuPt alloy NPs. The role of photogenerated carriers in the photocatalytic AB dehydrogenation was also elucidated via scavenger studies. This study shows that gCN/AuxPt100-x nanocatalysts can be prepared in situ during the hydrolysis of AB at room temperature and the yielded nanocatalysts have a significant role in boosting the hydrogen production from the light-assisted hydrolysis of AB.

Construction of pyroelectrically-driven BiFeO3@CuBi2O4 nanofiber composite catalyst for enhanced pyrocatalytic activities under room-temperature cold and hot cycles

In this present work, a significant enhancement of pyroelectrically-driven catalytic activity is found in BiFeO3@CuBi2O4(BFO@CBO) heterostructures synthesized by electrospinning and then calcining. BFO can decompose up to 74.1% RhB dye in aqueous solution (5 mg/L) at cold and hot cycles of 15 °C to 45 °C. With the increase of CBO composite content from 0wt% to 10wt% in BFO nanofibers, the RhB decomposition rate of BFO@CBO heterostructure increased first and then decreased, reaching the maximum of 95% at 5wt%. The BFO@5%CBO composite with the best pyroelectrically catalytic activity had the highest bactericidal rate, and its bactericidal effect on Salmonella and Staphylococcus aureus was 96.2% and 96.8%, respectively. The increased catalytic activity of BFO@CBO may be due to the formation of heterojunctions, in which the electric field effectively separates the pyrolytic induced electron-hole under cold and hot cycles conditions. The BFO@CBO pyroelectric catalyst may have the potential to decompose dye wastewater and sterilize bacteria by collecting alternating heat energy.

Nickel-Molybdenum Carbide/Nitrogen-Doped Carbon Mott-Schottky Nanoarray for Water Spitting

Electrochemical water splitting, composed of two half reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is under intensive research to the development of H2 fuels to replace fossil fuels. Since both reactions are sluggish, catalysts are usually required to boost them. The state-of-the-art catalysts for both reactions are based on noble metals, such as Pt-based catalysts for HER and Ir or Ru-based catalysts for OER. Unfortunately, the high price and scarcity of these noble metals suppress the widespread application of water splitting. Hence, it is imperative to develop active, durable, low-cost and earth-abundant non-noble-metal electrocatalysts.[1]Among them, molybdenum carbide (Mo2C) has garnered tremendous attention as HER/OER catalysts owing to its Pt-like electronic structure and wide-pH-range catalytic performance. [2] Unfortunately, the catalytic activity of Mo2C towards HER or OER is still inferior to most advanced catalysts. One effective strategy to enhance electrocatalytic performance involves coupling and doping of Mo2C with late transition metals, e.g., Fe, Co, and Ni, which modifies electronic structure and adds active sites, metal-Mo2C interfaces. Unfortunately, similar to Mo2C, metal nanoparticles also tend to aggregate during preparation and operation. A semiconductive carbon catalyst support alleviating aggregation is usually the solution by not only conformally dispersing nanocatalysts but also providing heteroatom dopants and forming metal-semiconductor Mott-Schottky interface for further enhancing catalytic activity.[3] Besides the selection of catalysts with optimized structure and composition at the material level, the structure of electrodes derived from assembled catalysts at the device level also have a crucial influence on the water electrolyzer. Compared with powdery electrocatalysts with relatively large overpotential and easier peeling off from the electrode, self-supported hierarchical nanoarrayed electrodes are more promising for water electrolyzer because these electrodes facilitate transportation of charges and matter and thus reaction kinetics during HER/OER due to binder-free feature, catalysts-substrate seamless contact and highly exposed surface area.[4]We develop here the making of nickel-molybdenum carbide heterostructures embedded in large-area (100 cm2) hierarchically assembled nitrogen-enriched carbon, forming Mott-Schottky array on nickel foam (Ni-Mo2C/NC@NF).[5] The Ni-Mo2C/NC array is directly applied as the bifunctional catalyst with high activity and durability in alkaline electrolyte. Particularly, an extremely low overpotential of 40 mV is needed to generate hydrogen. Density functional theory calculation revealed that the formation of Ni-Mo2C Mott/NC Schottky interfaces enables favorable electronic structures for electrocatalytic water splitting. Besides, 3D hierarchical structure provides exposed active sites, facilitates mass and charge transfer, graphitic shells enhance stability. A symmetric electrolyzer using Ni-Mo2C/NC@NF generates 10 mA cm-2 at 1.59 V and operates steadily for 150 h, which even outperforms the noble metal couple, Pt/C//RuO2 for water electrolysis. The scalability, activity and durability renders Ni-Mo2C/NC@NF potential industrial application. Reference1. M. Walter, N. Lewis et al, Chem. Rev. 2010, 110, 11, 6446.2. M. Miao, B. Y. Xia, X. Wang et al, Chem. Eur. J. 2017, 23, 10947.3. F. Yu, Y. Li et al Nanoscale, 2018,10, 6080.4. H. Sun, F. Cheng., J. Chen et al. Adv. Mater. 2020, 32, 1806326.5. Z. Xu, S. Jin, M. H. Seo, X. Wang, Appl. Catal. B: Environ. 2021, 292, 120168

Electrocatalytic Hydrogen Evolution on Ferroelectric Perovskite Heterostructures

Ferroelectric perovskites have recently attracted interest for a wide range of photocatalytic and electrochemical applications1 due to their intrinsic properties for light adsorption2, electron–hole pair separation3–5 and a hypothesized enhancement of catalytic activity by polarization switching6–8. However, most of the well-known ferroelectric perovskites e.g., BaTiO3 and Pb (Zr, Ti)O3 are known to have limited activity toward electrocatalytic reactions e.g. hydrogen evolution (HER) and water splitting.2 In this work, we demonstrate that introducing only a few mono layers of SrRuO3, a metallic oxide from perovskite family, can significantly enhance the catalytic activity of BaTiO3 toward HER. Using a combination of first principle DFT+U calculations and experiments on thin films grown by molecular beam epitaxy, we investigated the activity of heterostructures of different thicknesses toward HER in an alkaline electrolyte. Computational results show that the Gibbs free energy barrier of H* adsorption on one monolayer of SrRuO3 atop ferroelectric BaTiO3 is at least two times smaller than BaTiO3, depending on the adsorption site or the direction of ferroelectric polarization. In line with the findings from our DFT calculations, our experimental results confirm significantly higher current density and lower charge transfer resistance toward hydrogen evolution for SrRuO3/BaTiO3 heterostructures compared to bare BaTiO3 surfaces. Harnessing oxide heterostructures, as demonstrated here, opens the door to leveraging the unique properties of ferroelectrics as supports to promote electrocatalytic activity.

In situ deposition of 0D CeO2 quantum dots on Fe2O3-containing solid waste NH3-SCR catalyst: Enhancing redox and NH3 adsorption ability

As NOx has been turning into a crucial environmental problem, NH3-SCR technology with relatively simple device, reliable operation and low secondary pollution, has become a widely used commercial and mature de-nitration technology. However, some weaknesses restricted the further application of commercialized V2O5-WO3/TiO2 NH3-SCR catalysts, while Fe2O3-based catalysts have received much attention due to their high thermal stability, passable N2 selectivity and low cost. In this study, Fe2O3-containing solid waste derived from Zn extraction process of electric arc furnace dust was exploited as the base material for catalyst preparing. Owing to the complementary and synergistic effect of CeO2 and Fe2O3, 0D CeO2 quantum dots (CeQDs) with fully-exposed active sites, large specific surface area, and rapid charge transfer have been introduced and deposited onto Fe2O3-containing solid waste nanorods. The in-situ deposition of CeQDs led to the admirable enhancement in NH3-SCR catalytic activity, N2 selectivity and SO2 tolerance of the extremely low-cost Fe2O3 catalyst. Comprehensive characterizations and DFT calculations describing the adsorption of O2 and NH3 were applied to analyze the catalyst structure and further investigate the detailed relationship between structural properties and activity as well as reaction mechanism. This work provides new insights for the high-value utilization of iron-containing solid waste and a practical reference for boosting the performance of NH3-SCR catalysts by introducing quantum dots.

Enhanced catalytic oxidation of dichloromethane by a surfactant-modified CeO2@TiO2 core–shell nanostructured catalyst

Surfactant-modified CeO2@TiO2 core–shell nanostructure catalysts were prepared by coprecipitation with the addition of sodium dodecyl sulfonate (SDS), and their catalytic oxidation of dichloromethane (DCM) was studied. A 90% DCM conversion efficiency is obtained at 300 °C with the CeO2@TiO2SDS catalyst, and its catalytic stability in the 55 h test period is better than that of Ce/TiO2 and CeO2@TiO2. Based on the characterization of CeO2@TiO2SDS, the dispersion of active components is promoted due to the inhibition of crystal growth with the introduction of SDS. The improvement of surface acidity and redox capacity is beneficial to the enhancement of catalytic activity. The higher adsorbed oxygen content on the surface of the CeO2@TiO2SDS catalyst is responsible for the better catalytic stability. Generally, a novel method was developed to design catalytic oxidation catalysts for the treatment of chlorinated volatile organic compounds in future applications.

Mechanism and Application of Surface-Charged Ferrite Nanozyme-Based Biosensor toward Colorimetric Detection of l-Cysteine.

Peroxidase-like nanozymes with robust catalytic capacity and detection specificity have been proposed as substitutes to natural peroxidases in biochemical sensing. However, the catalytic activity enhancement, detection mechanism, and application of nanozyme-based biosensors toward l-cysteine (l-Cys) detection still remain significant challenges. In this work, a doped ferrite nanozyme with well-defined structure and surface charges is fabricated by a two-step method of continuous flow coprecipitation and high-temperature annealing. The resulted ferrite nanozyme possesses an average size of 54.5 nm and a zeta-potential of 6.45 mV. A high-performance biosensor is manufactured based on the peroxidase-like catalytic feature of the doped ferrite. The ferrite nanozyme can oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of H2O2 because of the instinctive capacity to decompose H2O2 into ·OH. The Michaelis-Menten constants (0.0911 mM for TMB, 0.140 mM for H2O2) of the ferrite nanozyme are significantly smaller than those of horseradish peroxidase. A reliable colorimetric method is established to selectively analyze l-Cys via a facile mixing-and-detecting methodology. The detection limit and linear range are 0.119 μM and 0.2-20 μM, respectively. Taking the merits of the ferrite nanozyme-based biosensors, the l-Cys level in the human serum can be qualitatively detected. It can be anticipated that the surface-charged ferrite nanozyme shows great application prospects in the fields of bioanalytical chemistry and point-of-care testing.

Enhancement of ZnO catalytic activity under visible light by co-doping with Ga and Ti for efficient decomposition of methylene blue

Enhancement of ZnO catalytic activity under visible light by co-doping with Ga and Ti for efficient decomposition of methylene blue

Probing the promotional roles of lanthanum in physicochemical properties and performance of ZnZr/Si-beta catalyst for direct conversion of aqueous ethanol to butadiene

Here, the efficient synthesis of butadiene from aqueous ethanol was achieved over a series of x%LaZnZr/Si-beta multifunctional catalysts prepared by wet impregnation method. La species played a crucial role in improving the physicochemical properties and catalytic performance of the ZnZr/Si-beta catalyst. The structure and physicochemical properties of the synthesized catalysts were analyzed by multiple characterization technique. The characterization results revealed that the introduction of La species into ZnZr/Si-beta catalyst created a new La-O-Si bond, and rationally modified the acid-base properties. The La species substantially improved the main reaction of aldol condensation and inhibited the ethanol dehydration, as demonstrated by ethanol-TPD and TPSR studies. In addition, the adsorption capacity of water vapor was remarkably suppressed. A remarkable butadiene selectivity of 60.6 % and ethanol conversion of 83.4 % were achieved on the 5 %LaZnZr/Si-beta catalyst. This enhancement of butadiene selectivity and catalytic activity is very helpful for the development of novel efficient multifunctional catalysts for the direct synthesis butadiene from aqueous ethanol.

Poly(N,N-dimethylacrylamide)-stabilized gold nanoparticles as nanozymes with enhancement of catalytic activity for detection of lomefloxacin.

Recently, polymer-protected gold nanoparticles (AuNPs) have attracted extensive attention due to their good catalytic activities. However, how to regulate their catalytic activities by changing the polymer chain morphologies or the interactions between the ligands and the analytes through externalstimuli is still a great challenge. This study describes a simple synthesis of AuNPs capped by thermo-responsive poly(N,N-dimethylacrylamide) (PDMAM). In comparison with three kinds of PDMAMs@AuNPs, PDMAM-2@AuNPs exhibited better peroxidase-mimic ability via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) to generate oxidized TMB (oxTMB). Interestingly, its catalytic activity could be regulated by changing environmental temperature. Importantly, the addition of the antibiotic lomefloxacin endowed the PDMAM-2@AuNPs with enhancement in catalytic efficiency due to electrostatic interactions and the increased levels of reactive oxygen species. Based on this principle, a protocol for highly selective and sensitive monitoring of lomefloxacin has been constructed with the color change from pale blue to deep blue. The ultraviolet-visible absorbance of oxTMB at the wavelength of 650nm showed a good linear relationship with antibiotic concentration in the range of 0.25-10.0µM (R2 = 0.990). The limit of detection was 0.1µM. The practical application of the proposed protocol with the promoted peroxidase-mimic activity for the measurement of lomefloxacin in capsules was realized.

Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst

In the present study, two nanosized MnO2 with β and δ phase structures and potassium loaded MnO2 catalysts with varied K loading amounts (denoted as K/MnO2) were prepared. Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts. Characterization results show that as compared with β-MnO2, δ-MnO2 has larger surface area and higher content of hydroxyl groups. Upon K loading, abundant hydroxyl groups in δ-MnO2 effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%. In contrast, the majority of K species present as free state in β-MnO2 even at a K loading of 1.0 wt.% due to its very low hydroxyl group content. The O2 temperature-programmed desorption (O2-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O2, whereas the catalysts only having bound K display minor O2 activation capability. As a result, despite of slightly lower activity of β-MnO2 than δ-MnO2, the K/β-MnO2 catalysts exhibit substantially higher activities than K/δ-MnO2 catalysts with identical K loadings. The finding in this study clearly demonstrates that for MnO2 based catalysts, the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO2.

Catalytic activity enhancement of Cu2ZnSnS4 due to composite of Co9S8 as counter electrode for dye-sensitized solar cells

Catalytic activity enhancement of Cu2ZnSnS4 due to composite of Co9S8 as counter electrode for dye-sensitized solar cells

Enhancing catalytic activity of Fe3O4 for electrochemical water oxidation via the coupling of OER-inert Au

Interfacial charge transfer efficiency and electronic states of active sites are two essential issues to restrict catalytic activity of electrocatalysts for oxygen evolution reaction (OER). In this work, we show that although Au is recognized to be inert towards OER, the catalytic activity of Fe3O4 catalyst for OER was highly boosted by coupling Fe3O4 with Au to address these two issues. Here, Au nanoparticles were attached to hierarchical Fe3O4 microsphere through electrochemical deposition, a mild and rapid approach that can be accomplished within 3 min and requires no sophisticated equipment. With the coupling of Au, interfacial charge transfer resistance of Fe3O4 declined remarkably. On the other hand, oxidability of Fe sites and electron accepting capability of Au sites was elevated due to strong interaction between Au and Fe3O4. Owing to these two merits induced by Au, Fe3O4 exhibited enhanced catalytic activity for OER. The potential of Fe3O4 to obtain 10 mA/cm2 decreased by 640 mV, the current density was amplified up to 2.5 fold at the potential of 2 V (vs SCE), and the Tafel slop was reduced by 146 mV/dec.