Metal Oxide Species Research Articles

Harnessing waste Pd-based powders contaminated with ZrO2 as efficient photoelectrocatalysts for glycerol oxidation

Pd-based electrocatalysts synthesized by mechanical alloying were contaminated with ZrO2 due to an excessive process time that wore down the ZrO2 milling media balls. Instead of disposing the materials and taking into account the synergistic properties that Pd-based materials and ZrO2 could present since ZrO2 is an active oxide with photocatalytic activity, these samples were characterized through physicochemical and electrocatalytic tests, to finally be used as non-reported Pd-ZrO2-based (photo)electrocatalysts for the glycerol oxidation reaction (GOR). XRD measurements confirmed the metals alloy formation and the presence of zirconium oxide to obtain the bimetallic composites PdCo/ZrO2, PdNi/ZrO2, and PdRu/ZrO2, as well as the trimetallic PdRuCo/ZrO2 and PdRuNi/ZrO2. Physicochemical analysis showed that PdRuNi/ZrO2 presented the smallest crystallite size (14.55 nm) and the highest surface area (8.76 m2/g). Photoluminescence measurements also show that PdRuNi/ZrO2 presented the lowest emission signal, which indicates a lower charge carrier’s recombination rate. XPS measurements demonstrate the presence of different metal oxide species in alkaline medium responsible for electrostatic interactions that improve the glycerol adsorption onto the metallic centers. Electrochemical tests showed high stability for all the composites; however, the analysis of the capacitive region allowed us to calculate the electrochemical surface area (ECSA), PdRuNi/ZrO2 gave the highest value (above 7 cm−2). Confirming the results mentioned above, PdRuNi/ZrO2 showed the highest activity to carry out the electrochemical oxidation of glycerol. Regarding photoactivity, the Pd-ZrO2-based composites presented a glycerol oxidation increase up to 17 % when they were light-irradiated through a photoelectrocatalytic arrangement. PdRuNi/ZrO2 seems to be a promising material to perform the electro- but also the photoelectro- GOR in alkaline medium.

Hydrodeoxygenation of C15 furanic precursor over mesoporous NiMo-ZrO2 composite catalysts for the production of sustainable aviation fuel

Sustainable aviation fuel (SAF) is essential for achieving carbon neutrality in the transportation sector. This study elucidates the production of SAF range C9-C15 branched alkanes by hydrodeoxygenation (HDO) of C15 furanic precursor derived from 2-methylfuran and furfural via hydroxyalkylation-alkylation reaction. HDO reaction was performed using high surface area mesoporous NiMo-ZrO2 composite catalysts that exhibited high selectivity to central SAF alkanes (C13-C14). Deoxygenation follows a complex reaction network involving furanic double bond saturation and furan-ring opening reactions in series, followed by the cascade of HDO, dehydroformylation, and C-C bond cleavage. The present investigation enlightens the impact of calcination temperatures and metal (Mo and Ni) contents on structural stability, physicochemical properties, and catalytic performance of NiMo-ZrO2. Both Ni and Mo stabilized the tetragonal ZrO2 phases with improved surface area. The catalytic activity proliferated with rising calcination temperature till 873 K due to the enrichment of Mo-O-Zr acidic species and deteriorated beyond this temperature owing to the generation of crystalline MoO3/Zr(MoO4)2 species. NiMo alloy formation was enhanced, and concurrently, acidity was reduced with increasing Mo content. 30 wt% MoO3-containing catalyst showed the best catalytic activity due to the proper balance between acidity and NiMo alloy. Oxygenate conversion was boosted by increasing NiO addition up to 15 wt% due to the enhanced Ni and NiMo alloy formation and decreased at 20 wt% owing to the evolution of catalytically inactive bulk metal oxide species. Catalytic cracking was prominent at elevated reaction temperatures, with significant amounts of C13 alkane.

Effect of Bimetallic Co-Cu/Dolomite Catalyst on Glycerol Conversion to 1,2-Propanediol

This present study examines the efficacy of using dolomite (Dol, CaMg(CO3)2)-supported copper (Cu) and cobalt (Co) bimetallic and monometallic catalysts for the hydrogenolysis of glycerol to propylene glycol (PG; 1,2-PDO). The proposed catalysts were generated using the impregnation process before they were calcined at 500°C and reduced at 600°C. Advanced analytical techniques namely Brunauer, Emmett, and Teller (BET) method; the Barrett, Joyner, and Halenda (BJH) method; temperature-programmed desorption of ammonia (NH3–TPD), hydrogen-temperature programmed reduction (H2-TPR), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were then used to characterise the synthesised catalysts, whose performance was then tested in the hydrogenolysis of glycerol. Of all the synthesised catalysts tested in the hydrogenolysis process, the Co-Cu/Dol bimetallic catalyst performed best, with an 80.3% glycerol conversion and 85.9% PG selectivity at a pressure of 4 MPa, a temperature of 200°C, and a reaction time of 10 hours. Its high catalytic performance was attributed to effective interactions between its Co-Cu-Dol species, which resulted in acceptable acidity, good reducibility of metal oxide species at low temperatures, larger surface area (15.3 m2 g-1), large-sized particles, fewer pores (0.032 cm3 g-1), and smaller pore diameter (0.615 nm).

Zinc Oxide Nanoclusters Encapsulated in MFI Zeolite as a Highly Stable Adsorbent for the Ultradeep Removal of Hydrogen Sulfide.

Often, trace impurities in a feed stream will cause failures in industrial applications. The efficient removal of such a trace impurity from industrial steams, however, is a daunting challenge due to the extremely small driving force for mass transfer. The issue lies in an activity-stability dilemma, that is, an ultrafine adsorbent that offers a high exposure of active sites is favorable for capturing species of a low concentration, but free-standing adsorptive species are susceptible to rapidly aggregating in working conditions, thus losing their intrinsic high activity. Confining ultrafine adsorbents in a porous matrix is a feasible solution to address this activity-stability dilemma. We herein demonstrate a proof of concept by encapsulating ZnO nanoclusters into a pure-silica MFI zeolite (ZnO@silicalite-1) for the ultradeep removal of H2S, a critical need in the purification of hydrogen for fuel cells. The Zn species and their interaction with silicalite-1 were thoroughly investigated by a collection of characterization techniques such as HADDF-STEM, UV-visible spectroscopy, DRIFTS, and 1H MAS NMR. The results show that the zeolite offers rich silanol defects, which enable the guest nanoclusters to be highly dispersed and anchored in the silicious matrix. The nanoclusters are present in two forms, Zn(OH)+ and ZnO, depending on the varying degrees of interaction with the silanol defects. The ultrafine nanoclusters exhibit an excellent desulfurization performance in terms of the adsorption rate and utilization. Furthermore, the ZnO@silicalite-1 adsorbents are remarkably stable against sintering at high temperatures, thus maintaining a high activity in multiple adsorption-regeneration cycles. The results demonstrate that the encapsulation of active metal oxide species into zeolite is a promising strategy to develop fast responsive and highly stable adsorbents for the ultradeep removal of trace impurities.

O2 and CO2 assisted oxidative dehydrogenation of propane using ZrO2 supported vanadium and chromium oxide catalysts

Zirconia supported vanadium oxide (vanadia) and chromium oxide (chromia) catalysts of 1–3 wt% of V or Cr were prepared, characterized, and tested for the oxidative dehydrogenation (ODH) of propane (C3H8) with O2 and CO2. Characterization results reveal that 2.5% metal loading is in slight excess of monolayer loadings for this ZrO2, which has a surface area of 48 m2.g−1. The reaction results reveal that supported vanadia catalysts are better for O2-ODH and supported chromia catalyst are better for CO2-ODH at a reaction temperature of 550 °C. Furthermore, the C3H8 conversion and propene (C3H6) yield increases with loading and the highest conversion and yield are also achieved at 2.5% metal loading. With higher loadings the conversion and yield decreases, clearly indicating that the surface metal oxide species are more active than their crystalline counterparts. As the contact time increases, for inlet stoichiometric ratios of the reactants for the two reactions, C3H8/CO2 = 1 and C3H8/O2 = 2, C3H8 conversion and C3H6 yield both monotonically increase and appear to approach a constant value; however, the difference between C3H8 conversion and C3H6 yield also increases. The C3H6 selectivity during O2-ODH (∼30%) is much lower than C3H6 selectivity during CO2-ODH (86–94%). Furthermore, during CO2-ODH of propane the conversions of C3H8 and CO2 are similar, and it appears that under the operating conditions used, the dry reforming of propane does not occur. Overall, the CO2-ODH of propane reaction at 550 °C using stoichiometric ratios of C3H8/CO2 over ZrO2 supported chromia catalyst provides a better C3H6 yield and selectivity, with an additional advantage of converting CO2.

Antimicrobial Effect of Submicron Complex Oxide Particles CsTeMoO6 under Visible Light

The antimicrobial activity of submicron particles of new photocatalytic active complex metal oxide CsTeMoO6 against bacteria Escherichia coli and Staphylococcus aureus and fungi Aspergillus niger and Penicillium chrysogenum (spores and vegetative mycelium) was studied. It has been established that CsTeMoO6 has the antimicrobial activity in both under dark and visible light conditions in relation to all test cultures of microorganisms. The most inhibitory effect of CsTeMoO6 was noted for E. coli. The light enhanced the antimicrobial effect of the test compound against all cultures of bacteria and fungi, which is associated with the presence of photocatalytic activity of CsTeMoO6. The antifungal activity of CsTeMoO6 increased against spores and vegetative mycelium of fungi under light condition, and this effect increased with an increasing duration of time exposure. The different degree of survival rate of the studied microorganisms in the presence of this compound (under both dark and light) may be associated with the physiological and biochemical characteristics of the used microorganisms, including different mechanisms of resistance against complex metal oxide and reactive oxygen species.

Sustainable Production of Chemicals via Hydrotreating of CO2 and Biomass Derived Molecules Using Heterogeneous Noble Metal Oxide Catalysts

AbstractThe noble metals are widely used in heterogeneous catalysis and automobile industry. The limited natural sources and high cost of noble metals dictates improving the efficiency of modern industry. This review considers the applications of noble metal oxide as potential solutions to the sustainability issues, including biomass conversion, CO2 capture and conversion, green fuel production, etc. Noble metal oxides with their different compositions (monometallic and bimetallic) and structures exhibit a wide range of properties in heterogeneous catalysis. Although platinum metals in an oxidized form may not be the most common choice in hydroprocesses; recently, there have been studies indicating that they were highly active and selective catalysts in hydrogenation and hydrogenolysis. This review outlines the most established noble metal oxide catalysts used in hydrogenation catalysis and shed the light on the relation of noble metal oxide species to catalyst selectivity based on state‐of‐the‐art techniques. Finally, the perspectives on the application of noble metal oxide catalysts to produce value‐added chemicals are discussed.

Production of synthesis gas from dry reforming of propane with carbon dioxide over ceria-promoted nickel foam catalysts

A series of nickel foam supported cerai catalysts (ceria/NiF) for dry reforming of propane with carbon dioxide were prepared and their performance were evaluated at temperatures in the range of 520-600°C. Among the catalysts examined the 4 wt.% CeO2/NiF exhibited better low-temperature activity for the DRP, which is attributed to the formation of well- isolated nanosize CeO2 particles and highly reducible metal oxide species over the NiF support. The XPS and temperature programmed reduction (TPR) data also supported the incorporation of ceria into the NiO surface layer formed over NiF support, which was substantially higher in 4% CeO2/NF catalyst. Due to these favorable properties, the 4 wt.% CeO2/NiF could be considered as an excellent catalyst for DRP.

Catalytic oxidation of toluene over highly dispersed Mn-Ce solid solutions synthesized with weakly acidic precursors

In this paper, a series of Mn-Ce composite oxide catalysts were prepared by different preparation methods using different Mn and Ce acidic precursors for the catalytic oxidation of toluene. The activity test results revealed that the Mn-Ce composite catalysts, synthesized through the sol-gel method using weakly acidic Mn acetate and Ce acetate as precursors, exhibited the highest performance for the catalytic oxidation of toluene. The T50 and T90 values for this catalyst were measured at 208 °C and 235 °C, respectively. The relatively weak acidity of manganese acetate and cerium acetate facilitates the presence of acidic -OH groups, which interact with the oxygen-negative charge sites on each other. Furthermore, during the calcination process, there was a strong interaction between hydrated Mn and Ce ions, resulting in the formation of highly dispersed metal oxide species. The formation of Mn-Ce solid solution demonstrated by Raman, XRD. The H2-TPR characterization indicated that the superior redox performance of the MnOx species on the catalyst surface played a pivotal role in achieving high activity. Moreover, the catalytic activity of the CeO2 species was further enhanced by employing the sol-gel method. XPS and O2-TPD results revealed a significantly higher amount of reactive oxygen species on the catalyst surface, which was identified as the primary reason for the increased activity. This study provides a new strategy for the selection of the catalyst precursors, thereby enhancing the catalytic activity of Mn-Ce composite oxides.

Structure and Reactivity of Metal-Oxide-Supported Noble Metal Nanoparticles: Electrooxidation of Simple Organic Molecules

There has been growing interest in utilizing small (simple) organic molecules, as alternative fuels to hydrogen, in electrochemical energy conversion systems. In addition to ethanol (biofuel), that can be ideally oxidized to carbon dioxide thus delivering twelve electrons, recent important systems include dimethyl ether as well. But realistically the respective reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials.Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium.We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol, ethanol, formic acid and dimethyl ether. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

Energy-saving catalyst Fe/Ce-Mn-TiO2 for efficient low temperature NH3-SCR of NOx with high water content

An energy-saving catalyst 4%Fe/Ce-Mn-TiO2 was prepared via a simple one-step impregnation-annealing process and used as a denitration catalyst at low temperature (≤180 °C) and high water content (∼20%). The results show that 4%Fe/Ce-Mn-TiO2 catalyst exhibits good low-temperature catalytic activity and water resistance attributed to its highly dispersed metal oxide species, more surface-adsorbed oxygen and high stability of particles. The denitrification efficiencies of 4%Fe/Ce-Mn-TiO2 catalyst are 90% (5% H2O) and 70% (20% H2O) at 170 ℃ respectively, which are superior to the commercial vanadium catalyst in service usually needs heating up to 220 ℃.

Synthesis of Tb2O3/ZnO composite nanofibers via electrospinning as chemiresistive gas sensor for detecting NO gas

Forming nanocomposites among different metal oxide species may lead to gas sensors with superior gas sensing properties. In this work, terbium oxide (Tb2O3) was used to form composite nanofibers with zinc oxide (ZnO) to detect nitric oxide (NO) gas. The Tb2O3/ZnO composite nanofibers were synthesized through a facile electrospinning and annealing treatment. The heterostructure was investigated by various techniques such as XRD, SEM, TEM, and XPS, whereas the gas sensing performance of the composite nanofibers was investigated with a static gas testing system. Results showed that the Tb2O3/ZnO composite nanofiber exhibited excellent sensing performance to NO at 180 °C. Specifically, the composite nanofiber with [Tb]/[Zn] molar ratio of 0.01 had a high response of 28.3 (resistance ratio) to 1 ppm NO gas at 180 °C, with low response to other interference gases. The sensor also exhibited good repeatability and long-term stability. These remarkable sensing properties indicate that conventional ZnO is still promising for real applications via material composition and structure.

Influence of Zn and Fe promoters on Ni-Bi/γ-Al2O3 catalyst for oxidative dehydrogenation of n-butane to butadiene

This study investigated the effects of Zn and Fe metal oxide species as promoters on NiO-Bi2O3/γ-Al2O3 in the oxidative dehydrogenation (ODH) of n-butane to produce butadiene. Ni-Bi-O, Ni-Zn-Bi-O, Ni-Fe-Bi-O, and Ni-Zn-Fe-Bi-O catalysts supported on γ-Al2O3 were synthesized, characterized, and evaluated in a packed bed flow reactor at different temperatures and O2/n-butane molar ratios. Substituting 50 wt.% of Ni with one or both promoters were found to enhance both the butadiene selectivity. Among the synthesized catalysts, Ni-Zn-Fe-Bi-O/γ-Al2O3 (10 wt.% Ni-5 wt.% Zn-5 wt.% Fe-30 wt.% Bi) showed the highest butadiene selectivity of 49.0% with 18.6% n-butane conversion at 450 °C and a molar feed ratio of O2/n-butane = 2.0. This enhanced performance was attributed to the synergetic effects of Ni, which simultaneously improved the first-step dehydrogenation selectivity via a promotion with Zn and the second-step dehydrogenation selectivity by the incorporation of Fe. Moreover, Zn allowed the surface reduction to occur at lower temperatures, while Fe balanced the densities of strong basic sites with weak and moderate acid sites (0.183 mmol CO2/g-cat and 0.188 mmol NH3/g-cat, respectively). The aforementioned results were confirmed with CO2/NH3 temperature-programmed desorption and H2 temperature-programmed reduction experiments. Under this reaction condition, the catalyst maintains good stability over 15 h of time-on-stream.

Exploring the Multifunctionality of Mechanochemically Synthesized γ-Alumina with Incorporated Selected Metal Oxide Species

γ-Alumina with incorporated metal oxide species (including Fe, Cu, Zn, Bi, and Ga) was synthesized by liquid-assisted grinding-mechanochemical synthesis, applying boehmite as the alumina precursor and suitable metal salts. Various contents of metal elements (5 wt.%, 10 wt.%, and 20 wt.%) were used to tune the composition of the resulting hybrid materials. The different milling time was tested to find the most suitable procedure that allowed the preparation of porous alumina incorporated with selected metal oxide species. The block copolymer, Pluronic P123, was used as a pore-generating agent. Commercial γ-alumina (SBET = 96 m2·g-1), and the sample fabricated after two hours of initial grinding of boehmite (SBET = 266 m2·g-1), were used as references. Analysis of another sample of γ-alumina prepared within 3 h of one-pot milling revealed a higher surface area (SBET = 320 m2·g-1) that did not increase with a further increase in the milling time. So, three hours of grinding time were set as optimal for this material. The synthesized samples were characterized by low-temperature N2 sorption, TGA/DTG, XRD, TEM, EDX, elemental mapping, and XRF techniques. The higher loading of metal oxide into the alumina structure was confirmed by the higher intensity of the XRF peaks. Samples synthesized with the lowest metal oxide content (5 wt.%) were tested for selective catalytic reduction of NO with NH3 (NH3-SCR). Among all tested samples, besides pristine Al2O3 and alumina incorporated with gallium oxide, the increase in reaction temperature accelerated the NO conversion. The highest NO conversion rate was observed for Fe2O3-incorporated alumina (70%) at 450 °C and CuO-incorporated alumina (71%) at 300 °C. The CO2 capture was also studied for synthesized samples and the sample of alumina with incorporated Bi2O3 (10 wt.%) gave the best result (1.16 mmol·g-1) at 25 °C, while alumina alone could adsorb only 0.85 mmol·g-1 of CO2. Furthermore, the synthesized samples were tested for antimicrobial properties and found to be quite active against Gram-negative bacteria, P. aeruginosa (PA). The measured Minimum Inhibitory Concentration (MIC) values for the alumina samples with incorporated Fe, Cu, and Bi oxide (10 wt.%) were found to be 4 µg·mL-1, while 8 µg·mL-1 was obtained for pure alumina.

A comparative study of zirconia supported nickel and/or ruthenium catalysts for glycerol steam reforming

The physico-chemical properties of Ni, Ru, Ru–Ni monoclinic ZrO2 catalysts were studied and their catalytic activities in the glycerol steam reforming reaction (GSR) were compared. The catalysts were prepared by the wet impregnation method, calcined at 600 °C and characterized using XRD, BET, H2-TPR and CO2-TPD techniques. The XRD analyses revealed varying crystallite sizes depending on the active phase nature and composition. The H2-TPR analyses demonstrated that the reducibility of the active metal oxide species and its dispersion were affected by the active phase composition. The CO2-TPD analyses revealed that surface modification following impregnation modified the basic properties of the catalysts. The catalytic activity tests (T = 400–700 °C, WGFR 9:1, flow rate of 0.025 mL/min) showed that the nickel based catalysts were active while the ruthenium based catalyst was inactive. Combining ruthenium and nickel over zirconia led to smaller Ni particle sizes and a better metal dispersion both of which contributed to higher H2 yields and an increased coke resistance. During 24 h on stream, the combined Ru–Ni/ZrO2 catalyst maintained a higher total glycerol conversion compared to the Ni/ZrO2 catalyst. Only filamentous coke was identified on the spent catalysts after the stability tests. For a higher water to glycerol feed ratio (WGFR 46:1), encapsulating coke was formed over Ru–Ni/ZrO2 leading to the blockage of active sites and a more rapid catalyst deactivation.

Polyoxometalate Cluster-Incorporated High Entropy Oxide Sub-1 nm Nanowires.

High entropy oxides (HEOs) with fascinating physical and chemical properties have exhibited unprecedented application potential in many fields. However, it remains a huge challenge to realize the precise control of the dimension and morphology at the sub-1 nm scale. Herein, with the aid of polyoxometalate (POM) clusters, we first develop a versatile strategy to realize the controllable incorporation of multiple immiscible metal oxides into sub-1 nm nanowires (SNWs) under 140 °C to obtain a wide range of HEO-POM SNWs with highly ordered structures, where the species of metal oxides and POMs could be regulated flexibly. Meanwhile, these obtained HEO materials are first to be used as anodes in Na-ion batteries. Benefiting from the effect of entropy modulation, these HEO-POM SNWs show better electrochemical properties in Na-ion batteries with the increase of metal oxide species stepwise. A long cycle life with a capacity retention of ∼92% even after 5000 cycles at 10C further confirms the good stability under fast discharging/charging. This method opens a new insight for designing and preparing HEOs at the sub-1 nm scale under facile conditions.

Novel noble metal-free and recyclable Co-CoOx-FeNiCo/γ-Al2O3 catalyst for selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran or 2,5-Bis(hydroxymethyl)furan

The efficient production of the liquid fuel 2,5-dimethylfuran (DMF) from biomass-derived 5-hydroxymethylfurfural (HMF) is very complicated because of the presence of the aldehyde group, hydroxyl group, and CC bond. In this study, a novel Co-CoOx –FeNiCo/γ-Al2O3 catalyst was developed for selective hydrogenation of HMF to DMF. The catalyst was characterized by using XRD, TEM, SAED, BET, XPS, NH3-TPD, and H2-TPR techniques. The catalyst reduced at 500 °C exhibited excellent catalytic performance and the highest DMF yield (>99.9%) was obtained at 190 °C and 4 h. During the reaction, metal sites selectively hydrogenated the CO bond while acid sites (CoOx acid sites) selectively hydrogenolyzed CO bond. Appropriate surface acidity of the catalyst and the balance between metal and metal oxide species are the main factors for achieving a high yield of DMF. At reaction temperatures below 150 °C, DMF was not produced and HMF has completely converted into 2,5-Bis(hydroxymethyl)furan (BHMF), an important furan diol for polymers production. 100% BHMF yield was also obtained for the HMF hydrogenation over 300 °C reduced catalysts due to the high concentration of strong acid sites. The catalyst recyclability exhibited excellent stability and the original activity was maintained after six reuses. A reaction mechanism was also proposed.

Novel preparation of functional β-SiC fiber based In2O3 nanocomposite and controlling of influence factors for the chemical gas sensing

The gas sensing ability of a pure β-SiC fiber is limited due to its low-sensitivity and selectivity with poor recovery time during a gas sensing test. The combination of functional β-SiC fibers with metal-oxide (MO) can lead to excellent electronic conductivity, boosted chemical activity, and high reaction activity with the target gas and β-SiC–In2O3 sensor material. Influence factors such as amounts of MO, current collectors, and gas species (CO2, O2 and without gas) for the gas sensing ability of β-SiC–In2O3 nanocomposite were determined at standard room temperature (25 °C) and high temperature (350 °C) conditions. The gas sensing ability of the functional β-SiC fiber was significantly enhanced by the loading of In2O3 metal-oxide. In addition, the MO junction on the β-SiC fiber was mainly subjected to the Si–C–O–In bond sensor layer with an effective electron-transfer ability. The gas sensing mechanism was based on the transfer of charges, in which the sensing material acted as an absorber or a donor of charges. The sensor material could use different current- collectors to support the electron transfer and gas sensing ability of the material. A 1:0.5M SiC–In2O3 coated Ni-foil current collector sensor showed better sensing ability for CO2 and O2 gases than other gas sensors at room temperature and high temperature conditions. The sensing result of the electrode was obtained with different current density values without or with gas purging conditions because CO2 and O2 gases had electron acceptor properties. During the gas sensing test, the sensor material donated electrons to target gases. The current value on the CV graph then significantly changed. Our obtained sample analysis data and the gas sensing test adequately demonstrated that MO junctions on functional β-SiC fibers could improve the sensitivity of a sensor material and particularly upgrade the sensor material for gas sensing.

Cobalt oxide confined in mesoporous SiO2 as effective catalyst for CO oxidation

Ordered mesoporous SiO 2 samples (SBA-15) with different pore sizes were prepared as carriers, and a series of catalysts (CoO x @SBA-15( X )) were synthesized to confine CoO x in SBA-15 through the solid-state grinding method for CO oxidation. The characterization results showed that the aggregation of CoO x in the pores of the carrier SBA-15 was effectively inhibited by the confinement effect, which further facilitated the formation of the main catalytic site Co(III) species. The results of the density-functional theory calculations further confirmed that Co(III) was the important catalytic site for CO oxidation. Compared with the catalyst prepared through the impregnation method, catalysts CoO x @SBA-15( X ) exhibited a lower CO conversion temperature and activation energy for CO oxidation. In addition, the pore size of the carrier SBA-15 had a significant impact on the catalytic activity of CoO x , and the catalyst prepared with a larger pore size SBA-15 as carrier exhibited a higher catalytic activity. This result was mainly attributed to the fact that the confinement effect could effectively enhance the defect formation in metal oxides. Furthermore, the catalyst with a larger pore size SBA-15 as a carrier presented a higher content of Co(III) species, which significantly enhanced the catalytic activity of CoO x for CO oxidation. The results demonstrated that the pore structure of SBA-15 could affect the formation of the metal oxide (CoO x ) species, which further significantly affected the catalytic activity of CoO x for CO oxidation. The results are expected to provide a strategy to synthesize efficient catalysts for CO oxidation by using ordered mesoporous materials. • Solid state grinding method is an effective way to confine CoO x in SBA-15 pores. • Confinement effect could enhance the catalytic activity of catalysts for CO oxidation. • SBA-15 with larger pore size was more favorable for the formation of Co(III) species.

Structure-Function Correlations in the Mechanism of Action of Key Antiperspirant Agents Containing Al(III) and ZAG Salts.

Aluminum hydrolysis chemistry is an important part of modern society because of the dominance of Al(III) as a highly effective antiperspirant active. However, the century-old chemistry centered on aluminum chloride (ACL) is not comprehensive enough to address all of the in vivo events associated with current commercial antiperspirants and their mechanism of action. The present study aims to address the knowledge gap among extensively studied benchmark ACL, its modified version aluminum chlorohydrate (ACH), and a more complex but less explored group of aluminum zirconium chlorohydrate glycine complexes (ZAG salts) toward understanding the mechanism of action under consumer-relevant conditions. ACH, which is the Al source used in the manufacture of ZAG salts, provides a bridge between ACL and ZAG chemistry. High viscosity and gel formation driven by pH and a specific Al(III) salt upon hydrolysis are considered the criteria for building an in vivo occlusive mass to retard or stop the flow of sweat to the skin surface, thus providing an antiperspirant effect. Rheological studies indicated that ACL and aluminum zirconium tetrachlorohydrex glycine (TETRA) were the most efficacious salt actives. Spectroscopic studies, diffraction studies, and elemental analysis suggested that small metal oxide and hydroxide species with coparticipating glycine as well as various polynuclear and oligomeric species are the key to gel formation. At a given pH, the key ingredients (NaCl, urea, bovine serum albumin, and lactic acid) in artificial sweat were found to have little influence on Al(III) salt hydrolysis. The effects of the sweat components were mostly limited to local complex formation and kinetic modification. The in vitro comparative experiments with various Al(III) and ZAG salt systems offer unprecedented insights into the chemistry of different salt types, thus paving the way for engineering more efficacious antiperspirant systems.