Mesoporous Mn promoted Co3O4 oxides as an efficient and stable catalyst for low temperature oxidation of CO

Mesoporous Mn-doped Co₃O₄ catalysts were successfully prepared via a dry soft reactive grinding method based on solid state reaction, and their catalytic performances on CO oxidation were evaluated at a high space velocity of 49,500 mL g⁻¹ h⁻¹. A significant promoted effect was observed once the atomic ratios of Mn/(Co+Mn) were lower than 10%, for instance, the temperature for 50% conversion decreased to about −60 °C, showing superior catalytic performance compared to the single metal oxide. Especially, the Mn-promoted Co₃O₄ catalyst with a Mn/(Co+Mn) molar ratio of 10% could convert 100% CO after 3000 min of time-on-steam without any deactivation at room temperature. As prepared catalysts were characterized by XRD, N₂-adsorption/desorption, TEM, H₂-TPR, O₂-TPD and CO-titration analysis. The significant enhancement of performance for oxidation of CO over Mn-Co-O mixed oxides was associated with the high active oxygen species concentrations formed during the pretreatment in O₂ atmosphere.     

Ag@ Fe-TiO2 catalysts for catalytic oxidation of formaldehyde indoor: a further improvement of Fe-TiO2

In this paper, a series of Fe-doped TiO₂ (Fe-TiO₂) catalysts were prepared by ultrasonic hydrothermal method and were used to catalytic oxidation formaldehyde (HCHO) indoor at room temperature. Although the catalytic activity was improved compared with P25, but the final concentration of HCHO was still higher than the Chinese standard (GB 0.08 mg/m³), and the stability was restrict under room temperature. In order to improve the catalytic activity and stability of the catalysts, various concentrations of Ag were loaded on Fe-TiO₂, and good catalytic oxidation effect was obtained and had a good repeat catalytic effect under room condition. UV–Vis, IR, PL, XRD, SEM, BET, XPS were used to characterize the materials. The results showed that the higher dispersion of active Ag, and the synergistic effect between Ag, Fe and TiO₂ nanostructure were helpful to improve the catalytic oxidation ability of Ag@Fe-TiO₂. In the repeat experiments, 0.6%Ag@0.3%Fe-TiO₂ exhibited good catalytic activity and stability. The formaldehyde concentration was reduced to 0.05 mg/m³, after four rounds of tests, the formaldehyde concentration was still below 0.08 mg/m³, applying for long time indoor HCHO degradation at room temperature. Indicating the modification of Ag element can further promote the catalytic activity and stability of Fe-TiO₂.

     

CTAB assisted hydrothermal synthesis, controlled conversion and CO oxidation properties of CeO2 nanoplates, nanotubes, and nanorods

In this work, CeO₂ nanoplates were synthesized by a hydrothermal reaction assisted by hexadecyltrimethylammonium bromide (CTAB) at 100-160 °C. The size of nanoplates was around 40 nm. Further experiment showed that the controlled conversion of nanoplates into nanotubes, and nanorods can be realized by changing the reaction time, temperature, and CTAB/Ce³⁺ ratio value. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption measurements were employed to characterize the samples. The CO oxidation properties of nanorods, nanoplates, and nanotubes were investigated. An enhanced catalytic activity has been found for CO oxidation by using CeO₂ nanoplates as compared with CeO₂ nanotubes and nanorods, and the crystal surfaces (100) of CeO₂ nanoplates were considered to play an important role in determining their catalytic oxidation properties.     

Construction of Cu-Ce interface for boosting toluene oxidation: Study of Cu-Ce interaction and intermediates identified by in situ DRIFTS

A facile hydrothermal method was applied to gain stably and highly efficient CuO-CeO₂ (denoted as Cu1Ce2) catalyst for toluene oxidation. The changes of surface and inter properties on Cu1Ce2 were investigated comparing with pure CeO₂ and pure CuO. The formation of Cu-Ce interface promotes the electron transfer between Cu and Ce through Cu²⁺ + Ce³⁺ ↔ Cu⁺ + Ce⁴⁺ and leads to high redox properties and mobility of oxygen species. Thus, the Cu1Ce2 catalyst makes up the shortcoming of CeO₂ and CuO and achieved high catalytic performance with T₅₀ = 234 °C and T₉₉ = 250 °C (the temperature at which 50% and 90% C₇H₈ conversion is obtained, respectively) for toluene oxidation. Different reaction steps and intermediates for toluene oxidation over Cu1Ce2, CeO₂ and CuO were detected by in situ DRIFTS, the fast benzyl species conversion and preferential transformation of benzoates into carbonates through C=C breaking over Cu1Ce2 should accelerate the reaction.     

Voltammetric evaluation of the electrode material on the oxidation of cyanide catalyzed by copper ions

The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN^–, Cu(CN)₄^3– or Cu(CN)₄^2– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)₄^3– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN^– controlled the global process. However, in all cases, the adsorption of Cu(CN)₄^3– on the electrode surface was required for the catalytic oxidation of CN^–. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)₂ and cyanate (CNO^–), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN^– depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)₂ tended to adosorb on VC, while the formation of cyanate, CNO^– predominated on SS 304.     

High performance CuO-CeO2 catalysts for selective oxidation of CO in excess hydrogen： Effect of hydrothermal preparation conditions

High performance CuO-CeO₂ catalysts for selective oxidation of CO in excess hydrogen were prepared by a hydrothermal method under different preparation conditions and evaluated for catalytic activities and selectivities. By changing the n_CTAB/n_Ce ratio and hydrothermal aging time, the catalytic activity of the CuO-CeO₂ catalysts increased and the operating temperature window, in which the CO conversion was higher than 99%, was widened. XRD results showed no peaks of CuO_x species and Cu-Ce-O solid solution were observed. On the other hand, Cu⁺ species in the CuO-CeO₂ catalysts, which was associated with a strong interaction between copper oxide clusters and cerium oxide and could be favorable for improving the selective oxidation performance of CO in excess H₂, were detected by H₂-TPR and XPS techniques.     

One pot synthesis of chromium incorporated SBA-16 under acid medium-Application in the selective oxidation of benzyl alcohol derivatives

Cr-SBA-16 mesoporous silica heterogeneous catalysts (Si/Cr = 7, 14, and 28) were successfully synthesized by one-pot hydrothermal method at low acidic medium. The catalysts were characterized by means of X-ray diffraction (XRD), N₂ adsorption-desorption at 77 K, Fourier Transform Infrared (FTIR), X-ray photoelectron (XPS) and Diffuse Reflectance UV–Vis (DRS) Spectroscopies, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques. Herein, Cr-SBA-16 catalysts are evaluated in the selective catalytic oxidation of benzyl alcohol derivatives using H₂O₂ as oxidant. From XPS and UV–Vis (DRS) spectroscopies the molar ratios between Cr⁶⁺/Cr³⁺ are found to increase versus chromium loading in the following order: Cr-SBA-16(28) < Cr-SBA-16(14) < Cr-SBA-16(7). Hence the highest Cr⁶⁺ in tetrahedrally environment is observed for Si/Cr = 7. We demonstrated for the first time that the selective catalytic oxidation of benzyl alcohol (BzOH) using H₂O₂ over Cr-SBA-16 occurs through noncompetitive adsorption mechanism and the reaction is pseudo-first order to BzOH. The activity of the reaction depends on the symmetry of chromium species, herein, high activity is observed for tetrahedral chromium species in Cr-SBA-16(7). The absence of any chromium ions in the filtrate shows no chromium leaching from the silica framework.     

Chemical modification of poly(vinyl chloride) by nucleophilic substitution

The reaction of poly(vinyl chloride) (PVC) in nucleophile (Nu)/ethylene glycol (EG) or Nu/N,N-dimethylformamide (DMF) solution was found to result in the substitution of Cl in PVC with Nu from solution, in addition to the straight elimination of HCl, both of which led to the dechlorination of PVC. Examined Nu⁻ were I⁻, SCN⁻, OH⁻, N₃⁻, and the phthalimide anion. For the Nu/EG solution, elimination was favoured over substitution for all Nu⁻. The ratio of substitution to dechlorination was notable, descending in the order OH⁻ > SCN⁻ = N₃⁻ > phthalimide anion > I⁻. For the Nu/DMF solution, the ratio of substitution to dechlorination was high, in the order SCN⁻ > N₃⁻ > I⁻ > phthalimide anion. In both cases, the orders of the ratios were similar to those of the nucleophilic reactivity constant, I⁻ > SCN⁻ > N₃⁻ > phthalimide anion, except for I⁻. The low ratio for I⁻ was attributable to the elimination of HI after the substitution of Cl in PVC with I in solution, because I⁻ is a strong nucleophile, as well as an excellent leaving group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for I⁻, SCN⁻, N₃⁻, and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG.     

Influence of hydrothermal synthesis temperature on the redox and oxygen mobility properties of manganese oxides in the catalytic oxidation of toluene

A series of MnO_x samples synthesized by hydrothermal methods at different temperatures were investigated as catalysts for the oxidation of toluene. The optimum oxidation performance was achieved with the catalyst prepared at 120 °C (Mn-120), for which complete conversion of toluene was attained at 250 °C. The Mn-120 sample possessed the highest concentration of Mn³⁺ and the highest initial H₂ consumption rate, which are indicative of abundant crystal defects and superior reducibility. In addition, Mn-120 exhibited excellent oxidation ability due to the abundance of lattice oxygen species and excellent oxygen mobility. Therefore, the superior catalytic performance of Mn-120 could be attributed mainly to its redox performance and abundant crystal defects, both of which are determined by the temperature of the hydrothermal synthesis of MnO_x.

     

Triazole‐based ligands functionalized silica: Effects of ligand denticity and donors on catalytic oxidation activity of Pd nanoparticles

Triazole‐based ligands, tris (triazolyl)methanol (Htbtm), bis (triazolyl)‐phenylmethanol (Hbtm), and phenyl (pyridin‐2‐yl)(triazolyl)methanol (Hpytm), with differences in ligand denticity (i.e., bidentate and tridentate) and type of N donors (i.e., triazole and pyridine) were functionalized onto a silica support to produce the corresponding SiO₂‐ L ( L  = tbtm, btm, pytm). Subsequent reactions with Pd (CH₃COO)₂ in CH₂Cl₂ yielded Pd/SiO₂‐ L . ICP‐MS reveals that Pd loadings are higher with increased N loadings, resulting in the following trend: Pd/SiO₂‐tbtm (0.83 mmol Pd g^?1) > Pd/SiO₂‐btm (0.65 mmol Pd g^?1) ~ Pd/SiO₂‐pytm (0.63 mmol Pd g^?1). Meanwhile, TEM images of the used Pd/SiO₂‐ L catalysts after the first catalytic cycle show that the mean size of Pd NPs is highest with Pd/SiO₂‐pytm (8.5 ± 1.5 nm), followed by Pd/SiO₂‐tbtm (6.4 ± 1.6 nm) and Pd/SiO₂‐btm (4.8 ± 1.3 nm). Based on TONs, catalytic studies toward aerobic oxidation of benzyl alcohol to benzaldehyde at 60 °C in EtOH showed that Pd/SiO₂‐pytm possessed the most active surface Pd(0) atoms, most likely as a result of more labile properties of the pyridine–triazole ligand compared to tris‐ and bis (triazolyl) analogs. ICP‐MS and TEM analysis of Pd/SiO₂‐btm indicate minimal Pd leaching and similar average Pd NPs sizes after 1^st and 5^th catalytic runs, respectively, confirming that SiO₂‐btm is an efficient Pd NPs stabilizer. The Pd/SiO₂‐btm catalyst was also active toward aerobic oxidation of various benzyl alcohol derivatives in EtOH and could be reused for at least 7 reaction cycles without a significant activity loss.     

Kinetics of wet air oxidation of sodium sulfide over heterogeneous iron catalyst

Wet air oxidation (WAO) is an established technique for reducing the chemical oxygen demand (COD) of refinery sulfidic spent caustic waste. In the present work, the heterogeneous form of the cheap and abundant catalyst ferrous sulfate (FeSO₄) was employed for WAO of sodium sulfide. The performance of this catalyst in the oxidative destruction of this model compound is thus far unfamiliar. Kinetic data for the non-catalytic and catalytic oxidation processes was collected in a batch reactor. For the catalytic process, temperature (T), oxygen partial pressure () and catalyst concentration (ω) were varied in the ranges 80-150°C, 0.69-2.06 MPa and 0.8-2.4 g/L respectively. Around 94% COD was destroyed within 1 h when feed containing 8 g/L of sulfide was oxidized at T = 100°C, = 0.69 MPa, and ω = 0.8 g/L. First, the data on disappearance of COD were fitted to a power law model and reaction rate constants were determined. The activation energy for the non-catalytic (91 kJ/mol) and catalytic (50 kJ/mol) oxidation process was found from the temperature dependence of the rate constants. Second, hyperbolic models based on Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-L) kinetics were used for fitting kinetic data. It was found that the L-H model suggesting dissociative adsorption of oxygen provided the best fit. In this way, a deep insight into oxidation kinetics of sodium sulfide was provided.     

Activating P2-NaxCoO2 for efficient water oxidation catalysis via controlled chemical oxidation

Electrocatalytic water oxidation is critically important for a wide range of emerging energy conversion devices. Co-based metal oxides are very promising candidates as high-performance oxygen evolution reaction (OER) catalysts. Here, it is shown that chemical oxidation of layered P2-Na_xCoO₂ could lead to compositionally tunable P2-Na_xCoO₂ with high OER activity. The optimal electrocatalytic activity emerges in a narrow range of sodium concentrations with Na_0·28CoO₂ exhibiting the lowest overpotential of 350 mV at 10 mA/cm² and a Tafel slope of 29 mV/dec in 0.1 M NaOH electrolyte, outperforming the benchmark RuO₂ catalyst and previous LiCoO₂-based electrocatalysts. Electrochemical measurements and X-ray spectroscopic investigations reveal that chemically oxidized P2-Na_xCoO₂ catalysts are intrinsically active toward OER, arising from the abundant oxygen vacancies, increased Co-O covalency, and enhanced conductivity after deintercalation of the Na⁺. Our findings provide new insights into the design and synthesis of cost-effective catalysts toward efficient and durable OER.     

Enhanced catalytic activity of composites of NiFe2O4 and nano cellulose derived from waste biomass for the mitigation of organic pollutants

This study reports facile in situ synthesis of magnetically retrievable nanocomposites of nanocellulose (derived from waste biomass) and NiFe₂O₄ nanoparticles using hydrothermal method. The synthesized nanocomposites were characterized using various techniques such as FT-IR, powder XRD, HR-TEM, BET and VSM. The characterization of nanocomposites clearly revealed that NiFe₂O₄ nanoparticles were well dispersed on the surface of cellulose nanofibres. The catalytic performance of the synthesized nanocomposites was assessed for both the photocatalytic oxidation and reduction of organic pollutants. The prepared nanocomposites displayed excellent catalytic performance in comparison to pristine NiFe₂O₄ nanoparticles due to stabilization and increased dispersability of NiFe₂O₄ nanoparticles on the cellulose matrix. The present work promotes the use of bio based renewable sources to fabricate environment friendly materials to be used in the field of catalysis for the abatement of organic pollutants.     

Optimization of multiple parameters for treatment of coking wastewater using Fenton oxidation

Present study deals with the treatment of coking wastewater (CWW) using Fenton oxidation process for the degradation of pollutants containing chemical oxygen demand (COD), phenol and cyanide. The experiments were performed in batch mode to study the effect of operating parameters like initial pH (pH_i), temperature (T), oxidant H₂O₂ amount, catalyst mass loading (Cw) and treatment time (t_R). The response surface methodology (RSM) gave optimum value of pH, H₂O₂, Cw and t_R as 3, 0.3 M, 1.85 g/L (0.0266 M) and 1.52 h. At this optimum operating condition maximum 84.66% COD, 88.46% phenol and 79.34% cyanide reduction were achieved from initial value of COD (COD_i) = 2810.0 mg/L, phenol_i = 283.0 mg/L and cyanide_i = 18.88 mg/L. Results reflect that Fenton oxidation is an effective process for the reduction of pollutants present in CWW. The CWW treated by Fenton oxidation having average value COD = 590.0 mg/L, phenol = 39.49 mg/L and cyanide = 5.2 mg/L was further treated by adsorption process as second stage treatment, and these values were reached to COD = 199.0 mg/L, phenol = 0.0 mg/L and cyanide = 2.36 mg/L. The response surface methodology (RSM) was used for the designing and optimization of the experiments. Analysis of variance (ANOVA) suggested the high regression coefficient R² = 0.999 and 0.993 for COD and phenol removal respectively. The two stage treated CWW can be recycled and reused in same industry for various purpose.     

Catalytic vapor-phase oxidation of 2,2,2-trifluoroethanol

The synthesis of trifluoroacetaldehyde by vapor-phase oxidation of 2,2,2-trifluoroethanol using supported vanadium catalysts was studied. Significant differences were observed in the reaction outcomes resulting from different types of catalysts. The ZrO₂- and Al₂O₃-supported catalyst demonstrated both high catalytic activity and selectivity. The addition of co-catalysts such as MoO₃ or SnO₂ improved catalytic performance (Selectivity: up to 91%; S.T.Y.: >200 g L⁻¹ h⁻¹). The experimental results on catalyst lifetime showed a marked decrease in the activity of the Al₂O₃-supported catalyst within tens of hours, while the ZrO₂-supported catalyst showed little, if any, performance alterations for 2000 h.     

Catalytic properties of spinel-type complex oxides in oxidation reactions

The catalytic activity of M^IM^II ₂O₃ spinel-type complex oxides (M^I = Cu, Ni, Mn, Zn, Mg, Co, M^II = Co, Cr, Al) in the oxidation of CO and ethylbenzene has been investigated. The Co-containing catalysts were more active than the Cr- and Al-containing catalysts. The nature of the cation influenced the catalytic activity. Higher activities were observed for the catalysts containing two transition elements. A correlation between the catalytic and adsorption properties was established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1732, October, 1994.     

Plasmonic osmium hydrosols: Preparation,characterization, and properties

A simple route for the synthesis of mesoporous and plasmonic chitosan supported osmium hydrosols (Os⁰) has been reported using osmium (III)-sodium borohydride redox reaction at room temperature. The composition and morphology of nanoparticles were determined with XRD, XPS, TEM, EDX, SEM, FTIR and N₂-adsorption desorption techniques. No SPR band of Os⁰ at 485 nm was observed for the same redox reaction with cetyltrimethylammonium bromide (CTAB) for ca. 120 min at room temperature. The surface oxidation of Os⁰ into OsO₂ was detected by XRD and XPS. XRD shows the presence of chitosan onto the surface of nanoparticles. The average pore size, and pore volume were found to be 7.23 nm, and 0.239 cc/g, respectively, for Os⁰. The persulfate activation catalytic activity was tested in situ chemical oxidation of basic red 2 (safranin) under activated and un-activated persulfate. Safranin was adsorbed onto the Os⁰ and complex was formed. The oxidation of dye follows pseudo-first order kinetics (k_app = 14.8 × 10^-3 min⁻¹ at [S₂O₈^2-] = 3.3 mM). The activated system showed a much higher dye oxidation rate compared to either S₂O₈^2- or Os⁰ alone. The activation energy (E_a = 105 kJ/mol) was calculated for the system by using Arrhenius equation. The reaction mechanism of Os⁰ activation of persulfate was elucidated and discussed.     

Synthesis of Ni/Al2O3 catalysts via alkaline polyol method and hydrazine reduction method for the partial oxidation of methane

Nickel catalysts supported on γ-Al₂O₃ were synthesized in the presence of polyvinylpyrrolidone (PVP) using both alkaline polyol method and hydrazine reduction method while fixing the weight ratio of [(PVP)]/[Ni(CH₃COO)₂·4H₂O] at 2. The effects of hydrazine [N₂H₅OH]/[Ni] and [NaOH]/[Ni] molar ratios on the structural properties of the catalysts were characterized by transmission electron microscopy (HRTEM) and by X-ray diffraction (XRD). The average of monodispersed Ni nanoparticles ranged between 8.0 and 13.0 nm. The catalytic tests were performed for the partial oxidation of methane in the temperature range of 600–800 °C under a flow rate of 157,500 L kg^–1 hr^–1 with CH₄/O₂= 2. At the molar ratio of [NaOH]/[Ni] = 2, the resultant nickel nanoparticles on alumina was established completely without impurities; thus, it demonstrated the highest catalytic activity, 88% for CH₄ conversion, and H₂ selectivity, 90.60%. The optimum [N₂H₅OH]/[Ni] ratio was determined as 4.1, which means a good catalytic performance and 89.35% selectivity to H₂ for the partial oxidation of methane.     

Catalytic properties of manganites in the oxidation of CO and hydrocarbon

Manganites with a spinel structure MMn₂O₄ (M = Co, Cu, Zn, Mo) and M¹ _0.5M² _0.5 Mn₂O₄ (M = Co, Cu, Zn, Mg) have been synthesized and tested in the catalytic oxidation of CO, C₃H₆, and ethylbenzene. The dependence of the catalytic activity of the manganites on the nature of the cation has been established. The spinels containing transition metal ions (Cu, Co) are more active. A relation between catalytic and adsorption properties of manganites has been established. The participation of the lattice oxygen in the oxidation of CO to CO₂ has been found. The mechanism of the oxidation is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No, 11, pp, 2686–2669. November, 1996.     

Dechlorination of poly(vinyl chloride) using NaOH in ethylene glycol under atmospheric pressure

A solution of NaOH dissolved in ethylene glycol (EG) was effective in the dechlorination of poly(vinyl chloride) (PVC) at atmospheric pressure. The degree of dechlorination increased with increasing temperature, reaching a maximum of 97.8% at 190 °C. The dechlorination proceeded under chemical control and exhibited first-order kinetics with an apparent activation energy of 170 kJ mol⁻¹. The apparent rate constant for dechlorination in 1.0 M NaOH/EG was approximately 150 times greater than that in 1.0 M NaOH/H₂O. In addition, dechlorination was faster at atmospheric pressure in NaOH/EG than under high pressure in NaOH/H₂O. The dechlorination reaction occurs via a combination of E2 and S_N2 mechanisms.