ABSTRACT
K-doped Mn-Ce solid solution catalysts were synthesized using a combination of coprecipitation and hydrothermal methods, demonstrating excellent performance in benzene oxidation. The catalyst K1Ce5Mn5 exhibited comparable activity to noble metal catalysts, achieving a 90 % benzene conversion at approximately 194 â. Durable tests under dry and moist conditions revealed that the catalyst could maintain its activity for 50 h at 218 â and 236 â, respectively. Characterization results indicated that the catalyst's enhanced activity resulted from the weakened Mn-O bonding caused by the introduction of K+, facilitating the activation of oxygen and its involvement in the reaction. CeOx, the main crystalline phase of Mn-Ce solid solutions, provided abundant oxygen vacancies for capturing and activating oxygen molecules for the weakened Mn-O structures. This conclusion was further supported by partial density of state analysis from density functional theory computations, revealing that the introduction of K+ weakened the orbital hybridization of Mn3d and O2p. Finally, in situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) studies on Ce5Mn5 and K1Ce5Mn5 catalysts suggested that the introduction of K+ promoted the conversion of adsorbed benzene. Furthermore, intermediate products were transformed more rapidly for K1Ce5Mn5 compared to Ce5Mn5.
ABSTRACT
Adsorbents with dual-component active phases have attracted much attention owing to their potential application in synergistic H2S removal. The influence of spatial arrangements of two components within a support matrix on their desulfurization performance was investigated through regulating the mutual arrangements of CuO and MgO on an activated carbon surface. Their spatial locations were found to remarkably affect interfacial interactions, local pH, the conductivity of adsorbents, and electronic structure of copper oxide. A close contact of CuO with the carbon surface led to strong interactions of both components, inhibiting the reduction of CuO and decreasing its reactivity with H2S. On the other hand, a proximity of MgO to the carbon surface increased local pH, promoting the oxidation of H2S into elemental S, instead of sulfates. Cu+ in the copper oxide phase increased the desulfurization performance due to its ability to activate oxygen and to accelerate a lattice diffusion. Enhanced surface conductivity due to the interfacial interactions improved the desulfurization efficiency and favored the formation of elemental S through promoting an electron transfer in redox reactions.
ABSTRACT
In this work, two single-atom catalysts (SACs) with atomically dispersed RuO2 supported on CrO x were successfully synthesized with a simple reduction strategy for the efficient catalytic oxidation of chlorobenzene (CB). With characterizations like Cs-corrected STEM, XPS, H2-TPR, and O2-TPD, the structure-activity relationship is addressed. The noble metal precursor Ru3+ was anchored with different oxygen species and exposed facets based on the physicochemical properties of catalyst supports. Based on the analysis results, the Ru3+ precursor could be mainly anchored into the surface lattice oxygen of Cr2O3-M over high-index facets (223) and adsorbed oxygen of Cr2O3-P over low-index facets (104), where the precursor Ru3+ was all oxidized to RuO2 when being anchored with the oxygen species of Cr2O3-M and Cr2O3-P, respectively according to XPS analysis. There is a stronger metal-support interaction (SMSI) between Ru ions and the surface lattice oxygen of Cr2O3-M, according to H2-TPR and O2-TPD characterizations. Further, the catalytic performance for CB combustion at a high space velocity of 120 000 mL (g-1 h-1) was tested, and 1RuCr2O3-M performed better than 1RuCr2O3-P in both durability and activity. This could be attributed to the SMSI between single-atom Ru and the lattice oxygen of the 1RuCr2O3-M catalyst and the abundant active sites from the exposed high-index facets. The study provided a novel synthesis strategy for Ru-based SACs with SMSI effect, and the good durability of the catalyst (1RuCr2O3-M) extended the great potential for practical application.
ABSTRACT
Cyclic desulfurization-regeneration-denitrification over carbon-based catalysts is a promising technology for SO2 and NOx simultaneous elimination in steel industry. Regeneration is imperative to the long-term operation of the process, while the research is limited. In this work, Ce modified V2O5/AC catalyst (CeVOx/AC) with higher desulfurization and denitrification activity was prepared and the effect of cyclic regeneration was investigated. Results illustrated that the desulfurization and denitrification activity of CeVOx/AC gradually improved with increasing the regeneration cycles at the optimum regeneration temperature of 470 °C in N2. The increasing Ce3+, V5+ and oxygen vacancies, enhanced surface acidity and improved redox ability contributed to the catalytic activity of regenerated catalysts. For desulfurization, more SO2 transformed into H2SO4 rather than to metal sulfates after cyclic regeneration. For denitrification, the improved redox ability accelerated the oxidation of NO to active NO2, bridged nitrites and nitrates, and the enhanced acidity facilitated the NH3 adsorption, further generating more -NH2 and promoting the SCR activity of regenerated samples. The CeVOx/AC with good activity and regenerative stability shows great application potential in steel industry for the simultaneous SO2 and NOx removal.
ABSTRACT
Dissolved oxygen (DO) is the main corrosive substance in the transport process of urban reclaimed water by pipelines, and it can be removed by catalytic reduction. Activated carbon (AC) has been conventionally used as a carrier for catalysts. This paper focuses on the effect of modification conditions of AC on the catalytic performance for DO removal by hydrazine. The catalytic performance of modified AC (MAC) samples by single and combinatory methods has been investigated. The results showed that the combinatory method was better than the single method, and the MAC by combinatory method of high-pressure hydrothermal method followed by metal salt solution impregnation method could remarkably promote the catalytic activity for DO removal. The prepared catalyst GS270-5-Ni-60-3 had the optimal catalytic activity at the conditions of reaction temperature of 30°C, pH 10 and the initial DO concentration of 5.31â mg/L, and the DO removal rate could reach 98.74%. Meanwhile, the samples of AC and MAC were characterized using BET, SEM and FTIR technologies. The experimental results showed that the high-pressure hydrothermal method could significantly improve the pore structure of AC, and the clogging of AC was not obvious by impregnation modification. Furthermore, the surface group of MAC also has a certain influence on the DO removal in reclaimed water.
Subject(s)
Charcoal , Oxygen , Catalysis , Oxidation-Reduction , WaterABSTRACT
In order to transport reclaimed water safely through stainless steel (SS) heat-supply pipeline networks during their idle period, one must understand the degree to which chlorine in reclaimed water is corrosive to SS. In this study, electrochemical methods were used to evaluate the corrosion resistances of two types of SS materials, AISI 304 and AISI 316, in simulated reclaimed water at chloride concentrations of 25 to 400 mg L-1, which are similar to those present in practice. The differences in corrosion resistance between the two types of SS material were investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests (Tafel curves). The passivation layers on the two types of SS exhibited obvious similarities under several experimental conditions. However, EIS, polarization resistance, effective capacitance, Tafel curve, and Scanning Electron Microscope (SEM) data showed that AISI 316 has better corrosion resistance than AISI 304. The corrosion behaviours could be described as a series of reactions between Fe, Cr, and H2O that generate several precipitated products such as Fe2O3, Cr2O3, FeOOH, and CrOOH.
