CO2 Temperature-programmed Desorption Research Articles

Bimetallic Metal-Organic Framework Derived Nanocatalyst for CO2 Fixation through Benzimidazole Formation and Methanation of CO2

In this paper, a bimetallic Metal-Organic Framework (MOF) CoNiBTC was employed as a precursor for the fabrication of bimetallic nanoalloys CoNi@C evenly disseminated in carbon shells. These functional nanomaterials are characterized by powdered X-ray diffraction (PXRD), Fourier Transform Infra-Red spectroscopy (FTIR), surface area porosity analyzer, X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Hydrogen Temperature-Programmed Reduction (H2 TPR), CO2 Temperature-Programmed Desorption (CO2-TPD), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This nanocatalyst was utilized in the synthesis of benzimidazole from o-phenylenediamine in the presence of CO2 and H2 in a good yield of 81%. The catalyst was also efficient in the manufacture of several substituted benzimidazoles with high yield. Due to the existence of a bimetallic nanoalloy of Co and Ni, this catalyst was also employed in the methanation of CO2 with high selectivity (99.7%).

Performance of Modified Alumina-Supported Ruthenium Catalysts in the Reforming of Methane with CO2

Ruthenium (1 wt%) catalysts supported on alumina doped with alkaline (Na and K) and alkaline earth metals (Ba, Ca, and Mg) of different concentrations (1, 5, and 10 wt%) were tested in the dry reforming of methane. All catalysts were prepared by the successive impregnation method. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2, and 2-propanol dehydration. Additionally, catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Stability tests to study coke deposition were performed using long-time dry reforming reactions. All the catalysts showed good catalytic activity, and activity falls were never detected. Ru metallic phase seemed to be resistant to coke formation even though its particles are sintered during a long-term reaction.

Core-Sheath Pt-CeO2/Mesoporous SiO2 Electrospun Nanofibers as Catalysts for the Reverse Water Gas Shift Reaction.

One-dimensional (1D) core-sheath nanofibers, platinum (Pt)-loaded ceria (CeO2) sheath on mesoporous silica (SiO2) core were fabricated, characterized, and used as catalysts for the reverse water gas shift reaction (RWGS). CeO2 nanofibers (NFs) were first prepared by electrospinning (ES), and then Pt nanoparticles were loaded on the CeO2 NFs using two different deposition methods: wet impregnation and solvothermal. A mesoporous SiO2 sheath layer was then deposited by sol-gel process. The phase composition, structural, and morphological properties of synthesized materials were investigated by scanning electron microscope (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), nitrogen adsorption/desorption method, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis, and CO2 temperature programmed desorption (CO2-TPD). The results of these characterization techniques revealed that the core-sheath NFs with a core diameter between 100 and 300 nm and a sheath thickness of about 40-100 nm with a Pt loading of around 0.5 wt.% were successfully obtained. The impregnated catalyst, Pt-CeO2 NF@mesoporous SiO2, showed the best catalytic performance with a CO2 conversion of 8.9% at 350 °C, as compared to the sample prepared by the Solvothermal method. More than 99% selectivity of CO was achieved for all core-sheath NF-catalysts.

Transition metal-containing MgFe ex-LDH mixed oxides, effective catalysts in the hydrodeoxygenation of benzyl alcohol

Several M-MgFe-LDH precursors were prepared via co-precipitation and then calcined at 500 °C to yield the corresponding M-MgFeO mixed oxide catalysts, which were tested in the hydrodeoxygenation (HDO) of benzyl alcohol. The prepared LDH contained Mg and Fe in a mol ratio of 3:1 and 10 at% M with respect to cations, where M = Ni, Co, Ag and Cu. The Cu-MgFeO mixed oxide gave the best results, therefore we proceeded with the preparation of a Cu(x)-MgFeO series, where x = 2.5–20 at% Cu. The prepared solids were characterized by powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed reduction with H2, temperature-programmed desorption of CO2 and energy dispersive X-ray spectroscopy. We studied the influence of the nature of the transition metal M on the activity and selectivity of the catalysts and, for the Cu-containing samples, the influence of Cu loading, reaction time and reaction temperature on their performance in the HDO reaction of benzyl alcohol. With 93.8% conversion and 93.8% selectivity towards toluene at 230 °C, 3 h reaction time and under a hydrogen pressure of 5 atm, the Cu(10)-MgFeO catalyst proved to have the best performance in the studied reaction. Therefore, its stability and reusability were checked. We also proposed a sequence of reactions for the entire HDO process, based on a reverse Mars-van Krevelen mechanism driven by oxygen vacancies formed on the catalyst surface.

Synthesis of the CeO2 Support with a Honeycomb-Lantern-like Structure and Its Application in Dry Reforming of Methane Based on the Surface Spatial Confinement Strategy

Dry reforming of methane has received considerable interest as one of the most efficient thermocatalysis routes to co-convert two greenhouse gases (CO2 and CH4) into syngas (CO and H2), requiring a robust catalyst for extensive application. CeO2 with a honeycomb-lantern-like structure is fabricated by a facile template-free solvothermal process, followed by calcination, and the nickel-active component is confined on the surface of the honeycomb-lantern-like CeO2 support (namely, Ni/CeO2-H) and employed in dry reforming of methane. The catalytic performance of the prepared sample is evaluated in a fixed-bed tubular reactor, and the CH4 and CO2 conversions could reach 83.94 and 82.81% at 800 °C, respectively. Meanwhile, the Ni/CeO2-H catalysts are thoroughly characterized using X-ray diffraction, N2 adsorption–desorption, scanning electron microscopy, H2 temperature-programmed reduction, CO2 temperature-programmed desorption, X-ray photoelectron spectroscopy, thermogravimetric analysis, and CO2 temperature-programmed oxidation (CO2-TPO), and the results demonstrate the enhancing effect of spatial confinement for the honeycomb-lantern-like structure. Moreover, the kinetics studies reveal that Ni/CeO2-H has the lowest activation energy (97.61 kJ/mol) among these Ni/CeO2 catalyst samples, which can facilitate its excellent catalytic performance effectively. Based on the semiempirical power rate equation, the reaction orders of CH4 and CO2 for Ni/CeO2-H are 0.60 and 0.17, respectively. Furthermore, the activation energy of coke gasification for the spent Ni/CeO2-H catalyst is investigated and determined by the CO2-TPO technique on the basis of extrapolating the Wigner–Polanyi equation.

Sr2Fe1.5Mo0.4Ti0.1O6-δ perovskite anode for high-efficiency coal utilization in direct carbon solid oxide fuel cells

Efficient and direct utilization of coal-based fuels is the developmental direction of direct carbon solid oxide fuel cells (DCSOFCs), but their performance is hindered by poor catalytic activity and contaminant poisoning of anode materials. Herein, a Ti-doped double perovskite oxide Sr2Fe1.5Mo0.4Ti0.1O6-δ (SFMT) was developed as the coal-based DCSOFC anode to improve its catalytic activity and resistance to sulfur poisoning. X-ray photoelectron spectroscopy confirms that SFMT shows abundant oxygen vacancy concentration under reducing atmosphere. The as-fabricated DCSOFC with the SFMT anode delivers a maximum power density of 506.5 mW cm−2 at 800 °C when using bituminous coal as the fuel. Electrochemical impedance spectroscopy reveals that Ti doping can effectively promote electrochemical processes on the anode side. Both thermogravimetric analysis and CO temperature-programmed desorption demonstrate that the performance improvement of SFMT is ascribed to its promoted catalytic activity in coal gasification and its increased CO adsorption capacity. The operational period of this coal-based DCSOFC increases from 2 to 10 h after Ti doping, which can be explained by the enhanced structural stability of SFMT under a sulfur-containing environment. Our work may provide some new insight on the design of high-activity anode materials and the understanding of anode reaction mechanisms for coal-based DCSOFCs.

Effect of Zinc on the Structure and Activity of the Cobalt Oxide Catalysts for NO Decomposition

Co4−iZniMnAlOx mixed oxides (i = 0, 0.5 and 1) were prepared by coprecipitation, subsequently modified with potassium (2 or 4 wt.% K), and investigated for direct catalytic NO decomposition, one of the most attractive and challenging NOx abatement processes. The catalysts were characterised by atomic absorption spectroscopy, powder X-ray diffraction, Raman and infrared spectroscopy, temperature-programmed reduction by hydrogen, the temperature-programmed desorption of CO2 and NO, X-ray photoelectron spectroscopy, scanning electron microscopy, the work function, and N2 physisorption. The partial substitution of cobalt increased the specific surface area, decreased the pore sizes, influenced the surface composition, and obtained acid-base properties as a result of the higher availability of medium and strong basic sites. No visible changes in the morphology, crystallite size, and work function were observed upon the cobalt substitution. The conversion of NO increased after the Co substitution, however, the increase in the amount of zinc did not affect the catalytic activity, whereas a higher amount of potassium caused a decrease in the NO conversion. The results obtained, which were predominantly the acid-base characteristics of the catalyst, are in direct correlation with the proposed NO decomposition reaction mechanisms with NOx− as the main reaction intermediates.

Catalytic Oxidation of Glycerol over Pt Supported on MOF-Derived Carbon Nanosheets.

A series of nitrogen-doped porous carbon nanosheets (NPCNs) doped with transition-metal-supported Pt catalysts were prepared by colloidal deposition and evaluated for the selective oxidation of glycerol to glyceric acid (GLYA) under nonalkaline conditions. The transition metal contained in the catalyst was found to affect its performance and selectivity for GLYA, with the Pt/Zr@NPCN catalyst showing the highest catalytic activity and selectivity. These materials were characterized using Brunauer-Emmett-Teller surface area analysis, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and CO2 temperature-programmed desorption. The results showed that the small size of the Pt nanoparticles, the interaction between the Pt nanoparticles and the support, and the unique textural properties of the catalyst all promoted glycerol conversion and GLYA selectivity. A Zr concentration of 1.5 wt % and a support preparation temperature of 800 °C were found to provide a catalyst with the optimal performance that exhibited a glycerol conversion and selectivity for GLYA of 68.62 and 77.29%, respectively, at an initial O2 pressure of 10 bar and 60 °C after 6 h. Even after being recycled five times, this material provided a GLYA selectivity of approximately 75%, although the glycerol conversion decreased from 68 to 50%. The insights may provide new suggestions on the design of efficient support for the selective oxidation of polyols.

CuO decorated vacancy-rich CeO2 nanopencils for highly efficient catalytic NO reduction by CO at low temperature.

With the rapid development of transportation and vehicles, the elimination of NOx and CO has highly attracted public attention. In this work, vacancy-rich CeO2 nanopencil supported CuO catalysts (CuO/CeO2-NPC) were successfully prepared for NO reduction by CO. Importantly, CeO2 with nanopencil-like shape (CeO2-NPC) have been synthesis by solvothermal method for the first time. The physicochemical properties of all samples were studied in detail by combining the means of X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), H2-temperature-programmed reduction (H2-TPR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 physisorption (Brunauer-Emmett-Teller), and NO and CO temperature-programmed desorption (NO-TPD and CO-TPD) techniques. Compared with CeO2 nanorods and nanoparticles supported CuO catalysts (CuO/CeO2-NR and CuO/CeO2-NP), the CuO/CeO2-NPC catalysts showed the highest catalytic activity, affording more than 90% NO conversion at 69°C as well as excellent H2O tolerance at 150°C, which is superior to catalysts previously reported. Characterization results indicated that the synergistic effect between the well-dispersed CuO and the CeO2 nanopencil support enables a favorable electron transfer between these components and enhances the density of surface oxygen vacancies and Cu+ species, which consequently accelerating the redox cycle. The results indicated that the morphology control of CeO2 support could be an efficient way to evidently enhance the catalytic performance for NO + CO reaction.

Layered double hydroxides as precursors for catalysts in Claisen-Schmidt condensation

MMgAlO and MAlO mixed oxides (where M = Cu, Co, Zn and Ni) were obtained by thermal decomposition of the corresponding layered double hydroxides (LDH) precursors and used as catalysts for Claisen-Schmidt condensation of 2’-hydroxyacetophenone and benzaldehyde under solvent-free conditions. The catalysts were characterized by X-ray diffraction (XRD), atomic absorption spectrometry and temperature-programmed desorption of CO2 (TPD-CO2). Gas chromatography – mass spectroscopy (GC/MS) methods were used for the identification and quantification of the product mixture. A 2’-hydroxychalcone and 2-phenyl-2,3-dihydro-4H-chromen-4-one (flavanone) were received as main products. 3-Benzyl-2-phenyl-4H-chromen-4-one (3-benzylflavone) was achieved as a new product.

Catalytic behavior of Mo–Bi–Fe–Co–K–M–O (M=Ce, Gd, CeGd) catalysts for selective oxidation of isobutene

The further improvement of methacrolein (MAL) selectivity from isobutene (IB) oxidation is crucial and challenging. In this study, based on the typical Mo–Bi–Fe–Co–K–O mixed metal oxide, the rare earth element Gd-doped, Ce-doped and CeGd co-doped catalysts were prepared by co-precipitation strategy to increase the selectivity of MAL from 47.9% to 49.8%, 64.2% and 68.6%, respectively. In order to elucidate in-depth the promoting effect of Ce and/or Gd, various characterizations were utilized including X-ray diffraction patterns (XRD), Raman, X-ray fluorescence spectrometry (XRF), X-ray photoelectron spectroscopy (XPS), O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), CO2-temperature programmed desorption (CO2-TPD), IB-temperature programmed desorption (i-C4-TPD) and in-situ IB-Fourier transform infrared spectroscopy (IB-FTIR). Both Ce and Gd finely regulate the bulk and surface structure of the catalyst, thus altering the redox ability, oxygen mobility and storage ability and basicity. Compared with Ce, Gd addition slightly regulates the variation of Co2+/Co3+ redox couples, greatly enhances the interaction among the components on the catalyst, thus only increases the content of surface oxygen species and has little effect on their mobility. While Ce-containing catalyst performs stronger oxygen storage and migration ability, thus leading to the overproduction of surface Odefect species, which are proposed to be the active sites for the production of MAL and COx. The CeGd co-doped catalyst possesses the proper content of surface Odefect species, thus exhibits much higher MAL selectivity. Moreover, the promoting mechanism of Ce and/or Gd over IB oxidation is proposed. Therefore, this work is helpful for understanding the influence of rare earth elements on the structure of mixed metal oxides and the olefin selective oxidation reaction.

Effect of Holmium Oxide Loading on Nickel Catalyst Supported on Yttria-Stabilized Zirconia in Methane Dry Reforming.

The carbon dioxide reforming of methane has attracted attention from researchers owing to its possibility of both mitigating the hazards of reactants and producing useful chemical intermediates. In this framework, the activity of the nickel-based catalysts, supported by yttria-stabilized zirconia and promoted with holmium oxide (Ho2O3), was assessed in carbon dioxide reforming of methane at 800 °C. The catalysts were characterized by N2-physisorption, H2 temperature-programmed reduction, temperature-programmed desorption of CO2, X-ray diffraction, scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) techniques. The effect of holmium oxide weight percent loading (0.0, 1.0, 2.0, 3,0, 4.0, and 5.0 wt %) was examined owing to its impact on the developed catalysts. The optimum loading of Ho2O3 was found to be 4.0 wt %, where the methane and carbon dioxide conversions were 85 and 91%, respectively. The nitrogen adsorption-desorption isotherms specified the mesoporous aspect of the catalysts, while the SEM images displayed a morphology of agglomerated, porous particles. The TEM images of the spent catalyst displayed the formation of multiwalled carbon nanotubes. TGA of the 4.0 wt % of Ho2O3 catalyst, experimented over 7-hour time-on-stream, displayed little weight loss (<14.0 wt %) owing to carbon formation, indicating the good resistance of the catalyst to carbon accumulation due to the enhancing ability of Ho2O3 and its adjustment of the support.

Ce cooperated layered double oxide with enhanced base sites activity for the synthesis of polycarbonate diols

AbstractThe development of highly efficient alkaline catalysts with abundant base sites is of paramount importance for the synthesis of polycarbonate diols (PCDLs). And the application of heterogeneous catalysts is an effective strategy to address the effect of residual catalysts on the quality of PCDLs. Here, Ce cooperated layered double oxide (LDO‐Ce) was used as a catalyst for the preparation of PCDLs via transesterification between dimethyl carbonate (DMC) and 1,4‐butanediol (BDO). CO2 temperature‐programmed desorption (CO2‐TPD) profiles demonstrated that the introduction of Ce led to an increase in strong base sites of LDO‐Ce, thus endowing LDO‐Ce with excellent catalytic performance. Besides, LDO‐Ce possessed satisfactory specific surface area and pore size. A possible catalytic mechanism was proposed to illustrate the transesterification process. The effects of the reaction conditions on the hydroxyl value, yield, and BDO conversion were further investigated in detail. The yield of PCDLs with a hydroxyl value of 112.2 mg KOH/g (corresponding to a number average molecular weight [Mn] of 1000 g/mol) was 92.44% under its optimum reaction conditions (w (catalyst) = 0.5%, n(DMC)/n(BDO) = 1.25, T‐transesterification = 130°C, t‐transesterification = 5 h, T‐polycondensation = 170°C, t‐polycondensation = 4 h, P‐polycondensation = 10 kPa). Moreover, LDO‐Ce was easily removed after the transesterification process (Step 1), ensuring the quality of PCDLs, and it was recycled three times without significant loss of catalytic activity.

Effects of Silica Modification (Mg, Al, Ca, Ti, and Zr) on Supported Cobalt Catalysts for H2-Dependent CO2 Reduction to Metabolic Intermediates.

Serpentinizing hydrothermal systems generate H2 as a reductant and harbor catalysts conducive to geochemical CO2 conversion into reduced carbon compounds that form the core of microbial autotrophic metabolism. This study characterizes mineral catalysts at hydrothermal vents by investigating the interactions between catalytically active cobalt sites and silica-based support materials on H2-dependent CO2 reduction. Heteroatom incorporated (Mg, Al, Ca, Ti, and Zr), ordered mesoporous silicas are applied as model support systems for the cobalt-based catalysts. It is demonstrated that all catalysts surveyed convert CO2 to methane, methanol, carbon monoxide, and low-molecular-weight hydrocarbons at 180 °C and 20 bar, but with different activity and selectivity depending on the support modification. The additional analysis of the condensed product phase reveals the formation of oxygenates such as formate and acetate, which are key intermediates in the ancient acetyl-coenzyme A pathway of carbon metabolism. The Ti-incorporated catalyst yielded the highest concentrations of formate (3.6 mM) and acetate (1.2 mM) in the liquid phase. Chemisorption experiments including H2 temperature-programmed reduction (TPR) and CO2 temperature-programmed desorption (TPD) in agreement with density functional theory (DFT) calculations of the adsorption energy of CO2 suggest metallic cobalt as the preferential adsorption site for CO2 compared to hardly reducible cobalt-metal oxide interface species. The ratios of the respective cobalt species vary depending on the interaction strength with the support materials. The findings reveal robust and biologically relevant catalytic activities of silica-based transition metal minerals in H2-rich CO2 fixation, in line with the idea that autotrophic metabolism emerged at hydrothermal vents.

Low-Temperature NOx Reduction by H2 on Mo-Promoted Pt/ZrO2 Catalysts in Lean Exhaust Gases

AbstractThis article aims to improve the low-temperature H2-deNOxperformance of the active Pt/ZrO2catalyst using MoOxas a promoter. For this purpose, a systematic series of Pt/ZrO2samples were prepared with a Pt content of 0.25 wt% and Mo loads from 0 to 10 wt%. The samples were physico-chemically characterized by means of powder X-ray diffraction, N2physisorption, temperature-programmed desorption of CO and NH3, Raman spectroscopy and diffuse reflectance infrared spectroscopy using NH3as probe molecule, while the H2-deNOxefficiency was investigated in a lean synthetic exhaust. The Pt/ZrO2catalyst with a Mo load of 3 wt% showed the best performance, including H2-deNOxbetween 80 °C and 150 °C, a maximum NOxconversion of 90% and N2selectivity up to 78%. Isolated MoOxspecies predominately present at Mo loads below 4 wt% were found to act as structural promoter by stabilizing the BET surface area, while also providing smaller Pt particles and more active Pt sites, respectively. By contrast, the aggregated Mo oxide moieties found at higher Mo loads exhibit a clearly weaker promotional effect. The structure–activity-selectivity correlations also suggest that the promoter additionally enables a SCR-related mechanistic pathway to be followed, including the spill-over of NHxspecies from the Pt sites to strong Lewis acid sites in the case of highly dispersed MoOxentities followed by reaction with NOx.

Experimental investigation on biodiesel production through simultaneous esterification and transesterification using mixed rare earth catalysts

In this study, biodiesel production through simultaneous esterification and transesterification of palm oil with 10 wt% of oleic acid using the mixed rare earth catalyst was investigated. The mixed rare earth catalysts were prepared via the co-precipitation method. The effects of the precipitating parameters such as temperature, stirring speed and pH on the physicochemical and morphology of the catalysts were studied. All catalysts were thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), fourier transform-infrared spectroscopy (FTIR), N2 adsorption/desorption, CO2 temperature programmed desorption (CO2-TPD) and NH3 temperature programmed desorption. (NH3-TPD). The results indicated that the mixed rare earth catalyst prepared under the precipitation conditions: at pH 9, a stirring of 400 rpm and temperature of 30 °C showed the highest catalytic of 90% FAME content. High surface area of the catalyst, a significant larger amount of Ce and La contents in the catalyst and an appropriate amount of acid and basic sites on the catalyst led to the high catalytic activity. The catalyst could also accelerate the initial reaction rate to achieve the high FAME content of 50% within 30 min.

High activity and stability of nano‐nickel catalyst based on LaNiO3 perovskite for methane bireforming

AbstractIn this study, a nano‐nickel Ni0 catalyst for bireforming of methane was in‐situ synthesized from the sol‐gel fabricating LaNiO3 perovskite. The various physico‐chemical methods such as powder X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), H2 temperature‐programmed reduction (H2‐TPR), scanning electron microscopy (SEM), and CO2 temperature‐programmed desorption (CO2‐TPD) were used for characterization of the obtained samples. The coke accumulation was investigated via the temperature‐programmed oxidation (TPO) method. The results confirmed the formation of both LaNiO3 perovskite structure and a small amount of NiO with high crystallinity. H2‐TPR profiles and XRD patterns showed that the highly dispersed nanocrystals Ni0 on La2O3 catalysts were formed by in‐situ reduction of LaNiO3 at 800°C for as short as 1 hour or more. The crystal sizes of Ni0 and La2O3 crystals are in the range of 17‐18 nm and 18‐19 nm, respectively. The activity of the catalysts was studied in bireforming of methane by the micro‐flow method in a temperature range of 550‐800°C. LaNiO3‐based catalyst showed excellent performance for methane bireforming reaction. Of which, LaNiO3 sample calcined at 800°C for 1.5 hours and reduced at 800°C for 1.5 hours showed the highest activity when it reached the CH4 conversion of 87% and abnormally high CO2 conversion, reaching 97 % at 700°C and approximately 100 % at 800°C with an ideal H2/CO ratio of approximately 2. At 800°C, the activity of the most outstanding catalyst remained stable for 100 hrs thanks to the high sintering resistance of excellent dispersion of Ni in LaNiO3 lattice and high coke tolerance of the catalyst. The catalytic activity remained stable even when the amount of inert γ‐carbon reached 8.58 mgC/gcat.

Conductometric acetic anhydride gas sensors based on S-doped porous ZnO microspheres with enhanced Lewis base interaction

Acetic anhydride is an essential raw material for manufacturing the drug heroin. Its rapid detection using semiconductor sensors has great significance to curb the spread of drugs. However, there are few reports on the design of semiconductor sensors for acetic anhydride, and the sensing mechanism remains unclear. For this reason, the strategy enhancing the Lewis base sites on the ZnO surface via S-doped is proposed in view of the Lewis acid properties of acetic anhydride combined with Lewis acid base theory. The synthesized S-doped porous spherical ZnO (S-ZnO-600) sensor response (312.4) to 100 ppm acetic anhydride is 4.9 times than ZnO-600 (64.1) with a detection limit of 200 ppb. X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR) and the electron localization function (ELF) indicate that S-doped greatly modulates the electronic structure of ZnO through lattice defects. Meanwhile, the increase of Lewis basicity on the ZnO surface through S doping is further confirmed using CO2 temperature programmed desorption (CO2-TPD), the frontier molecular orbital and the charge density difference (CDD). Gas-phase mass spectrometry (GP-MS) combined with DFT further reveals the catalytic degradation of acetic anhydride sensing process.

Role of phase in NiMgAl mixed oxide catalysts for CO2 dry methane reforming (DRM)

Supported Ni catalysts are considered promising for dry methane reforming (DRM) because of their low cost and high activity. However, they suffer from coke formation at elevated reaction temperatures, leading to rapid catalyst deactivation. Here, we developed a synthesis route for highly active and stable nickel-based catalysts for DRM by changing the Mg/Al ratio. Manipulation of the Mg/Al ratio in NiMgAl catalysts induces a change in the phases present, which subsequently leads to enhancement in activity and stability. The highest activity and stability were observed when both spinel and periclase phases were present in the catalysts at Mg/Al ratio of 1.5 (Ni-Mg1.5AlOx). Based on X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR), chemisorption, and UV-Vis-NIR characterizations, as well as CO2 temperature-programmed desorption (TPD), we found that the co-existence of spinel and periclase phases is associated with changes in Ni reducibility, basicity, and the location of Ni2+ species. This work demonstrates how a change in phase in catalysts influences key factors determining activity and stability for the design of active and stable catalysts.

Adsorption of bisphenol A by TiO2-based organic–inorganic hybrid materials

In this study, TiO2-P25 was modified with benzoic acid (BA) and 2-naphthalenecarboxylic acid (NCA), and subsequently used to adsorb bisphenol A (BPA). The relationship between the hydrophobicity of the modified TiO2 and the amount of BPA adsorbed was investigated. The equilibrium adsorption data were analyzed using the Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Harkins–Jura, and Halsey models. Additionally, TiO2 and TixZr(1-x)O2 of high specific surface area were synthesized via the sol-gel and solvothermal methods. The materials were modified using NCA and used to adsorb BPA. The surface properties of the adsorbent were investigated by Brunauer–Emmett–Teller surface area analysis, Barrett–Joyner–Halenda pore size analysis, CO2 temperature-programmed desorption, and CHN elemental analysis. The specific surface area of TixZr(1-x)O2 (252.1– 455.0 m2/g) was higher than that of TiO2 (157.6 m2/g) and the amount of NCA modified onto TixZr(1-x)O2 (1.106– 1.319 mmol/g) was also higher than that of TiO2 (0.405 mmol/g). The amount of NCA modification onto TixZr(1-x)O2 was promoted by surface base points. The maximum amount of BPA adsorbed was 22.4 mg/L, which was 5.86 times that of TiO2-P25, and approximately 90 % of the BPA was removed from a solution having an initial concentration of 100 mg/L.