The leaching of V(V) with PO4 in the speciation analysis of soil

The leaching of V(V) from soil by two phosphate reagents, viz. (NH₄)₂HPO₄ and Na₃PO₄ has been studied. (NH₄)₂HPO₄ (1 M) and Na₃PO₄ (0.01 M) were efficient enough to extract all V(V) species from samples. The results were compared with that extracted by Na₂CO₃. Statistical evaluations show that the proposed method is similar to the established method utilizing Na₂CO₃.The method was applied in the analysis of soil samples from contaminated area of the vanadium mine where many grazing cattle died.Validation of the method was also done by comparing the sum of V(IV) and V(V) and the total vanadium obtained from the samples by an independent method. It was found that the sum of V(V) and V(IV) is in good agreement with the total content of vanadium in all samples after HF-H₂SO₄-HClO₄ digestion. From the results of the investigation, it follows that the use of phosphate fertilizers in V(V)-rich soil may enhance the mobility and availability of V(V) to plants. The plants, in turn, are consumed by animals that may die depending on the level of poisoning.     

Measurement of the surface coverage of V/Al2O3 catalysts by infrared spectroscopy,CO2 chemisorption and ion scattering spectroscopy

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al₂O₃ catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm^?1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO₂ chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO₂ chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO₂ chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO₂.     

Measurement of the surface coverage of V/Al2O3 catalysts by infrared spectroscopy, CO2 chemisorption and ion scattering spectroscopy

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al₂O₃ catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm^–1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO₂ chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO₂ chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO₂ chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO₂.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

球磨时间对浆态床CO甲烷化Ni-Al_2O_3催化剂性能的影响

结合行星式球磨机,采用低温固相法制备Ni-Al_2O_3催化剂,考察了球磨时间对Ni-Al_2O_3催化剂晶相结构(XRD)、还原特征(H2-TPR)、孔道结构(BET)、粒径分布(PSD)、表面形貌(SEM)和浆态床CO甲烷化性能的影响.结果表明,球磨时间为60 min,催化剂(CT-60)平均粒径最小,为141 nm;比表面积最大,为329 m2/g.随球磨时间延长,Ni-Al_2O_3催化剂的甲烷化性能(CO转化率、CH_4选择性和CH_4收率)均先增加后减少.其中,球磨时间为60 min制备的催化剂(CT-60)甲烷化性能最佳,其CO转化率、CH_4选择性和CH_4收率分别达87.9%、8 6.8%和74.3%.结合催化剂表征可知,CT-60优异的性能与其具有较小的颗粒尺寸(141 nm)和较大的比表面积(329 m2·g-1)有很大的关联.即,催化剂颗粒尺寸越小,比表面积越大,其性能越好.     

Ti-Si composite oxide-supported cobalt catalysts for CO2 hydrogenation

In the present work, different silica-based supported cobalt (Co) catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by:(i) facilitating the reduction of Co oxides species which are strongly interacted with support, (ii) preventing the formation of silicate compounds, and (iii) inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.     

Bulk and surface structures of V2O5/ZrO2 catalysts for n-butane oxidative dehydrogenation

The present investigation focuses on the structural properties and reactivity of zirconia-supported vanadium oxide catalysts, prepared by equilibrium adsorption in basic (pH 10) or in acid (pH 2.7) conditions with vanadium content up to 6 wt.% (pH 10) and up to 11.6 wt.% (pH 2.7). The samples, heated at 823 K for 5 h in air, were characterized by X-ray diffraction, Raman spectroscopy and TPR, both as prepared and after leaching with an ammonia solution to remove species not anchored to the zirconia surface. Some representative samples were also tested for the n-butane oxidative dehydrogenation (ODH) reaction. Depending on vanadium content, various vanadium species were identified by Raman spectroscopy that reacted differently on exposure to H₂. At similar loading, the fraction of vanadium in a dispersed state and thus interacting with the support was higher in samples prepared at pH 10 than in those at pH 2.7. Samples prepared at pH 2.7 contained a higher fraction of large polymeric structures in addition to ZrV₂O₇ and V₂O₅.In line with literature data for propane ODH on similar catalysts, our catalytic results suggested that the active sites for the ODH reaction are associated with the V–O–V bonds of the polymeric exposed structures, whereas the Zr–O–V sites favour alkane combustion.     

以类水滑石为前驱体的Cu/Zn/Al/(Zr)/(Y)催化剂制备及其催化CO_2加氢合成甲醇的性能

采用共沉淀法合成了Cu:Zn:Al:Zr:Y原子比分别为2:1:1:0:0、2:1:0.8:0.2:0、2:1:0.8:0:0.2和2:1:0.8:0.1:0.1的Cu/Zn/Al/(Zr)/(Y)类水滑石化合物.将前驱体材料在空气中500°C焙烧后得到复合金属氧化物,并将其用于CO2加氢合成甲醇反应.采用X射线衍射(XRD)、热重(TG)分析、N2吸附、氧化亚氮(N2O)反应吸附、氢气程序升温还原(H2-TPR)和H2/CO2程序升温脱附(H2/CO2-TPD)技术对所制备的样品进行表征.结果表明,Zr和Y的引入使得催化剂BET比表面积大幅增加,金属铜的比表面积和分散度均按以下顺序依次增加:Cu/Zn/AlCu/Zn/Al/ZrCu/Zn/Al/YCu/Zn/Al/Zr/Y,然而,强碱位数目占总碱位数目的比例的变化顺序为:Cu/Zn/AlCu/Zn/Al/YCu/Zn/Al/Zr/YCu/Zn/Al/Zr.活性评价结果揭示CO2转化率取决于金属铜的比表面积,甲醇选择性则随强碱位比例的增加而线性增加.因而,Zr和Y的引入有利于甲醇的合成,Cu/Zn/Al/Zr/Y催化剂上的甲醇收率最高.     

负载型CuO/TiO2催化剂催化CO2加氢制甲醇

采用浸渍法制备了CuO/TiO_2负载型催化剂,并将其用于CO2加氢制甲醇反应。重点考察了铜的负载量对催化剂性能的影响,并对其物化性能和催化性能之间的关系进行了讨论。结果发现,随着铜负载量的增加,催化剂中金属铜的比表面先增加后减小,当铜的负载量为10%(质量百分数)时达到最大值。催化剂的表面碱性位数量随铜含量的增加持续减小,中等碱位和强碱位的强度下降。当铜的负载量不高于10%时,CO2的转化率与铜的比表面积呈线性关系。甲醇选择性与催化剂的表面碱位性质有关,过强的碱性位会降低甲醇选择性。     

负载型CuO/TiO2催化剂催化CO2加氢制甲醇

采用浸渍法制备了CuO/TiO₂负载型催化剂,并将其用于CO₂加氢制甲醇反应。重点考察了铜的负载量对催化剂性能的影响,并对其物化性能和催化性能之间的关系进行了讨论。结果发现,随着铜负载量的增加,催化剂中金属铜的比表面先增加后减小,当铜的负载量为10%（质量百分数）时达到最大值。催化剂的表面碱性位数量随铜含量的增加持续减小,中等碱位和强碱位的强度下降。当铜的负载量不高于10%时,CO₂的转化率与铜的比表面积呈线性关系。甲醇选择性与催化剂的表面碱位性质有关,过强的碱性位会降低甲醇选择性。     

Effect of CO2 adsorbents on the Ni-based dual-function materials for CO2 capturing and in situ methanation

The present work studied the effect of different carbon dioxide (CO₂) adsorbents on Ni-based dual-function materials (DFMs) for the development of carbon capture and on-site utilization in a reactor at isothermal condition. The DFMs containing Ni functioning as a methanation catalyst with various CO₂ adsorbents (i.e., CaO, MgO, K₂CO₃, or Na₂CO₃) were prepared on γ-Al₂O₃ through sequential impregnation. The result indicated that Ni-Na₂CO₃/γ-Al₂O₃ had the highest methanation capacity (i.e., 0.1783 mmol/g) and efficiency (i.e., 71.09%) in the CO₂ adsorption–methanation test. The CO₂ uptake and the subsequent methanation capacity of the Ni-Na₂CO₃/γ-Al₂O₃ increased to more than 24 times and more than 17 times, respectively, compared to Ni/γ-Al₂O₃. The high methanation capacity was correlated to its highest amount of weak basic sites, substantial CO₂ capture capacity and capture/release efficiency, and reactivity to H₂ at a lower temperature, supported by CO₂-TPD, TGA analyses for adsorption or adsorption–desorption at the isothermal condition, and H₂-TPRea, respectively. A continuous cyclic CO₂ adsorption–methanation was performed by using the Ni-Na₂CO₃/γ-Al₂O₃ and Ni-CaO/γ-Al₂O₃, showing that the CO₂ adsorption capacity was stabilized from third cycle onward, whereas the methanation capacity was stabilized at all cycles, indicating the high stability of the DFMs for both CO₂ adsorption and subsequent methanation. This work demonstrated successful synthesis of the Ni-based, low-cost, and stable DFMs with the ability to produce methane via the direct capture of CO₂.     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.     

Characterization of Ru/CeO2-Al2O3 catalysts and their Performance in CO2 Methanation

Ru/Al₂O₃ and Ru/CeO₂-Al₂O₃ samples were used as catalysts in CO₂ methanation. The catalysts were characterized by temperature-programmed reduction (TPR) and X-ray diffraction. The promoting effect of ceria on the cataytic activity of the catalysts under study in CO₂ methanation was observed.     

Catalytic properties of the VO<Subscript><Emphasis Type="Italic">х</Emphasis></Subscript>/Ce<Subscript>0.46</Subscript>Zr<Subscript>0.54</Subscript>O<Subscript>2</Subscript> oxide system in the oxidative dehydrogenation of propane

Ce_0.46Zr_0.54O₂ solid solution prepared using a cellulose template was employed as a carrier for vanadium catalysts of the oxidative dehydrogenation of propane. The properties of VO _х /Ce_0.46Zr_0.54O₂ catalyst (5 wt % vanadium) are compared with the properties of the neat support. The carrier and catalyst are studied by means of BET, SEM, DTA, XRD, and Raman spectroscopy. It is shown that the CeVO₄ phase responsible for the ODH process is formed upon interaction between vanadate ions and cerium ions on the surface of the solid solution. The catalytic properties of the catalyst and the support are studied in the propane oxidation reaction at temperatures of 450 and 500°C with pulse feeding of the reagent. It is found that the complete oxidation of propane occurs on the support with formation of CO₂ and H₂O. Three products (propene, CO₂, and H₂O) form in the presence of the vanadium catalyst. It is suggested that there are two types of catalytic centers on the catalyst’s surface. It is concluded that the centers responsible for the complete oxidation of propane are concentrated mainly on the carrier, while the centers responsible for propane ODH are on the CeVO₄.     

Optimization study by Box-Behnken design (BBD) and mechanistic insight of CO2 methanation over Ru-Fe-Ce/γ-Al2O3 catalyst by in-situ FTIR technique

The utilization of carbon dioxide for methanization reactions in the production of synthetic natural gas (SNG) is of increasing interest in energy-related issues. The use of CO₂ as a raw material in methanization reactions in the formation of SNG is of increasing concern associated with energy problems. The effect of three independent process parameters (calcination temperature, ceria loading and catalyst dosage) and their interactions in terms of conversion of CO₂ was considered by response surface methodology (RSM). Box-Behnken design (BBD) revealed that the optimized parameters were 1000 °C calcination temperature, 85%wt ceria loading and 10 g catalyst dosage, which resulted in 100% conversion of CO₂ and 93.5% of CH₄ formation. Reaction intermediate study by in situ FTIR showed that carboxylate species was the most active species on the catalyst surface. In-situ FTIR experiments revealed a weak CO₂ adsorption, that exist namely as carboxylate species over the trimetallic catalyst. As a result, dissociated hydrogen over ruthenium reacts with surface carbon, leading to *CH, which subsequently hydrogenated to produce *CH₂, *CH₃ and finally to the desired product methane. The use of in situ-FTIR study indicated that the CO₂ methanation mechanism does not involve CO as a reaction intermediate. The more detailed mechanism of CO₂ methanation pathways involved over Ru-Fe-Ce/γ-Al₂O₃ catalyst is discussed in accordance with IR-spectroscopic data. The better catalytic activity and stability over Ru-Fe-Ce (5:10:85)/γ-Al₂O₃ catalyst calcined at 1000 °C showed the presence of moderate basic sites for CO₂ adsorption.     

Synthesis and evaluation of N,O‐doped hypercrosslinked polymers and their performance in CO2 capture

A series of N, O‐doped hypercrosslinked microporous polymers (HCPs) with high surface area and rich microporosity were constructed via facile Friedel‐Crafts alkylation promoted by anhydrous ferric chloride (FeCl₃), which used benzyl alcohol (BA) and 2‐phenylimidazole (PID) as the basic building blocks. The effects of structural composition on the pore properties and gas adsorption properties of prepared HCPs were systematically investigated. The results show that by adjusting the ratio of PID to BA, the Brunauer–Emmett–Teller (BET) specific surface area and pore volume of the prepared HCPs can be controlled, and the BET specific surface area of the polymers range from 732–992 m²/g. Gas uptake experiments indicate that the obtained HCPs exhibit very high CO₂ adsorption capacity up to 3.55 mmol/g at 273 K/1.0 bar. Simultaneously, these N, O‐doped HCPs also show quite high isosteric heat of CO₂ sorption at the low coverage (up to 33 kJ/mol). In addition, the prepared HCPs have excellent selective adsorption performance, and the optimal selective adsorption of CO₂/N₂ is 62. These results demonstrate that these prepared HCPs are potential candidates for applications in CO₂ capture.     

CO2 Capture by Hydroxylated Azine-Based Covalent Organic Frameworks

Covalent organic frameworks (COFs) RIO-13, RIO-12, RIO-11, and RIO-11m were investigated towards their CO₂ capture properties by thermogravimetric analysis at 1 atm and 40 °C. These microporous COFs bear in common the azine backbone composed of hydroxy-benzene moieties but differ in the relative number of hydroxyl groups present in each material. Thus, their sorption capacities were studied as a function of their textural and chemical properties. Their maximum CO₂ uptake values showed a strong correlation with an increasing specific surface area, but that property alone could not fully explain the CO₂ uptake data. Hence, the specific CO₂ uptake, combined with DFT calculations, indicated that the relative number of hydroxyl groups in the COF backbone acts as an adsorption threshold, as the hydroxyl groups were indeed identified as relevant adsorption sites in all the studied COFs. Additionally, the best performing COF was thoroughly investigated, experimentally and theoretically, for its CO₂ capture properties in a variety of CO₂ concentrations and temperatures, and showed excellent isothermal recyclability up to 3 cycles.     

Chitosan Based Scaffolds by Lyophilization and sc.CO2 Assisted Methods for Tissue Engineering Applications

Porous chitosan scaffolds with possible tissue engineering applications were synthesized by using lyophilization and supercritical carbon dioxide (sc.CO₂) drying technique. 1% Chitosan (CS) solution in aq. acetic acid was treated with 37% formaldehyde solution; the resulting hydrogels were subjected to solvent-exchange prior to the final treatment procedures. Their morphology, pore structure, and physical properties were characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the specific surface areas and porosities of scaffolds were determined by using N₂ adsorption. The sc.CO₂ treated scaffolds showed a much greater surface area in comparison to the lyophilized one. Hence, sc.CO₂ treated scaffolds is better for cell proliferation. We further investigated the bioactivity of sc.CO₂ treated scaffolds using simulated body fluid (SBF). The sc.CO₂ assisted chitosan scaffold prepared by using green chemistry approach is highly pure and from a hygienic point of view, it is an ideal material for tissue engineering applications.     

铬助剂对Cu/ZrO_2/CNTs-NH_2催化剂催化CO_2加氢合成甲醇性能的影响

采用并流共沉淀方法制备了一系列不同铬含量的Cu/ZrO2/CNTs-NH2催化剂,在固定床反应器上考察铬对催化剂催化CO2加氢合成甲醇反应性能的影响.当铬含量为1%(w),反应温度为260°C,压力为3.0MPa,原料气组成为V(H2):V(CO2):V(N2)=69:23:8,空速为3600 mL·h-1·g-1时,催化剂的促进效果最显著,甲醇收率达7.78%.氮吸附、粉末X射线衍射(XRD)、氢气程序升温脱附(H2-TPR)、X射线光电子能谱(XPS)、二氧化碳程序升温脱附(CO2-TPD)、差热分析(DTA)以及扫描电子显微镜(SEM)等表征结果表明,随着铬含量的增加,铜颗粒的粒径减小,催化剂的比表面积增大.铬的加入一方面提高了铜的分散性,抑制了ZrO2的相变和活性组分的烧结;另一方面提高了CO2的吸附量并促进CO2由弱吸附向强吸附转化,从而提高甲醇的收率;但是当铬含量大于1%时,催化剂表面Cu、Zr的总含量明显下降,降低了CO2的吸附量并且形成了超强CO2吸附物种,抑制了CO2及其中间产物的转化,从而降低了甲醇收率.     

Valence state of Mo and surface coverage of alumina by molybdenum-oxygen species in MoOx/Al2O3

CO₂ chemisorption, BET surface area and the degree of reduction of Mo(VI) (e/Mo) have been determined in MoO_x/Al₂O₃ samples, reduced with hydrogen at temperatures between 673 and 1173 K. The free alumina surface figures calculated from the surface area and e/Mo values were identical with those obtained from direct CO₂ chemisorption measurements. This identity indicates that all of the oxygen ions of the surface molybdenum-oxygen species block the alumina surface.     

Reaction mechanisms of carbon dioxide methanation

Constant increase of carbon dioxide emissions from anthropogenic activities leads to the search of options for its recycling and utilization. Although recycled CO₂ utilization as a raw material for the production of chemicals and propellants can be challenging, it is the most sustainable way to mitigate its emissions. Among the most promising applications of CO₂ is its catalytic fixation with hydrogen via the methanation reaction to methane. CO₂ methanation, depending on the used catalyst and overall reaction conditions, can proceed through different mechanism or pathways. A literature review on the methanation reaction mechanism shows that CO₂ can be converted to methane either by direct methanation or through the formation of a CO intermediate. This article analyses the proposed reaction mechanisms of CO₂ methanation.