焙烧温度对橄榄石催化甲苯裂解性能的影响

以橄榄石为催化剂,通过N2物理吸附、XRD、H₂-TPR和TEM等手段研究了焙烧温度对催化剂的结构、物相、还原性能以及甲苯裂解反应活性的影响。结果表明,焙烧温度对催化剂结构和活性影响显著,低温焙烧时主要存在Mg₂SiO₄和Fe₂O₃的晶相衍射峰,随着焙烧温度的升高,Fe₂O₃的晶相衍射峰逐渐消失,随之出现了非常明显的 (Fe, Mg)SiO₃的衍射峰。选择适中的焙烧温度可以增加表面上可还原Fe₂O₃的量,从而拥有较高的甲苯裂解活性位。在实验考察范围内,900℃焙烧的橄榄石表现了最高的甲苯裂解活性。TG结果表明,该温度焙烧的橄榄石具有较好的抗积炭性能。     

焙烧温度对Co-Ru-ZrO2/γ-Al2O3F-T合成催化剂性能的影响

采用浸渍法制备钴基催化剂,考察了催化剂焙烧温度对其F-T合成反应性能和产物分布的影响。制备催化剂时,不对催化剂进行焙烧,Co物种容易还原,并可较好分散,催化剂具有较高的催化活性和重质烃选择性。较高温度下焙烧,Co物种和载体间的相互作用增强,形成难还原的铝酸钴化合物,同时氧化钴晶粒聚集或烧结,Co物种的还原程度下降,催化剂CO加氢活性降低,重质烃选择性下降。在原料气n(H₂)∶n(CO)=2.0、483 K、1.5 MPa和800 h^-1条件下,未焙烧、673 K和923 K焙烧的催化剂上进行F-T合成反应,CO的转化率分别为80.27%、78.41%和61.14%,重质烃的选择性C₅⁺分别为88.54%、88.57%和77.95%。较低焙烧温度有利于反应速率的提高和重质烃的合成,较高焙烧温度使CO加氢活性下降,有利于低碳烃的生成。     

Isomerization of n-butane by sulfated zirconia: the effect of calcination temperature and characterization of its surface acidity

The distributions of Brønsted and Lewis acid sites of different acid strengths on sulfated zirconia calcined at 450–650°C were measured by IR of adsorbed pyridine to elucidate the active sites for butane isomerization. The total numbers of Brønsted acid sites were largest when the catalyst was calcined at 500°C. The total numbers of Lewis acid sites increased with increasing calcination temperature to a maximum at 650°C. The catalytic activity in skeletal isomerization of butane correlated well with the number of Brønsted acid sites but not with the number of Lewis acid sites. The active sites were completely blocked by pyridine irreversibly absorbed at 350°C. We suggest that the strong Brønsted acid sites, which are able to retain pyridine against evacuation at 350°C, act as active sites for butane isomerization on sulfated zirconia.     

MoVTeNbO_x催化剂焙烧条件对丙烷氧化制丙烯酸的影响

制备了Mo1V0.25Te0.13Nb0.12Ox催化剂,研究了焙烧条件（焙烧方式、焙烧气氛和焙烧温度）对该催化剂在丙烷选择氧化制丙烯酸反应中的影响。结果表明,两段间歇式焙烧要优于一段式连续焙烧所得催化剂的催化效果,适宜的预焙烧温度既有利于脱除挥发性物质和化学结合水,又能避免活性组分氧化生成不利的晶相;在惰性气氛中焙烧所得催化剂的催化效果要优于在弱氧化性气氛中焙烧,丙烷转化率和丙烯酸收率随着焙烧温度的升高先增加后减小,在600 ℃时达到最大值。     

Effect of calcination temperature on the characteristics of SO<Emphasis Type="Italic">sk</Emphasis>4/2-/TiO<Subscript>2</Subscript> catalysts for the reduction of NO by NH<Subscript>3</Subscript>

The catalytic activity of sulfated titania (ST) calcined at a variety of temperatures has been investigated for selective catalytic reduction (SCR) of NO by NH₃. The NO removal activity of ST catalyst mainly depends on its sulfur content, indicating critical role of sulfur species on the surface of TiO₂. The role of sulfur is mainly the formation of acid sites on the catalyst surface. The presence of both BrØnsted and Lewis acid sites on the surface of sulfated titania has been identified by IR study with the adsorption of NH₃ and pyridine on ST. The reduction of the intensity of IR bands representing BrØsted acid sites is more pronounced than that revealing Lewis acid sites as the calcination temperature increases. It has been further clarified by IR study of ST500 catalyst evacuated at a variety of temperatures. The NO removal activity also decreases with the increase of the catalyst calcination temperature. It simply reveals that BrØnsted acid sites induced by sulfate on the catalyst surface are primarily responsible for the enhancement of catalytic activity of ST catalyst containing sulfur for NO reduction by NH₃.     

煤矸石增钙煅烧的机理

研究了徐州未燃煤矸石以石膏和萤石作矿化剂煅烧前后结构变化及其活化机理.采用X射线衍射和核磁共振测试手段对煤矸石活化过程的物质组成和微观结构进行分析.结果表明:随着Ca与Si的摩尔比和煅烧温度的提高,煤矸石样品的活性也增加.煅烧过程中,硅氧四面体结构从高聚态向低聚态转变,生成多种胶凝性硅酸盐矿物.同时,煅烧前后铝氧结构也发生变化,铝的配位数由6变成4.因此,煅烧激活了煤矸石的硅氧结构,稳定了铝氧结构,有利于煤矸石胶凝活性的改善.     

Surface characterization and catalytic activity of sulfated-hafnia promoted zirconia catalysts for n-butane isomerization

Sulfated-hafnia promoted zirconia containing various compositions of hafnia (1-10 wt.%) were prepared by precipitation method in an attempt to ultimately carry n-butane isomerization reaction. The catalyst samples were calcined under dry air flow at 600 °C. The structural and crystal changes were monitored by FTIR and XRD whereas the textural changes were estimated by low temperature N₂ adsorption. FTIR spectroscopy has been used to characterize the hydroxyl groups and to determine the concentration of Brönsted and Lewis acid sites from pyridine adsorption. The catalytic activity, stability and selectivity of the catalyst samples were tested for n-butane isomerization at 250 °C. The results reveal that the existence of a small content of hafnia increases the surface sulfate density, stabilizes the tetragonal phase of zirconia, increases the amount and strength of Brönsted acid sites and enhances the initial catalytic activity of the samples. Increasing hafnia content to 5 and 10 wt.% is accompanied with the formation of hafnia monoclinic phase which causes a drastic decrease in the amount of Brönsted acid sites and the initial activity of the catalyst. The isomerization of n-butane occurred through bimolecular pathway with the formation of iso-butane, propane and pentanes as primary products. In spite of the high activity of the samples, the catalyst deactivates rapidly during the first hour of the reaction due to coke formation, retreating the catalyst at 450 °C in the presence of dry air before the catalytic reaction lead to regeneration of the initial catalytic activity of the catalyst which implies that the coke formation is the main source for catalyst deactivation.     

Electron spectroscopy of sulfated zirconia, its activity in n-hexane conversion and possible reasons of its deactivation

Sulfated zirconia catalysts were prepared and characterized by X-ray photoelectron spectroscopy taken in the dried state (fresh) and after calcination at 900 K (calc.). A maximum activity was observed as a function of the calcination temperature. The Zr 3d region showed that any Zr hydroxide in the dried catalyst transformed into zirconium oxide upon calcination. The O 1s peak could be fitted by two components corresponding to ZrO₂ and sulfate, respectively. Sulfur was present as sulfate. Both catalysts showed activity in n-hexane conversion (including isomerization) between 300 and 473 K. The activity of the calcined catalyst was much higher. The main products were isopentane and isobutane, along with 2-methyl- and 3-methylpentane. The activity was not stable and only a limited amount of n-hexane transformed before final deactivation. This observation pointed to a limited amount of active sites able to start the reaction. The activity could be fully regenerated by oxygen treatment. Thus, the “oxidative” start of the reaction [ A. Ghenciu, D. Farcasiu, Catal. Lett. 44 (1997) 29] may have also played a role apart from those on strong acid sites. Deactivation may have been due to a partial reduction of sulfate groups rather than to carbon accumulation, as shown also by the minor amounts of S⁴⁺ detected by XPS. Parallel isomerization and splitting of hexane into two C₃ units may occur, followed by the formation of surface C₉ units, the latter being intermediate of larger fragments.     

焙烧温度对Cu-Zn-Al-Mg甲醇合成催化剂结构与性能的影响

采用共沉淀法制备Cu-Zn-Al-Mg甲醇合成催化剂,并用XRD、N2低温吸附、H2-TPR、SEM、TG-DTG等手段对催化剂进行表征,着重考察焙烧温度对催化剂结构与性能的影响.结果表明,随着焙烧温度的增加,铜锌间的相互作用增强,有利于催化反应进行;但过高的焙烧温度又会导致催化剂中CuO晶粒过大,不利于铜的分散.35...     

Effect of calcination behaviors on precipitated iron–manganese Fischer–Tropsch synthesis catalyst

Calcination behaviors play an important role in Fischer–Tropsch (FT) performance over a slurry iron–manganese catalyst. The present study was undertaken to investigate the effects of calcination behaviors (calcination temperature, heating rate and calcination atmosphere) on the textural properties, reduction/carburization behavior, bulk phase structure and FT synthesis performances over precipitated Fe–Mn catalysts. N₂ physisorption, X-ray photoelectron spectroscopy (XPS), H₂ thermal gravimetric analysis (TGA) and M?ssbauer effect spectroscopy (MES) were used to characterize the catalyst. It is found that increasing calcination temperature and heating rate lead to low surface area and high enrichment of Mn on the catalyst surface. High calcination temperature also increased the crystallite size of α-Fe₂O₃ and suppressed the reduction/carburization of the catalysts in H₂ and syngas. Low calcination temperature and low heating rate promoted the further carburization of the catalyst and increased the activity during FT process. High calcination temperature and low heating rate restrained the formation of CH₄, increases C₅⁺ selectivity and improved the selectivity to light olefins. In addition, calcination in argon could improve the carburization and increase FT activity of the catalyst. The present iron–manganese catalyst with lower calcination temperature, lower heating rate and calcined in argon is optimized for its FT performances.     

Structure and Basicity of Mesoporous Materials from Mg/Al/In Layered Double Hydroxides Prepared by Separate Nucleation and Aging Steps Method

This paper presents the synthesis of mesoporous materials from hydrotalcite-like layered double hydroxides (LDHs) with the Mg^{2 +}/(Al^{3 +} + In^{3 +}) molar ratio of 3.0 on the brucite-like lattice and the interlayer carbonate anions, using a novel separate nucleation and aging steps method developed in our laboratory. The physicochemical properties of as-synthesized LDHs and resulting calcined products at 500C were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), ²⁷Al nuclear magnetic resonance (NMR) and low-temperature nitrogen adsorption-desorption experiments. The results indicate calcination of LDHs with a well-crystallized single phase and nanoscale crystallites leads to the formation of the type MgO-like phase, and the pore size distributions of uncalcined and calcined LDHs are mostly in the range of mesopores. Furthermore, calcined materials have higher surface areas, pore volumes, pore diameters and surface basicities than corresponding precursors. When used as solid base catalysts for the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde, the material with higher density of base sites on the surface also exhibited a higher catalytic activity. Particularly, calcined MgAlIn-LDH has highest density of base sites resulting in a highest catalytic activity, as points to an important role of indium as a modifier of the surface properties of solid base catalysts.     

Preparation and stabilization of high specific area zirconia carriers

Zirconia samples have been prepared by precipitation from an aqueous solution of zirconyl nitrate followed by calcination in flowing air at temperatures up to 970 K. The textural properties (S_BET and pore size distribution) of these zirconia powders were very sensitive to the activation procedure. Calcination in carefully controlled conditions at 770 K yielded crystallized zirconia with surface area (S_BET ≈ 130 m² g⁻¹) and porosity suitable for use as a catalyst carrier.

Zirconia samples doped with yttrium, nickel or aluminium were obtained by impregnation of the amorphous hydrous oxide. For solids calcined at 770–970 K, the surface area and thermal stability were improved, but the porosity was lower.     

焙烧温度对共沉淀法制备高温甲烷化催化剂性能的影响

采用共沉淀法制备以Ni为活性组分的Ni-Mg-Al-O高温甲烷化催化剂,考察焙烧温度对催化剂性能的影响。采用N2低温吸附、XRD、H_2-TPR和H_2-化学吸附对催化剂进行表征,并将催化剂用于合成气甲烷化反应。结果表明,焙烧温度高于700℃时,催化剂预还原后织构性能参数变化幅度小。随着焙烧温度的升高,Ni晶粒增大,活性组分与载体之间相互作用增强。焙烧温度700℃时,活性组分分散度最高,催化剂具有优异的低温活性和高温稳定性。     

The calcination temperature after platinum addition and its effect on Pt/WOx–ZrO2 properties

Platinum on tungsten oxide promoted zirconia was prepared using two different platinum precursors: hexachloroplatinic acid and tetraammine platinum nitrate. The catalysts were calcined at different temperatures after platinum addition. The materials were characterized by thermal-programmed reduction, transmission electron microscopy, hydrogen chemisorption at room temperature and they were used for n-hexane isomerization reaction. The calcination temperature after metal addition plays an important role on the catalyst properties. Calcination above 500 °C after platinum addition is not convenient because of the migration of zirconia species over Pt, thus decreasing the hydrogen dissociation capacity of Pt.     

焙烧温度对固相法制备BiYO_3可见光催化剂的影响

以Y_2O_3和Bi_2O_3为原料,采用固相反应制备了BiYO_3可见光催化剂,用热分析、X射线衍射、N_2吸附-脱附、紫外-可见漫反射光谱和拉曼光谱等方法对催化剂进行表征,并以可见光催化降解甲基橙染料废水为探针反应,研究了焙烧温度对BiYO_3的结构及可见光催化活性的影响。研究表明,750℃焙烧的BiYO_3的活性较高,700℃焙烧的催化剂中还存在少量的Bi_2O_3及Y2_O_3,使其光催化活性不高,800℃焙烧的催化剂存在一定的烧结现象,使其比表面积较小,影响其光催化活性。     

Active sites on Pt containing sulfated zirconia

The influence of the Pt and sulfate concentration on the activity of Pt containing sulfated zirconia for n-heptane conversion was investigated. Pt was deposited on the support by impregnation and by photocatalytic deposition. The amount deposited was 2.5 and 0.4 wt% respectively. For comparison a hybrid catalyst consisting of sulfated zirconia and Pt on SiO₂ was prepared. As supports a commercial sulfated zirconia with a fixed sulfate concentration, a commercial and self synthesized Zr(OH)₄ were used. The sulfate content varied between 20 and 60% of a monolayer. The shifts to higher frequency in the IR spectra of CO adsorbed on Pt correlate with the increasing amounts of sulfates on zirconia and are attributable to the changes in the electron density of the supported metal, i.e. the electron deficiency of Pt increases with increasing concentration of acid sites. After activation in air and reduction in hydrogen two SO₂ peaks were detected by a temperature programmed heating procedure (TPE—temperature programmed evolution). The lower the desorption temperature of the first SO₂ peak, the higher the activity. The shift to lower temperature is connected with a higher Pt and sulfate concentration, furthermore with the proximity of the metal to acid sites. The catalysts with a low sulfate concentration possess only Lewis acid sites and are inactive for n-heptane conversion. At higher sulfate concentration, Br?nsted acid sites are present and the catalysts are active. The concentration of these acid sites is related to the concentration of sulfates, which desorb at lower temperature. Dedicated to Professor Konrad Hayek.     

焙烧温度对Au/Fe2O3-ZrO2水煤气变换催化剂的影响

采用共沉淀法制得Au/Fe₂O₃-ZrO₂水煤气变换催化剂。研究了焙烧温度对催化剂的水煤气变换反应性能的影响。并对样品进行了BET、XRD和TPR表征。结果表明，焙烧条件对催化剂的结构和催化活性均有显著影响，焙烧温度越高，催化剂载体结晶度越大，被还原的难度越大，催化剂对低温水煤气变换反应的催化活性越低。Au/α-Fe₂O₃-ZrO₂催化剂的最佳焙烧温度为300 ℃。在此温度下焙烧的催化剂，其载体主相为无定形态，催化活性较好。     

n-Hexane isomerization over copper oxide-promoted sulfated zirconia supported on mesoporous silica

Copper oxide-promoted sulfated zirconia (CuSZ) was supported on MCM-41 by the direct impregnation method. n-Hexane isomerization was investigated over the CuSZ/MCM-41 catalysts. 2-MP, 3-MP and 2,3-DMB are the major isomerization products, besides a small amount of 2,2-DMB. The product distribution is comparable to that reported for Pt based catalysts. The optimal CuO loading in these catalysts calcined at 700 °C is around 3.2 wt% and only leads to the formation of catalytic active metastable tetragonal ZrO₂. The improved performance of CuO-promoted SZ/MCM-41 is a trade-off between the sulfur amount and the content of tetragonal ZrO₂ phase.     

Characterizations of aluminum-promoted sulfated zirconia on mesoporous MCM-41 silica: Butane isomerization

Sulfated zirconia (SZ) was supported on mesoporous molecular sieves MCM-41 by impregnation of zirconium sulfate followed by calcination. The nanochannels of MCM-41 provide a large surface area for the solid state dispersion of zirconium sulfate and a steric restriction on formation of zirconia nanoparticles. The catalysts were tested in n-butane isomerization. With the addition of a proper amount of alumina as a promoter, denoted as ASZ/MCM-41, the catalytic activity was dramatically improved in comparison to the activities of SZ/MCM-41. The increase of activity was determined primarily by the amount of aluminum added and the temperature of calcination. The SZ/MCM-41 catalysts were characterized by X-ray diffraction (XRD), high resolution TEM (HR-TEM), NH₃ adsorption (NH₃-TPD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption (EXAFS). In particular, the Zr K-edge EXAFS data give one a measure of the degree of dispersion of zirconia on the surface of MCM-41. The trend of the promotion effects of alumina on SZ in butane isomerization is not monotonic; there is an optimum level of Al-loading for high activity. It is explained based on three quantitative factors: increased sulfur loadings, balanced distribution of Lewis and Brønsted acid sites, and higher dispersion of zirconia.     

Effect of calcination temperature on the catalytic activity of Au colloids mechanically mixed with TiO2 powder for CO oxidation

In order to elucidate the role of the contact structure between gold and metal oxide support in low-temperature CO oxidation, a mechanical mixture of colloidal gold with TiO₂ powder was prepared and calcined at different temperatures. The sample calcined at 473 K, which is composed of spherical gold particles with a mean diameter of 5.1 nm and TiO₂ powder, is poorly active for CO oxidation at temperatures up to 473 K. The catalytic activity appreciably increases with an increase in calcination temperature up to 873 K even though gold particles grow to larger ones, reaching a level with almost the same turnover frequency as that of Au/TiO₂ prepared by a deposition–precipitation method. This revised version was published online in July 2006 with corrections to the Cover Date.