Temperature-programmed desorption of water and ammonia on sulphated zirconia catalysts for measuring their strong acidity and acidity distribution

Temperature-programmed desorption (TPD) of water and ammonia over ZrO₂ and sulphated ZrO₂ prepared by different methods has been investigated for measuring strong acidity and acidity distribution on sulphated zirconia-type solid super-acid catalysts. The TPD of water provides a simple reliable method for this purpose because of the high stability of water molecules under redox conditions     

New Method for the Temperature‐ Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

In this review, a method for the temperature‐programmed desorption (TPD) of ammonia experiment for the characterization of zeolite acidity and its improvement by simultaneous IR measurement and DFT calculation are described. First, various methods of ammonia TPD are explained, since the measurements have been conducted under the concepts of kinetics, equilibrium, or diffusion control. It is however emphasized that the ubiquitous TPD experiment is governed by the equilibrium between ammonia molecules in the gas phase and on the surface. Therefore, a method to measure quantitatively the strength of the acid site (?H upon ammonia desorption) under equilibrium‐controlled conditions is elucidated. Then, a quantitative relationship between ?H and H₀ function is proposed, based on which the acid strength ?H can be converted into the H₀ function. The identification of the desorption peaks and the quantitative measurement of the number of acid sites are then explained. In order to overcome a serious disadvantage of the method (i.e., no information is provided about the structure of acid sites), the simultaneous measurement of IR spectroscopy with ammonia TPD, named IRMS‐TPD (infrared spectroscopy/mass spectrometry–temperature‐programmed desorption), is proposed. Based on this improved measurement, Brønsted and Lewis acid sites were differentiated and the distribution of Brønsted OH was revealed. The acidity characterized by IRMS‐TPD was further supported by the theoretical DFT calculation. Thus, the advanced study of zeolite acidity at the molecular level was made possible. Advantages and disadvantages of the ammonia TPD experiment are discussed, and understanding of the catalytic cracking activity based on the derived acidic profile is explained.     

Measurements of acidic property of zeolites by temperature programmed desorption of ammonia

The overall view of the TPD of ammonia to measure the acidic property of zeolites is described. The desorption peaks were identified and the significance of readsorption of ammonia was pointed out for the first time. This part of the work was done using reference catalysts of the Catalysis Society of Japan. The theoretical equation for the TPD with free readsorption of ammonia was then derived. Two methods for determining the strength of zeolite acidity based on the derived equation were proposed. A curve fitting method was then proposed to determine the zeolite acidity; based on this method, not only the strength of acidity but also its distribution could be determined. This method was applied to mordenite and ZSM-5 zeolites with different contents of Al and Na cations, and a simple conclusion was reached; namely, the strength of the acidity was not influenced by the number of acid sites but by the structure of the zeolite. Finally, water vapor treatment to rub out the l-peak (lower temperature peak) was briefly mentioned. This method was applied to precisely determine the acidity of Y-zeolite. A case study about the beta zeolite as the catalyst for the amination of phenol was exemplified; the catalytic activity was discussed in terms of the measured acidity.     

Effect of Acidity of the Surface on the Activity of Rhodium Promoted Zirconium Oxide Catalysts in the Reduction of NO by Hydrocarbons

The acidity of the surfaces of rhodium promoted zirconium oxide catalysts (Rh-Cr₂O₃/ZrO₂ and Rh-CeO₂/ZrO₂) has been investigated by the thermally programmed desorption of ammonia (TPDA) method and IR spectroscopy. A correlation between the acid properties of the surfaces of the catalysts (strength and type of acid centers, presence of Brönsted acid centers) and their activity in the SCR process for the reduction of NO with a propane–butane mixture and propene has been established.     

Heats of Adsorption of Ammonia and Correlation of Activity and Acidity in Heterogeneous Catalysis

Adsorption microcalorimetry was applied to determine heats of adsorption of ammonia on zeolites Y, mordenite, ZSM-5, heteropolyacid H₃PW₁₂O₄₀, as well as silica gel and amorphous aluminosilicates. The plots of differential heats against coverage served to construct the acidity spectra and, in this way, to determine the number of acid sites with different acidity strengths. The behavior of these materials in acid-catalyzed reactions, primarily, in the transformations of hydrocarbons is discussed. Evidence is presented that heats of adsorption of ammonia can be used to obtain correlation plots that describe relations between acidic and catalytic properties of zeolite catalysts.     

High catalytic activity of V2O5-ZrO2 modified with H2SO4 for propene partial oxidation

For V₂O₅–ZrO₂ catalysts, up to 10 mol% the crystalline structure of V₂O₅ was not observed, indicating a good dispersity the surface of ZrO₂. V₂O₅–ZrO₂ catalyst modified with H₂SO₄ exhibited much on higher catalytic activity for propene partial oxidation than unmodified catalysts due to the increased acidity and acid strength of modified catalyst.     

Role of Bifunctionality of ZrO2-Based Oxide Systems in NO Reduction with Lower Hydrocarbons

The catalytic properties of transition metal oxides (Cr, Ce, and Co) supported on ZrO₂ synthesized by various methods, as well as the effect of rhodium on the performance of the e O _y /ZrO₂ oxide systems in NO reduction with hydrocarbons (methane, propane–butane mixture, and propene) were studied. The acidity of the surface of the catalysts was studied by IR spectroscopy and ammonia temperature-programmed desorption. The adsorption of NO, propene, and their mixture on the Rh–r₂₃/ZrO₂ and Rh–O₂/ZrO₂ catalysts at temperatures of 293–623 K was studied by IR spectroscopy. The adsorption and co-adsorption of the reactants was found to differ significantly depending on the nature of the surface. The activity of the catalysts studied in NO selective catalytic reduction with hydrocarbons is due to the presence of the acidic functional groups on their surface.     

碱土金属氧化物改性ZrO2催化1,4-丁二醇选择性脱水合成3-丁烯-1-醇

采用浸渍法制备了碱土金属氧化物CaO,SrO或BaO改性的ZrO₂酸碱双功能催化剂,借助X射线衍射、低温N₂物理吸附、NH₃和CO₂程序升温脱附等手段表征了催化剂的结构、织构以及表面酸碱性质,并考察了其催化1,4-丁二醇选择性脱水合成3-丁烯-1-醇的反应性能.结果表明,碱土金属氧化物的引入显著调变了催化剂表面的酸性和碱性中心,进而对1,4-丁二醇转化率和3-丁烯-1-醇选择性产生重要影响.其中,CaO改性的ZrO₂样品中形成了大量的Ca-O-Zr结构,在ZrO₂表面形成大量碱性位点的同时,保持了较高的酸密度;而SrO和BaO改性的样品中生成了相应的锆酸盐,ZrO₂表面的酸密度呈现不同程度的下降.因此,CaO/ZrO₂催化剂表现出最优的催化活性和3-丁烯-1-醇选择性,350℃时,3-丁烯-1-醇收率最高,达60.5%.催化剂表面的酸碱协同作用是选择性合成3-丁烯-1-醇的关键因素.     

Effect of Bismuth Additives on the Properties of Vanadium–Phosphorus Oxide Catalyst in the Partial Oxidation of n-Pentane

The selective oxidation of n-pentane on vanadium–phosphorus oxide (VPO) catalysts with bismuth additives (Bi/V = 0–0.30) is studied. The catalysts are characterized by XRD, XPS, and specific surface area measurements using nitrogen adsorption. Their acidic properties are studied (using ammonia TPD and the 2-methyl-3-butyn-2-ol reaction). It was found that the introduction of bismuth insignificantly affects the specific surface area but increases the surface concentration of phosphorus and changes the acidic properties of the catalysts. The specific catalytic activity of samples in n-pentane oxidation correlates with the effective charge of surface oxygen (E _b of O1s electrons). The selectivity to citraconic anhydride increases with an increase in the general surface acidity. The selectivity to maleic anhydride increases with an increase in the Brønsted acidity of the surface. The selectivity to phthalic anhydride increases with an increase in the Lewis acidity. The pathways of product formation in the partial oxidation of n-pentane are proposed.     

Trimerization of Isobutene Over Solid Acid Catalysts

Oligomerization of isobutene is a very promising reaction not only for the production of isobutene oligomers such as trimers but also for the separation of isobutene from C₄ mixtures. Several solid acid catalysts have been applied for the continuous oligomerization of isobutene in liquid phase. This review analyzes the trimerization of isobutene over various solid acid catalysts such as zeolites, oxides (zirconias and titanias) and acid resins. Trimers selectivity increases with increasing isobutene conversion, irrespective of catalysts such as zeolites and acid resins. Very stable operation with high trimers selectivity is accomplished with WO _x /ZrO₂ catalyst having tetragonal zirconia or various zeolite catalysts with high Lewis acid site-to-Brønsted acid site ratio (LA/BA ratio). For a good performance, acid resins should be macroporous and strong acid (sulphonic acid group) with high acid concentration. Inorganic catalysts are superior to acid resins because the deactivated inorganic materials can be regenerated by simple calcination. The WO _x /ZrO₂ catalyst may be applied to a commercial process because about several thousand tons of isobutene can be oligomerized per one ton of zirconia catalyst in a catalytic cycle without regeneration. The oligomerization of isobutene may be improved further because the reaction has been started only recently and no research has been done for the optimization of the reaction and catalysts. It is expected to develop a new inorganic catalyst having suitable acidity, LA/BA ratio and phase, etc. by further research. The isobutene trimers, with or without hydrogenation, may be used for various purposes, and the importance of this trimerization reaction will be increased considering the expected surplus of isobutene due to the banned use of methyl-tert-butyl ether.     

Correlation between acidic properties of nickel catalysts and catalytic activities for ethylene dimerization and butene isomerization

Catalytic activities of NiO–SiO₂ for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of NiO–SiO₂ catalysts. Catalytic activities of NiO–TiO₂ catalysts modified with H₂SO₄, H₃PO₄, H₃BO₃, and H₂SeO₄ for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO–TiO₂/SO₄^2- >> NiO–TiO₂/PO₄^3-NiO–TiO₂/BO₃^3- > NiO–TiO₂/SeO₄^2-> NiO–TiO₂, showing clear dependence of catalytic activity upon acid strength. The high catalytic activity of supported nickel sulfate for ethylene dimerization was related to the increase of acidity and acid strength due to the addition of NiSO₄. The asymmetric stretching frequency of the S=O bonds for supported NiSO₄ catalysts was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. For NiSO₄/Al₂O₃–ZrO₂ catalyst, the addition of Al₂O₃ up to 5 mol% enhanced catalytic activity for ethylene dimerzation and strong acidity gradually due to the formation of Al–O–Zr bond. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni⁺, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO₄/ -Al₂O₃ and Ni 2p XPS.     

Selective catalytic oxidation of ammonia into nitrogen and water vapour over transition metals modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript>

Copper or iron supported on commercially available oxides, such as γ-Al₂O₃, TiO₂ (anatase) and monoclinic tetragonal ZrO₂ (mt-ZrO₂) were tested as catalysts for selective catalytic oxidation of ammonia into nitrogen and water vapour (NH₃-SCO) in the low temperature range. Different commercial oxides were used in this study to determine the influence of the specific surface area, acidic nature of the support and crystalline phases as well as of the type of species and aggregation state of transition metals on the catalytic performance in selective ammonia oxidation. Copper modified oxide supports were found to be more active and selective to nitrogen than catalysts impregnated with iron. Activities of both transition metal modified samples decreased in the following order: mt-ZrO₂, TiO₂ (anatase), γ-Al₂O₃. Quantitative total ammonia conversion was achieved with the Cu/ZrO₂ catalytic system at 400°C. Characterisation techniques, e.g. H₂-temperature programmed reduction, UV-VIS-diffuse reflectance spectroscopy, suggest that easily reducible copper oxide species are important in achieving high catalytic performances at low temperatures.     

Mechanism of the Effect of Thermal Treatment on the Formation of Strong Acid Sites in the Surface Layers of Sulfated Metal Oxides

Strong acid catalysts were synthesized by the impregnation of hydrated ZrO₂ and TiO₂ with sulfuric acid followed by thermal treatment at different temperatures. The surface acidity and crystallochemical characteristics of the catalysts were studied by potentiometry and X-ray diffraction analysis, respectively. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 350 to 600°C for SO^2– ₄/ZrO₂ or to 200°C for SO^2– ₄/TiO₂; this increase correlated with the degrees of crystallinity of the samples. A hypothesis was proposed to explain the gradual accumulation of acid sites in the surface layer in the course of thermal treatment. It was assumed that, because of crystallographic changes that caused the weakening or even rupture of Zr–O–S and Ti–O–S bonds in modified surface layers, these layers exhibited an enhanced reactivity in contact with water vapor. Subsequently, this resulted in the formation of strongly acidic grafted M–O–SO₃–H⁺ groups.     

Catalytic Performances of Binder-free ZSM-5 Catalysts for Dehydration of Crude Methanol to Dimethyl Ether

A series of binder‐free ZSM‐5 catalysts and a binder‐containing catalyst were prepared and characterized with X‐ray diffraction (XRD), X‐ray fluorescence (XRF), ²⁷Al magic‐angle spinning (MAS) nuclear magnetic resonance (NMR), N₂ sorption and ammonia temperature‐programmed deposition (TPD) methods. The catalytic activity and selectivity in the dehydration of crude methanol to dimethyl ether (DME) were evaluated in a fixed‐bed reactor for the catalysts. The outstanding structural characters such as high zeolite contents, sufficiently open channels and richness in mesopores have been proved on these binder‐free catalysts. The influence of the solid‐acidity, which is closely related to the framework silica alumina ratio (SAR) of the catalysts, on the catalytic properties has been discussed. A binder‐free catalyst with a better potential in application has been selected for its high activity and selectivity, long life‐time and non‐sensitivity to water contents in the feed. The reason for its excellent performance of the catalyst was discussed.     

Zr 改性MnOx/MWCNTs催化剂的结构特征与低温SCR活性

以ZrO（NO₃）₂·2H₂O为前驱体对多壁碳纳米管（MWCNTs）进行了改性并负载MnO_x制备了MnO_x/ZrO₂/MWCNTs 催化剂. 考察了Zr 对催化剂低温选择性催化还原（SCR）反应活性的影响,并通过多种分析手段对催化剂的结构进行了表征. 结果表明Zr 的添加对催化剂的低温SCR活性具有显著的促进作用,当Zr 负载量为30%时,催化剂活性最佳. X射线衍射（XRD）、拉曼（Raman）光谱、透射电镜（TEM）、N₂吸附-脱附的表征结果分析表明,适量的Zr 改性促进了MnO_x在载体表面的分散,增强金属氧化物与MWCNTs 之间的作用,也能增加催化剂的比表面积、孔容和孔径. X 射线光电子能谱（XPS）、H₂程序升温还原（H₂-TPR）和NH₃程序升温脱附（NH₃-TPD）的分析结果则显示,Zr 能提高催化剂表面化学吸附氧浓度,促进Mn³⁺转化为Mn⁴⁺,从而使催化剂表面的活性位点增多,氧化还原能力增强,同时还提高了催化剂表面酸性位点的数量和强度,促进了NH₃的吸附,是MnO_x/ZrO₂/MWCNTs 催化剂低温SCR活性提高的主要原因.     

Combustion of Carbon Black Catalyzed by Transition Metal-Promoted Y2O3–CeO2–ZrO2 Solid Solutions1

The activity of M-free and M-loaded 10YO_1.5–10CeO₂–80ZrO₂ solid solution (M = Cu, V, or W) towards carbon black combustion was studied using TG/DTA and TPO techniques. It was demonstrated that all studied catalysts lower the temperature of carbon black combustion. The selectivity of the catalytic reaction in CO₂ formation was 100%. It was evidenced that the fast oxidation of carbon at lower temperatures, observed only in the TG/DTA apparatus, was due to heat- and mass-transfer limitations, resulting in a runaway reaction. Using TPR technique, it was shown that, in the temperature range of DTA curve, oxygen on the catalyst surface was rather reactive (and, therefore, it could be easily released by support for the oxidation of carbon), whereas the reactivity of bulk oxygen was negligible. The activity of the metal-loaded 10YO_1.5–10CeO₂–80ZrO₂ (Y-10) samples varied according to the following sequence: Cu/Y-10 > V/Y-10 > W/Y-10. For Cu- and V-containing catalysts, a contribution of a surface redox mechanism in reaction was proposed by comparing EPR spectra of pure catalysts with those of the samples (catalysts mixed with carbon black) after catalysis.     

Direct Decomposition of Nitrogen(I) Oxide on Iron-Containing Zeolite,Zirconium Oxide,and Mixed Catalysts

As a result of testing a series of catalysts based on iron-containing zeolites of different structural types (Y, M, pentasil), zirconium dioxide, and a binary support (zeolite + ZrO₂) in the reaction of direct decomposition of nitrogen(I) oxide, we have shown that the most active zeolite-based catalysts are characterized by the presence of strong acid sites on the surface.     

ZrO2?SiO2 mixed oxides as supports for platinum catalysts

Mixed ZrO₂–SiO₂ oxides were prepared by the sol-gel method and used as supports for platinum catalysts. Activity tests show that Pt/ZrO₂–SiO₂ catalysts can be used in the aromatization of n-heptane.     

Preparation of ZrO2-TiO2-CeO2 and Its Application in the Selective Catalytic Reduction of NO with NH3

TiO₂,ZrO₂-TiO₂,andZrO₂-TiO₂-CeO₂ were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), specific surface area measurements (BET), temperature programmed desorption (NH₃-TPD), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results showed that ZrO₂-TiO₂-CeO₂ exhibited large number of surface strong acid, possessed some oxygen storage capacity, and strong redox property. The three materials were used as supports and the monolith catalysts were prepared with 1% (w) V₂O₅ and 9% (w)WO₃ for selective catalytic reduction (SCR) of NO with ammonia in the presence of excessive O₂, and the results of catalytic activity showed that the catalyst used ZrO₂-TiO₂-CeO₂ as support yielded nearly 100% NO conversion at 275 °C at a gas hourly space velocity (GHSV) of 10000 h⁻¹, and it had the best catalytic activity and showed great potential for practical application.     

Highly active and reusable heterogeneous catalysts for acylation of anisole

In the present study, non-conventional solid acid catalysts such as NaY, metal ion exchanged zeolite NaY (Zn²⁺, Fe³⁺, Ce³⁺, La³⁺ and Nd³⁺), H-mordenite, H-β and HZSM-5 were used in order to overcome the disadvantages of conventional Friedel-Crafts catalysts for the acylation of anisole with acetic anhydride. Among the various zeolites studied, the HY zeolite shows an intermediate activity. Zeolite containing transition metal ions (Zn²⁺ and Fe³⁺) are less active and zeolite NaY is nearly inactive. The catalysts exhibit the activity in the order H-β>transition metal ions (Zn²⁺ and Fe³⁺)>HY>NaY zeolite. The highest catalytic activity of H-β could be due to its larger pore size. The type of acidity and the acid strength in zeolite Y were determined by FTIR and differential scanning calorimetric (DSC) studies on the pyridine adsorbed catalysts. The correlation of catalytic activity with acidity reveals that Brönsted acid sites in zeolite promote the acylation of anisole.