Methanol to Gasoline over ZSM-5 Zeolite Treated with Alkaline Mixture with Different Ratios of TBA<Superscript>+</Superscript>/OH<Superscript>–</Superscript>

The influence of ZSM-5 (SiO₂/Al₂O₃ = 50) treatment with a tetrabutylamine hydroxide (TBAOH)/NaOH mixture having different mole ratios on its physicochemical properties and catalytic performance in the reaction of methanol to gasoline (MTG) was investigated. It was found that, with increasing ratio TBA⁺/OH^–, the crystallinities, micropore surface areas, micropore volumes, the amounts of strong acid sites and Brönsted acid sites gradually increased, and the mesopore volumes decreased. The treatment with pure TBAOH (TBA⁺/OH^– = 1.0) ensured the formation of narrow and uniform intracrystalline mesoporosity and the large amounts of strong or Brönsted acid sites on the zeolite, which contribute to the highest liquid hydrocarbon yield in the reaction of MTG.     

Approach to De-NOx-ing photocatalysis. II excited state of copper ions supported on silica and photocatalytic activity for no decomposition

Cu²⁺ ions supported on SiO₂ (Cm²⁺ /SiO₂) prepared by an ion-exchange method are reduced to Cu⁺ when Cu²⁺/SiO₂ samples are evacuated at temperatures higher than 573 K Reduced Cu²⁺ ions on SiO₂ (Cu⁺/SiO₂ catalyst) decomposes NO molecules photocatalytically and stoichiometrically into N₂ and O₂ at 275 K. The physicochemical and photochemical properties of copper ions anchored onto SiO₂ have been investigated by means of ESR and dynamic photoluminescence spectroscopies, as well as the analysis of photoreaction products. These results indicate that the excited state of the copper ions (Cu⁺ species) plays a significant role in the photocatalytic decomposition of NO molecules and the photoreaction involves an electron transfer from the excited state of the Cu⁺ ion into an anti-bonding π orbital of NO molecule within the lifetime of its excited state. Thus, the present results obtained with the Cu⁺/SiO₂ catalysts imply the possibility of their utilization as a potentially promising type of photocatalysts in gas-solid systems.     

Hydrothermal ethanol conversion on Ag,Cu, Au/TiO2

The effect UV irradiation and silver, copper, and gold ions (M ^z+) supported on titania (anatase) have on the activity of M/TiO₂ samples in ethanol conversion at 150–400°C is examined. After UV irradiation, the yields of acetaldehyde and ethylene increase for TiO₂ and Ag/TiO₂ samples, while the activity of Cu²⁺/TiO₂ decreases. The activation energy of ethanol dehydration declines in the order TiO₂ > Au³⁺ > Cu²⁺ > Ag⁺ and correlates linearly with a reduction in the radius of M ^z+ in crystal. The number of acidic sites on a M/TiO₂ surface titrated via pyridine adsorption grows upon the introduction of M. Unlike Cu²⁺/TiO₂, these sites are not activated after the irradiation of TiO₂, Ag⁺/TiO₂, and Au³⁺/TiO₂. According to IR spectral data on adsorbed pyridine, all samples contain Lewis and Brönsted acidic sites.     

Surface acidity of supported vanadia catalysts

The surface acidity of SiO₂, γ-Al₂O₃ and TiO₂ supported vanadia catalysts has been studied by the microcalorimetry and infrared spectroscopy using ammonia as the probe molecule. The acidity in terms of nature, number and strength was correlated with surface structures of vanadia species in the catalysts, characterized by X-ray diffraction and UV-Vis spectroscopy. It was found that the dispersion and surface structure of vanadia species depend on the nature of supports and loading and affect strongly the surface acidity. On SiO₂, vanadium species is usually in the form of polycrystalline V₂O₅ even for the catalyst with low loading (3%) and these V₂O₅ crystallites exhibit similar amount of Brönsted and Lewis acid sites. The 25%V₂O₅/SiO₂ catalyst possesses substantial amount of V₂O₅ crystallites on the surface with the initial heat of 105 kJ mol^-1 and coverage of about 600 mmol g^-1 for ammonia adsorption. Vanadia can be well dispersed on g-Al₂O₃and TiO₂ to form isolated tetrahedral species and polymeric two-dimensional network. Addition of vanadia on γ-Al₂O₃ results in the change of acidity from that associated with g-Al₂O₃ (mainly Lewis sites) to that associated with vanadia (mainly Brönsted sites) and leads to the decreased acid strength. The 3%V₂O₅/TiO₂ catalyst may have the vanadia structure of incomplete polymeric two-dimensional network that possesses the Ti-O-V-OH groups at edges showing strong Brönsted acidity with the initial heat of about 140 kJ mol^-1 for ammonia adsorption. On the other hand, the 10%V₂O₅/TiO₂ catalyst may have well defined polymeric two-dimensional vanadia network, possessing V-O-V-OH groups that exhibit rather weak Brönsted acidity with the heat of 90 kJ mol^-1 for NH₃ adsorption. V₂O₅ crystallites are formed on the 25%V₂O₅/TiO₂ catalyst, which exhibit the acid properties similar to those for 25%V₂O₅ on SiO₂ and γ-Al₂O₃.     

Activity of palladium sulfide catalysts in the reaction of gas-phase hydrogenation of 2-methylthiophene

In the interaction of hydrogen with 2-methylthiophene in the gas phase over palladium sulfide catalysts at 180–260?C and 0.1–0.8 MPa, the saturation of the thiophene ring resulting in 2-methylthiolane and the hydrogenolysis of 2-methylthiophene occurs. When the conversion is lower than 60%, these reactions occur independently; at higher conversions, methylthiolane also undergoes hydrogenolysis. The specific catalytic activity of PdS supported on γ-Al₂O₃, TiO₂, and carbon and without support is much lower in the hydrogenation of 2-methylthiophene than the activity of PdS supported on SiO₂, aluminosilicate, and zeolite HNaY having strong Brönsted acid surface sites.     

HZSM-35分子筛酸性质对甲缩醛和乙酸甲酯羟醛缩合反应的影响

丙烯酸及其酯是重要的化工原料,广泛应用于涂料、粘结剂、纤维等领域,目前工业上常采用丙烯两段氧化法进行制备,但该法以石油基原料丙烯为源头,采用V/Mo/Bi等金属催化剂,不符合可持续发展理念,且存在环境污染及氧气下产物易过度氧化等问题.如何高效、安全、大规模工业化制备丙烯酸及其酯是研究者追求的目标.以乙酸甲酯(Mac)和甲醛为原料,通过羟醛缩合一步制备丙烯酸及其酯是一条完全不同于丙烯氧化法的合成路径,原料均可由煤基甲醇得到,符合我国"富煤、贫油、少气"基本能源结构,且该方法碳原子利用率为100％,副产物仅为水,属于绿色环保合成路径.本文以甲缩醛(DMM)为甲醛源,创新性地采用固体硅铝分子筛为酸性催化剂,催化DMM和MAc发生羟醛缩合反应来制备丙烯酸.硅铝分子筛具有较高的活性,可高效地催化羟醛缩合反应,且具有很好的再生性能,即使催化剂寿命较短,也可采用流化床或移动床等反应器进行工业化,因此具有良好的工业化前景.硅铝分子筛中常含有Br?nsted酸和Lewis酸,为试图说明羟醛缩合反应的真正活性位点,我们以羟醛缩合反应性能最佳的HZSM-35分子筛为研究目标.首先,利用红外研究HZSM-35分子筛的酸性质.发现分子筛中桥羟基提供Br?nsted酸,外骨架铝物种提供Lewis酸.通过对桥羟基红外峰一阶求导,发现其对称性较差,表明Br?nsted酸在HZSM-35分子筛孔道中分布不均匀.利用红外分峰手段,得知约51％的Br?nsted酸分布于八元环和六元环交叉所形成的笼(cage)中,约23％分布于十元环孔道,26％分布于八元环孔道中.同时,利用吡啶在分子筛HZSM-35不同温度下的吸附情况验证了这一分峰结果.其次,利用钠离子交换方法制备不同Br?nsted酸浓度的ZSM-35分子筛,经吡啶红外表征得知,Br?nsted酸浓度随钠离子交换程度增加而逐渐降低,而Lewis酸浓度并未改变;在羟醛缩合反应性能中,丙烯酸及丙烯酸甲酯选择性和收率均随Br?nsted酸浓度增加而逐渐升高,考虑到Lewis酸浓度并未变化,可知Br?nsted酸是羟醛缩合反应性能的活性位点,其浓度增加有利于羟醛缩合反应性能的提高.同时,对比不同ZSM-35分子筛失活现象,高Br?nsted酸浓度时分子筛重积炭量最高,这可能是由于Br?nsted催化不饱和产物关环生成芳烃物种或(和)发生氢转移过程所导致.     

Acid properties of semicrystalline zeolitic mesoporous UL-ZSM-5 materials

UL-ZSM-5 materials have been prepared by templated solid-state crystallization of zeolites starting from the amorphous mesostructured aluminosilicate Al-Meso. Microcalorimetry and FTIR have been employed to characterize their surface acidity. In good agreement with ²⁷Al MAS NMR data, UL-ZSM-5 displayed an improved density and strength of Brönsted acid sites, as compared to Al-Meso, owing to the incorporation of aluminium in a tetrahedral environment similar to that of zeolite ZSM-5. Moreover, they showed an enhanced Brönsted/Lewis relative acid ratio. However, Al-Meso showed the highest concentration of strong Lewis acid sites due to its largest amount of aluminium in extraframework positions.     

Base-induced Brönsted Acid Sites on Dealuminated HY Zeolite: A Solid-state NMR Spectroscopy Study

Using trimethylphosphine (TMP) and d₅-pyridine(deuterated pyridine) as the basic probe molecules, the concentrations of Brönsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state ¹H and ³¹P magic-angle spinning (MAS) NMR. After adsorption of the probe molecules, the concentration of Brönsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas that in the parent HY sample remains almost unchanged. The increase in the concentration of Brönsted acid sites is due to the appearance of base-induced Brönsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is “induced” to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Brönsted acid sites has also been discussed.     

The design of photocatalysts for the removal of NOx at normal temperatures—Copper (I) and silver (I) ion catalysts anchored within zeolite cavities

The Cu⁺/ZSM-5 and Ag⁺/ZSM-5 catalysts were prepared by a combination of ion-exchange and thermovacuum treatments. In situ photoluminescence, ESR, XAFS, UV-VIS and FT-IR measurements of the catalysts revealed that within the cavity of the ZSM-5 zeolite, the Cu⁺ ion or Ag⁺ ion exists in an isolated state. UV irradiation of the catalysts in the presence of NO at normal temperature led to the formation of N₂ and O₂ for Cu⁺/ZSM-5 and N₂, N₂O and NO₂ for Ag⁺/ZSM-5, indicating that the isolated Cu⁺ ion or Ag⁺ ion acts as a photocatalyst for the direct decomposition of NO. However, the Cu⁺/ZSM-5 catalyst loses its photocatalytic reactivity under the coexistence of O₂, while the Ag⁺/ZSM-5 catalyst maintains its reactivity under the coexistence of O₂ and H₂O.     

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu‐SSZ‐13

Operando X‐ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu‐exchanged SSZ‐13. Catalysts prepared to contain only isolated, exchanged Cu^II ions evidence both Cu^II and Cu^I ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH₃ together are necessary for Cu^II reduction to Cu^I. DFT calculations show that NO‐assisted NH₃ dissociation is both energetically favorable and accounts for the observed Cu^II reduction. The calculations predict in situ generation of Brønsted sites proximal to Cu^I upon reduction, which we quantify in separate titration experiments. Both NO and O₂ are necessary for oxidation of Cu^I to Cu^II, which DFT suggests to occur by a NO₂ intermediate. Reaction of Cu‐bound NO₂ with proximal NH₄⁺ completes the catalytic cycle. N₂ is produced in both reduction and oxidation half‐cycles.     

ESR and TPD Study of the Interaction of Nitromethane and Ammonia with HZSM-5 and CuZSM-5 Zeolites

The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the course of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures T _dec. One is due to the formation of the Cu²⁺(NH₃)₄ complex (T _dec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu²⁺O^– and Cu²⁺–O^2––Cu²⁺, or CuO clusters (T _dec = 650–750 K). Ammonia adsorption on Cu⁺ and Cu⁰ is negligible compared with that on the Brönsted acid sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400–500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Brönsted acid sites and copper(II) similar to those formed in the course of adsorption from the gas phase, but the Cu²⁺(NH₃)₄ complexes on CuZSM-5 are not observed. Possible structures of ammonia and nitromethane complexes on Brönsted acid sites and the Cu²⁺ cations in zeolite channels are discussed. The role of these complexes in selective NO _x reduction by hydrocarbons over the zeolites is considered in connection with their thermal stability.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

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.     

Effect of the nature of support and Cu precursor on the activity of copper-containing catalysts in CO oxidation

We have studied the catalytic activity of supported copper-containing catalysts based on ZSM-5, Al₂O₃, and SiO₂ in oxidation of CO. We have established that the difference between the activities of systems with 1.8% copper content obtained from different precursors is determined by the different reducibilities of their active sites, the number of such sites, and the distribution of the metal ions. The fact that the activity is highest for 1.8% Cu-ZSM-5 obtained from copper acetate is due to the relatively higher number of associated Cu²⁺ cations in square planar coordination in a non-lattice oxygen environment, which have high reducibility, and the higher overall oxygen content O_ads + O_OH in the surface layer of the catalyst.     

Ethylene and propylene adsorption and the formation of hydrocarbon complexes with NO2 upon interaction of adsorbed olefins with an NO + O2 mixture over HZSM-5 and CuZSM-5 zeolites studied by TPD and ESR

Adsorption of C₂H₄ and C₃H₆ on copper in oxidized samples of CuZSM-5 is found to increase with the copper concentration; simultaneously, olefin adsorption on the Br?nsted acid sites decreases. The Cu²⁺ cations in the square-planar coordination exhibit higher reactivity in olefin adsorption than copper cations in the square-pyramidal coordination. Thermal treatment of CuZSM-5 with hydrogen results in regeneration of the Br?nsted acid sites for olefin adsorption and the disappearance of Cu²⁺ cations, the active sites of adsorption, due to the reduction of Cu²⁺ to Cu⁺ and Cu⁰. Desorption peaks appear in the TPD spectra upon the interaction between the adsorbed hydrocarbons and NO₂. These peaks are not observed upon separate adsorption of the reactants, and they are likely due to decomposition of NO₂-hydrocarbon complexes over both the Br?nsted and copper-containing sites of the zeolite     

Molecular and dissociative adsorption of H2O on zeolite Zn/ZSM-5 studied by diffuse-reflectance IR spectroscopy and quantum chemical calculations

Interest in water adsorption on cation-substituted zeolites is due to the possibility of the M ⁿ⁺ (H₂O) + [Si-O-Al]^?1 → MOH^{(n ? 1)+} + Si-O(H)-Al (M = metal, n = 1–3) reaction taking place. As a result of this reaction, the cation-substituted zeolite can exhibit Brønsted acid activity. The molecular adsorption of water on Zn/ZSM-5 zeolite at room temperature and the subsequent heterolytic dissociation of adsorbed water under heating have been investigated by diffuse-reflectance IR spectroscopy. For theoretical simulation of these processes, three different fragments of the ZSM-5 lattice corresponding to possible variants of the structure of the ionic site of the substituting cation have been examined. Calculations on the molecular and dissociative adsorption of water molecules on substituting Zn²⁺ cations have been performed by the DFT method. Two pathways of the dissociation of adsorbed H₂O molecules-endothermic and exothermic ones-have been discovered, and it has been demonstrated that the spatial separation of two lattice Al ions at the Zn²⁺ cation site significantly affects the adsorption energy.     

Host-guest chemistry of copper(II)-histidine complexes encaged in zeolite Y

Structural analysis has been carried out on copper(II )–histidine (Cu²⁺/His) complexes after immobilization in the pore system of the zeolites NaY and de‐aluminated NaY (DAY). The aim of this study was to determine the geometrical structure of Cu²⁺/His complexes after encaging, to obtain insight into both the effect of the zeolite matrix on the molecular structure and redox properties of the immobilized complexes. In addition to N₂ physisorption and X‐ray fluorescence (XRF) analyses, a combination of UV/Vis/NIR, ESR, X‐ray absorption (EXAFS and XANES), IR, and Raman spectroscopy was used to obtain complementary information on both the first coordination shell of the copper ion and the orientation of the coordinating His ligands. It was demonstrated that two complexes ( A and B ) are formed, of which the absolute and relative abundance depends on the Cu²⁺/His concentration in the ion‐exchange solution and on the Si/Al ratio of the zeolite material. In complex A , one His ligand coordinates in a tridentate facial‐like manner through N_am, N_im, and O_c, a fourth position being occupied by an oxygen atom from a zeolite Brønsted site. In complex B , two His ligands coordinate as bidentate ligands; one histamine‐like (N_am, N_im) and the other one glycine‐like (N_am, O_c). In particular the geometrical structure of complex A differs from the preferred structure of Cu²⁺/His complexes in aqueous solutions; this fact implies that the zeolite host material actively participates in the coordination and orientation of the guest molecules. The tendency for complex A to undergo reduction in inert atmosphere to Cu¹⁺ (as revealed by dynamic XANES studies) suggests activation of complex A by the interaction with the zeolite material. EXAFS analysis confirms the formation of a distorted four coordinate geometry of complex A , suggesting that the combination of zeolite and one His ligand force the Cu²⁺ complex into an activated, entactic state.     

Untersuchungen an oxidischen Katalysatoren. XLII. Redoxverhalten des Nickels in NiNa?Y-Zeolithen 4. Einfluß der Zusammensetzung auf die Reduzierbarkeit von Nickel in NiNa?Y-Zeolithen

Studies on Oxide Catalysts. XLii. Redox Behaviour of Nickel in Zeolites NiNa? Y. 4. Influence of Composition on the Reducibility of Nickel in Zeolites NiNa? Y By chemical analysis (reaction with K₂Cr₂O₇) and ESCA investigations we determined the degree of reduction in reduced samples NiNa-Y as function of the mole ratio SiO₂/Al₂O₃ (module), of the Ni²⁺ degree of exchange and the kind of the second cations. (NH₄₊, Ca²+, Co²+, and Nd³+) in the temperature region of 620–770 K. The degree of nickel reduction increases with increasing module, decreasing degree of exchange and decreasing number of Brönsted acidic centres. This behaviour is caused by the influence of the interaction between cations Ni²⁺ and zeolite lattice on the reduction equilibrium.     

Configuration of MFI-type zeolite interacting with the probe molecule P(CH<Subscript>3</Subscript>)<Subscript>3</Subscript> – a theoretical study

With P(CH₃)₃ as the probe molecule adsorbed on titanium silicalite (TS-1) zeolite, the special and important role of T12 site in MFI-type zeolite was clearly elucidated. There are altogether three active sites present in TS-1 zeolite with Ti at the T12 site. Owing to the preferential adsorption of probe molecules on the first Brönsted acidic site, the Ti12 center will probably fail to show Lewis acidity. The ionic [HP(CH₃)₃]⁺ species can be stabilized by the first or second Brönsted acidic site, with the former energetically favored. The latter was formed through the transfer of the ionic [HP(CH₃)₃]⁺ species from the first to the second Brönsted acidic site.