丙烯醇催化氨化合成3-甲基吡啶催化剂的制备及性能

采用浸渍法制备了一系列H-ZSM-5分子筛负载过渡金属锌催化剂,在固定床反应器上考察了这些催化剂对丙烯醇催化氨化合成3-甲基吡啶的催化性能。通过对H-ZSM-5的硅铝比、锌负载量对催化剂催化性能影响的考察,发现硅铝比为80、锌负载量为12%时得到的催化剂Zn₁₂/H-ZSM-5（80）的催化性能最佳。在常压、反应温度420℃、氨醇摩尔比3：1、空速300 h^-1条件下,丙烯醇在该催化剂上的转化率和3-甲基吡啶的选择性分别达到97.8%和37.9%。利用X射线衍射（XRD）、X射线光电子能谱（XPS）以及吡啶吸附红外对催化剂进行了表征,结果表明,Zn₁₂/H-ZSM-5（80）上负载的Zn²⁺为L酸;在丙烯醇生成3-甲基吡啶的反应过程中催化剂的脱氢活性物种为氧化锌,而加成和环合反应则主要是由催化剂中的L酸催化实现的。     

A Novel Radioisotope Method for Studying Catalytic Transformations over Alumina, H-ZSM-5 and H-Beta Zeolite Catalysts: Investigation of Conversion of 11C-Labeled Methanol to 11C-Labeled Dimethyl Ether and Hydrocarbons

A novel radiochemical method for investigating the catalytic transformations of the ¹¹C-radioisotope labeled methanol over H-ZSM-5 and H-Beta zeolite catalysts has been introduced. The catalysis process was monitored by gamma detectors and the ¹¹C-labeled products were analyzed by radio-gas chromatography. The medium pore H-ZSM-5 and H-Beta zeolite catalysts were synthesized and characterized using X-ray powder diffraction, scanning electron microscope, nitrogen adsorption, X-ray fluorescency and FTIR spectroscopy. The investigations of ¹¹C-labeled product distributions and reaction mechanism of the conversion of [¹¹C]methanol over H-ZSM-5 and H-Beta zeolite catalysts have been elaborated in terms of structure and acidity of the catalysts. In microreactors the effect of natural carbon compounds from environment can be a disturbing effect for the detection of inactive carbon products. Applied radio detection method eliminates these disturbing effects and detects only ¹¹C-labeled compounds during the whole catalytic process. In the study of the transformations of carbon compounds, besides the well known ¹⁴C tracer technique and ¹³C MAS NMR spectroscopy investigation, the ¹¹C-method is a new, more sensitive and simple one to monitor the transformation of the starting ¹¹C-labeled compound by radio detectors (gamma detector) and for analyzing the ¹¹C-labeled products by radio-gas chromatography.     

Unit cell thick nanosheets of zeolite H-ZSM-5: Structure and activity

Nanosheets of zeolite H-ZSM-5 were synthesized and characterized by X-ray diffraction, transmission electron microscopy (TEM), N₂-physisorption, FT-IR spectroscopy, ²⁷Al and ²⁹Si MAS NMR spectroscopy in addition to catalytic testing in conversion of methanol to hydrocarbons (MTH). It was found that Rietveld analysis, involving anisotropic broadening parameters, gave average crystallite dimensions in good agreement with TEM images. The selectivities in MTH is intact in the mesoporous nanosheet H-ZSM-5 with the largest difference being a higher C₃/C₂ ratio compared to regular H-ZSM-5.     

富氧条件Co/H-ZSM-5催化剂上CH4选择催化还原NO的研究

采用离子交换法制备了一系列具有不同硅铝比和不同Co负载量的Co/H-ZSM-5催化剂样品。富氧条件下考察了硅铝比、Co负载量、空速、O₂浓度及酸位对催化剂选择催化还原活性的影响。并对其进行了XRD、BET、H₂-TPR和DRS-UV-vis等表征。催化结果表明，催化剂的催化活性随Co负载量的增加而增加，随硅铝比的增加而减少；NO转化率随着空速的增加而降低。O₂体积分数为2%时，NO达最大转化率。表征结果表明，Co²⁺为活性中心，酸中心的存在对催化活性有一定的促进作用。     

Molybdenum substitution by copper or zinc in H-ZSM-5 zeolite for catalyzing the direct conversion of natural gas to petrochemicals under non-oxidative conditions

This work aims to investigate the influence of substituting half the Mo content in a standard 6%Mo/H-ZSM-5 catalyst with either Cu or Zn in H-ZSM-5 support, on the direct conversion of methane in a flow-type fixed-bed reactor atmospherically at 700 °C at a gas hourly space velocity 1500 cm³ h⁻¹ g⁻¹ and times-on stream (TOS) up to 240 min. The most active was 6%Mo/H-ZSM-5 catalyst while Mo-Zn/H-ZSM-5 was more active than Mo-Cu/H-ZSM-5. The XRD data showed that the crystallite (particle) sizes were found compatible with the catalytic activities. At the initial TOS (5 min), methane splitting selectivity to C and H₂ approached 100%. Higher carbon deposition on Mo-Cu catalyst caused more inhibition of ethylene further conversion to larger hydrocarbons thus leading to ethylene accumulation. TPR showed an almost complete reduction of Cu oxides at relatively lower temperatures such that the Mo-Cu catalyst acquired the highest dehydrogenation activity that enhanced markedly ethylene formation. An outstanding accomplishment is obtaining the highest benzene yield and selectivity using Mo-Zn/H-ZSM-5 catalyst, which is a prosperous challenge against the standard monometallic one. The large size of naphthalene molecule caused significant diffusion restriction on its formation in catalytic pores. The exceptional enhancement of naphthalene yield and selectivity at longer TOS using the Mo-Cu/H-ZSM-5 catalyst can be indicative that naphthalene was mostly formed on external zeolitic surface.     

Preparation of In,H-ZSM-5 for DeNOx reactions by solid-state ion exchange

A simple method is proposed to prepare In,H-ZSM-5 catalyst for DeNOx reactions. This consists of mechanically mixing the fine powders of In₂O₃ and H-ZSM-5 followed by heating in oxygen free inert gas flow to 580 °C where indium undergoes thermal auto-reduction and moves into exchange positions as In⁺ without destroying the crystalline structure of the zeolite.It was evidenced by IR, temperature-programmed reduction (TPR) and reoxidation that, once In⁺ was introduced into the lattice either by reductive solid-state ion exchange (RSSIE) or by thermal auto-reductive SSIE, it can be oxidized by O₂ or in the DeNOx reaction to (InO)⁺. The formed (InO)⁺ can easily be reduced to In⁺ suggesting that In,H-ZSM-5 might be a good catalyst for reactions where a redox cycle in the catalyst is involved in the reaction mechanism.Selective catalytic reduction (SCR) by methane proved that only a small fraction of In exchanged, together with some acid sites of the zeolite formed the active center for the catalytic reaction. XRD, XPS and FT-IR using pyridine proved that the structure of the zeolite and these centers are stable under reaction conditions and In is mainly in the form of (InO)⁺ in the used catalyst.     

Effects of cobalt precursor on pyrolyzed carbon-supported cobalt-polypyrrole as electrocatalyst toward oxygen reduction reaction

A series of non-precious metal electrocatalysts, namely pyrolyzed carbon-supported cobalt-polypyrrole, Co-PPy-TsOH/C, are synthesized with various cobalt precursors, including cobalt acetate, cobalt nitrate, cobalt oxalate, and cobalt chloride. The catalytic performance towards oxygen reduction reaction (ORR) is comparatively investigated with electrochemical techniques of cyclic voltammogram, rotating disk electrode and rotating ring-disk electrode. The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure. It shows that the cobalt precursor plays an essential role on the synthesis process as well as microstructure and performance of the Co-PPy-TsOH/C catalysts towards ORR. Among the studied Co-PPy-TsOH/C catalysts, that prepared with cobalt acetate exhibits the best ORR performance. The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR. Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too.     

Liquid-phase dehydrocondensation of 1-pentanol to di-n-pentyl ether (DNPE) over medium and large pore acidic zeolites

The present paper deals with the liquid-phase synthesis of di-n-pentyl ether (DNPE) by dehydration of 1-pentanol over H-Beta, H-ZSM-5, H-mordenite and H-Y zeolites. Their SiO₂/Al₂O₃ ratios were about 25 for H-Beta, 28 for H-ZSM-5, 35 for H-mordenite and 6 for H-Y. Experiments were performed in a batch reactor in the temperature range 140–180 °C at 1.6 MPa. Comparison of the catalysts behaviour shows that H-Beta is the most active and selective to DNPE, although it is less active than microporous ion-exchange resins. Kinetics of DNPE synthesis was studied. The best kinetic model for all the catalysts stems from a reaction mechanism whose rate-limiting step is the surface reaction between two 1-pentanol molecules adsorbed on adjacent sites, to yield DNPE and water both adsorbed on single site. Activation energy, on each single catalyst, was estimated to be in the range 94–118 kJ mol^?1.     

Completed encapsulation of cobalt particles in mesoporous H-ZSM-5 zeolite catalyst for direct synthesis of middle isoparaffin from syngas

The completed encapsulation cobalt clusters inside the channels of mesoporous H-ZSM-5 zeolite catalyst was synthesized using mesoporous carbon as a hard template and evaluated in Fischer–Tropsch synthesis (FTS) for direct synthesis of middle isoparaffin. The characterization and catalytic performance tests revealed that the acid sites of mesoporous zeolite tuned FTS product distribution. The isoparaffin selectivity of Co/MZ was 34.6% to become the main FTS products because of the optimized hydrocracking and isomerization function of the mesoporous structure of H-ZSM-5 support. The novel route of catalyst preparation, first reported here, can also be extended into other clean fuel synthesis fields.     

Identification and Influence of Acidity on Alkylation of Phenol with Propylene over ZSM-5

The alkylation of phenol with propylene has been studied over several H-ZSM-5s with different Si/Al ratios and Cs⁺-ion-exchanged H-ZSM-5s at temperature range 373–623°C. Both O- and C-alkylation, which were closely dependent on the reaction temperature and acidity of the catalysts, were observed. O-alkylated compound is found to be formed preferably at temperature lower than 250°C and over Cs⁺-ion-exchanged H-ZSM-5s. However, at higher temperature, only C-alkylation is observed. The acidic properties of the zeolites were characterized by solid-state ³¹P MAS-NMR of the probe molecule trimethylphosphine oxide and NH₃-TPD (temperature-programmed desorption) and it is suggested that in the case of C-alkylation, moderate acid sites are responsible for the formation of para-isopropylphenol, while ortho-isopropylphenol is favorable for weak acid sites.     

Selective Catalytic Reduction of NO with NH3 over Fe-ZSM-5 Catalysts Prepared by Sublimation of FeCl3 at Different Temperatures

Fe-ZSM-5 catalysts were prepared by subliming FeCl₃ into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl₃ exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl₃ into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl₃ at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl₃ at 700 °C were found to be more active for NO reduction with NH₃ in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl₃ at 320 °C. To determine the active sites, the catalysts were characterized by H₂-TPR, in situ DRIFTS of NO adsorption, NH₃-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH₃ could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when positions in Fe-ZSM-5, corresponding to Fe²⁺(NO) band at 1877 cm^-1 in DRIFTS, were preferentially occupied.     

Spectroscopic investigations on deactivation of zeolite catalysts during reactions of olefins

Coke formation over acidic zeolite catalysts upon reaction of olefins is investigated using in-situ IR spectroscopy, i.e. an IR cell which simultaneously serves as a fixed-bed flow reactor and is attached to a gas chromatograph. Zeolites HY, dealuminated H-MOR with two different Si/Al ratios and H-ZSM-5 are compared. The effects of the number of active sites and the pore volume of the zeolites on the initial rate of coke formation and the final coke level are studied.

The final level of coke deposition reflects to some extent the pore volume of the zeolite catalyst. In all cases a considerable amount of coke formed remained inside the pore structure but another fraction was deposited onto the external surface. Both findings were confirmed by sorption measurements on samples before and after loading with coke.

Possible mechanisms of deactivation through coke formation, viz, poisoning, consumption or blockage of sides are briefly considered. In-situ IR spectroscopy revealed that at most a small fraction of the active sites of HY, HMOR or HZSM-5 disappeared during coke deposition suggesting that deactivation is caused by site blocking rather than by poisoning or consumption of the acidic centres.

Finally, in-situ IR spectroscopy turned out to be a useful tool for discriminating between low-temperature coke (formed below about 500 K) and high-temperature coke (deposited above 500 K).     

In situ MAS NMR investigations of molecular sieves and zeolite-catalyzed reactions

Solid-state MAS NMR is a powerful technique to study heterogeneous catalysts and the way by which they operate. In situ MAS NMR has been demonstrated to be a powerful method to understand reaction mechanisms, to study the nature, dynamics and reactivity of surface intermediates and active sites, and to characterize structural modifications in the catalyst itself, in particular when using ¹³C strategically labelled substrates. In this paper, three examples selected from our own work are used to illustrate the potential of in situ MAS NMR. They are the formation of cumene and its isomerization to n-propylbenzene on zeolite H-ZSM-11, the activation of propane at low temperature and the alkylation of benzene with propane on zeolite H-ZSM-5, and the characterization of the aluminophosphate molecular sieve VPI-5 structure with temperature. Studies of the alkylation of benzene with propene confirmed that cumene was the primary reaction product. The undesired n-propylbenzene by-product results from the intermolecular reaction between cumene and benzene, enhanced by molecular shape-selective effects in medium pore size zeolites (e.g., H-ZSM-11). It explains why large pore zeolites, e.g., zeolite Beta, are used commercially today for this process. Propane can be activated at low temperature (ca. 573 K) on bifunctional medium pore size zeolites possessing intimately related acidic Brønsted sites and a dehydrogenation function provided by Ga or Zn species. In Ga/H-ZSM-5 catalysts, at 573 K, the activation of propane was shown to occur via a protonated pseudocyclopropane (PPCP) intermediate (or transition state). The latter evolves in a manner that can be formally described by the formation of CH ₃ ⁺ , C₂H ₂ ⁺ , and C₃H ₇ ⁺ carbenium ion intermediates. These species can react with olefins, alkanes, or other electron-rich molecules such as benzene. The primary reaction products of the reaction of propane with benzene are n-propylbenzene (in small amount), ethylbenzene and toluene. Their subsequent reactions lead eventually to toluene and xylenes as the final products. In the structural characterization of VPI-5, ²⁷Al, ³¹P, and ²⁷Al nutation MAS NMR spectra show that, at 294 K, fully hydrated VPI-5 contains three equally populated Al and P crystallographic sites and that one-third of Al is 6-coordinate. The VPI-5 structure then belongs to the P6₃ space group. Above 353 K, VPI-5, fully or partially hydrated, undergoes a structural transformation to a higher framework symmetry, i.e., the P6₃cm space group. The transformation occurs at nearly the same temperature in both cases, indicating that the breakdown of the hydrogen-bonded helical water structure inside the VPI-5 pores is not a factor in the process.     

Methanol to propylene: the effect of iridium and iron incorporation on the HZSM-5 catalyst

The effect of iridium and iron impregnation of HZSM-5 zeolite on the methanol to propylene reaction (MTP) was investigated. The selectivities of propylene and other hydrocarbons, and the conversion of methanol were compared by performing MTP in a small pilot plant. The results indicate that HZSM-5 zeolite modified by iron and iridium increased propylene selectivity by 6.3% and 8%, respectively. The selectivity of propylene was higher for Ir/H-ZSM-5 than for Fe/H-ZSM-5, where Fe/H-ZSM-5 was more stable than Ir/H-ZSM-5. Analytic techniques, including X-ray diffraction, BET surface area, temperature-programmed desorption of ammonia, and inductively coupled plasma atomic emission spectroscopy, were used to characterize the modified zeolites as well as the parent zeolites.     

Method for distinguishing Brønsted-acid sites in mixtures of H-ZSM-5, H-Y and silica-alumina

We have examined the adsorption and reaction of ethylamine, isopropylamine, 2-ethylhexylamine, cyclooctylamine, and diphenylethylamine on H-ZSM-5, H-Y, and silica-alumina samples using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA). Each of the amines decomposes at Brønsted-acid sites to alkene and ammonia products above 550 K by a reaction similar to the Hofmann elimination reaction, so that the number of molecules which decompose can be used to measure the number of acid sites in the sample. For H-ZSM-5, the concentration of sites determined using ethylamine and isopropylamine was approximately equal to the framework aluminum concentration; however, adsorption of cyclooctylamine and 2-ethylhexylamine in H-ZSM-5 was limited so that only a fraction of the sites were counted using these probe molecules. For the silica-alumina and H-Y samples, the concentrations of Brønsted-acid sites could be determined using ethylamine, isopropylamine, 2-ethylhexylamine, or cyclooctylamine; and the site concentrations determined in this way were essentially dependent of which amine was used. 2,2-Diphenylethylamine adsorption was limited on both silica-alumina and H-Y samples, but a much higher fraction of the Brønsted-acid sites on the silicaalumina sample could be counted. These results indicate that TPD-TGA measurements with various amines can be used to determine the concentration of Brønsted-acid sites in each of the components of a fluid-catalytic-cracking catalyst.     

Dinitrogen as a probe of acid sites of zeolites

Nitrogen adsorption on H-ZSM-5 and H-Y zeolites at low temperatures were studied by in situ FT-IR spectroscopy. For each zeolite, two absorption bands were observed at around 2334 and 2352 cm^–1 in thev(NN) region and were assigned to thev(NN) mode of dinitrogen species adsorbed on Brønsted and Lewis acid sites of the zeolites, respectively. These results and previous results for H-mordenite suggest that dinitrogen serves as a probe of acid sites and its advantages as probe are discussed.     

Selective Catalytic Reduction of NOx over H-ZSM-5 Under Lean Conditions Using Transient NH3 Supply

The selective catalytic reduction (SCR) of NO _x over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NO _x , O₂ and either pre-adsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO₂. With transient ammonia supply the total NO reduction increased and the selectivity to N₂O formation decreased compared to continuous supply. The FTIR experiments revealed that NO _x reacts with ammonia adsorbed on Brønsted acid sites as NH₄ ⁺ ions. These experiments further indicated that adsorbed -NO₂ ^– is formed during the SCR reaction over H-ZSM-5.     

A continuous process for the production of 2,2,6,6-tetramethylpiperidin-4-ol catalyzed by Cu-Cr/γ-Al2O3

A continuous process was established for the production of 2,2,6,6-tetramethylpiperidin-4-ol over Cu-Cr/γ-Al₂O₃ in a fixed-bed reactor. The catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction. Cu⁰ was believed to be the active site for the hydrogenation, and the doped chromium was supposed to exert a positive impact on the dispersion of active species. The catalyst and parameters of hydrogenation were optimized. Thus, 2,2,6,6-tetramethylpiperidin-4-ol was obtained in the yield of 90% from 2,2,6,6-tetramethylpiperidin-4-one (purity, 95%) under the optimum reaction conditions.     

Direct observation of carbon nanotube formation in Pd/H-ZSM-5 and MoO3/H-ZSM-5 based methane activation catalysts

The nature of carbonaceous species deposited upon MoO₃/H-ZSM-5 and Pd/H-ZSM-5 based catalysts during methane activation at 700 °C has been studied. TEM evidences the formation of open-ended multi-walled carbon nanotubes on MoO₃/H-ZSM-5 based dehydroaromatisation catalysts. Pd/H-ZSM-5 is more active, exclusively towards methane cracking and post-reaction analysis reveals the distribution of different carbonaceous species is more homogeneous which TEM demonstrates to be in the form of closed-end multi-walled carbon nanotubes.     

Methanol Conversion to Hydrocarbons (MTH) Over H-ITQ-13 (ITH) Zeolite

Product flexibility is key to meeting fluctuating chemicals demands in the future. In this contribution, the methanol to hydrocarbons (MTH) reaction was investigated over two Ge-containing H-ITQ-13 samples, one with needle-like (H-ITQ-13(N), with (Si+Ge)/Al) = 42) and another with plate-like (H-ITQ-13(P), with (Si+Ge)/Al > 100) morphology. The samples were characterised using XRD, BET, SEM/EDS and FTIR spectroscopy, and their MTH performance was compared with the performance of H-ZSM-5 and H-ZSM-22. Similar specific surface areas (413 and 455 m² g^?1 for H-ITQ-13(N) and (P), respectively) and similar acid strength (Δν ~ ?327(?310) cm^?1) was observed for the two H-ITQ-13 samples. Testing of H-ITQ-13(N) at weight hourly space velocity (WHSV) = 2–8 h^?1 at 350–450 °C revealed that C₅₊ alkenes were the main products (35–45 % selectivity at 400 °C), followed by propene and butene. A low but significant selectivity for aromatic products was observed (6–8 % selectivity at 400 °C). Product selectivity was found to be independent of deactivation. The methanol conversion capacity of H-ITQ-13(N) was 120–150 g methanol g^?1 catalyst at 400 °C. Testing H-ITQ-13 at high (30 atm) and ambient pressure, respectively, at 350 °C showed that a high pressure led to enhanced C₅₊ selectivity, but close to a tenfold decrease in methanol conversion capacity. H-ITQ-13(P) was tested at 400 °C and 2 h^?1. It gave lower conversion than H-ITQ-13(N). Furthermore, when compared at the same conversion level, H-ITQ-13(P) gave higher C₅₊ alkene selectivity, lower aromatics selectivity, and a higher propene to ethene ratio than H-ITQ-13(N). The H-ITQ-13 samples yielded a product spectrum intermediate of H-ZSM-22 and H-ZSM-5. The effluent product cut-off of H-ITQ-13 was similar to that of H-ZSM-5 with tetramethylbenzene as the largest significant product, while H-ZSM-22 produced mainly linear and branched alkenes. The lifetime of H-ITQ-13(N) was clearly enhanced compared to H-ZSM-22, but inferior to H-ZSM-5.