The effect of phase transition of methanol on the reaction rate in the alkylation of hydroquinone

An O-alkylation reaction of hydroquinone with excess methanol was carried out by using alkaline metal ion-exchanged zeolite catalysts at various phases of methanol in a slurry type reactor. The amount of methanol, used as a methylating agent and also a solvent, significantly affected the reaction rate. When the amount of methanol was decreased from 2 mol to 0.6 mol, the reaction rate was increased more than nine times. These changes in the reaction rate could be explained by the pressure change and the phase transition of the reactant, methanol, depending on the temperature and the elimination of a diffusion limitation of reactants through the zeolite pores in a gas phase condition. Thus, higher than 89% selectivity to 4-methoxyphenol was obtained at 80% conversion of hydroquinone at a gas phase reaction condition using 1 mol of methanol for 2 hours.     

Effects of adsorbed oxygen containing molecules on the XANES of Pt in supported Pt/SiO2 catalysts

Selective reduction of nitric oxide with propane in the presence of excess oxygen was investigated using gallium ion-exchanged zeolite catalysts. Gallium ion-exchanged ferrierite (Ga-ferrierite) showed extremely high selectivity for this reaction under oxygen-rich conditions (10%). The molar ratio of reacted NO to consumed C₃H₈ was found to be near 3 on Ga-ferrierite.     

Selective oxidation of methanol in exhaust gas containing aromatic compounds

The activity of exhaust catalysts of methanol and gasoline mixture fueled automobiles is inhibited by coexistent aromatic compounds contained in the exhaust stream. One approach to avoid this inhibition could be the utilization of a molecular-sieve effect. It seems probable that the migration of aromatic compounds, which have larger molecular sizes than that of methanol, will be blocked by these supports and methanol will selectively reach the active sites of the catalysts. Thus, we examined the simultaneous oxidation of methanol and toluene over some ion-exchanged Pt/zeolite catalysts. Experimental results showed that ion-exchanged Pt/zeolite catalysts are less affected by coexistent toluene and have a higher selectivity for methanol oxidation compared with an alumina-supported platinum catalyst, suggesting that the use of these catalysts is effective for oxidizing methanol in the exhaust stream containing aromatic compounds. Among the catalysts tested, a Pt/H-MOR catalyst was found to be the most effective for the oxidation of methanol and effectively catalyzed the reaction in the presence of toluene even at low temperature.     

甲苯侧链烷基化催化剂的评选及反应性能研究

用脉冲微反技术对甲醇-甲苯侧链烷基化反应催化剂进行了评价,发现在所用几种催化剂中,X型沸石的活性和选择性最佳。随着交换的碱金属离子半径的增大,活性和选择性均有增大趋势。用H3BO3 和CaO对KX沸石进行改性后可显著提高侧链烷基化选择性。将浸渍H3BO3的KX和碱土化合物改性的KZSM-混合而成的双组分催化剂具有良好的活性和选择性。     

Highly selective Pd/KX catalysts for low-pressure one-step synthesis of 2-ethylhexanal from n-butyraldehyde and hydrogen

2-ethylhexanal (2EH) was directly synthesized from n-butyraldehyde and hydrogen at 1 atm and 150°C using the catalysts prepared by supporting tetraamine palladium(II) chloride on the potassium ion-exchanged zeolite X (Pd/KXW) and on the potassium ion-added zeolite X (Pd/KXU). The latter catalyst contains a larger amount of potassium ion and exhibits higher activity and very high selectivity of 2EH (>93%) due to its greater basicity. The main reaction path possibly starts from self-condensation of n-butyraldehyde on the catalyst basic sites to form 2-ethyl-3-hydroxyhexanal followed by dehydration to 2-ethyl-2-hexenal which was then hydrogenated on the metallic Pd sites to 2EH. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hβ沸石修饰的复合氧化物对苯酚羟基化反应的催化作用

采用不同硅铝比的Hβ沸石对铁基复合金属氧化物催化剂进行了修饰,发现复合氧化物催化体系中掺入适量具有特定结构的Hβ沸石,可以提高催化剂的活性,缩短甚至消除羟基化反应诱导期,避免由于未反应过氧化氢的积累增加反应器运行的风险,提高过氧化氢有效利用率和目标产物选择性。但过多的Hβ沸石导致苯酚和苯二酚缩合生成不溶于水的焦油,降低了羟基化反应的目标产物选择性。比较合适的修饰用Hβ沸石包括Hβ-80、Hβ-63和Hβ-48。比较好的Hβ-80沸石掺入质量分数为7%,以7% Hβ沸石修饰的Fe-Cu-Sn-Zn-O/γ-Al2O3复合氧化物作催化剂,反应温度65 ℃、反应时间30 min、苯酚5.3 g、溶剂水10.0 g、m(苯酚)∶m(催化剂)=294、n(过氧化氢)∶n(苯酚)=0.33时,反应诱导期不到1 min,苯酚转化率22.3%,苯二酚选择性91.9%,过氧化氢有效利用率62.1%。     

Hydroxylation of phenol with H2O2 over transition metal containing nano-sized hollow core mesoporous shell carbon catalyst

The catalytic performance of transition metal (Fe²⁺ or Cu²⁺) containing nano-sized hol low core mesoporous shell carbon (HCMSC) heterogeneous catalysts for the hydroxylation of phenol with hydrogen peroxide (H₂O₂) in water was investigated in a batch reactor. The metal-containing HCMSC catalyst showed higher activity than the same metal ion-exchanged zeolites. The nature of the metal and its content in the HCMSC had remarkable influence on the reaction results under the typical reaction conditions (PhOH/H₂O₂=3, reaction temperature=60 ‡C). Fe²⁺ containing HCMSC catalyst showed high catalytic activity with phenol conversion of 29%, selectivity to catechol (CAT) and hydroquinone (HQ) about 85%, H₂O₂ effective conversion about 70% and selectivity to benzoquinone (BQ) below 1% in the batch system.     

Alkylation of Hydroquinone with tert-Butanol Catalyzed by Polymer-supported Sulfonimide

Polystyrene with pendant perfluorobutylsulfonylimide (PPFSI) was developed as a novel polymer-supported strong acid catalyst for alkylation of hydroquinone (HQ) with tert-butanol (TBA), and highly selective synthesis of 2-tert-butyl hydroquinone (2-TBHQ) was investigated over PPFSI under various experiment conditions. When the molar ratio of TBA to HQ was 1.2:1, using 3 mol% of PPFSI as catalyst in 1,2-dichloroethane at 130 °C for 5 h, the maximum of selectivity (85.9%) of 2-TBHQ was obtained while the conversion of HQ was 76.7%. Compared with other solid acid catalysts PPFSI was found to be a very effective and reusable catalyst for alkylation of hydroquinone with tert-butanol.     

Ru/Na-H-ZSM-5双功能催化剂催化对苯二酚加氢

采用浸渍沉淀法制备了Ru/Na-H-ZSM-5系双功能催化剂,利用XRD、SEM、TEM、FT-IR及电泳仪等对催化剂结构、晶形外貌、孔道特点及表面电性进行测试,并在釜式反应器中进行催化性能评价。结果表明,Ru/Na-H-ZSM-5双功能催化剂用量0.5 g,反应压力3.0 MPa,反应温度130℃,反应时间3.0 h和Ru负载质量分数3.0%的条件下,对苯二酚转化率可达98.9%,目标产物1,4-环己二醇选择性达到85.2%。催化剂Ru/Na-H-ZSM-5用于对苯二酚加氢制备1,4-环己二醇反应活性组分Ru是关键所在,而分子筛结构以及电负性对于其反应有重要影响。     

4-甲氧基环己酮的绿色合成

在Al_2O_3负载的镍基纳米催化剂作用下进行了4-甲氧基苯酚催化加氢反应,然后使用双氧水对加氢反应液进行催化氧化合成4-甲氧基环己酮。在催化加氢反应中,考察了沉积-沉淀法和浸渍法及反应条件对催化剂活性和稳定性的影响。通过XRD、H_2-程序升温还原(H_2-TPR)及TEM等对催化剂进行了表征,结果发现,沉积-沉淀法制备的Ni/Al_2O_3-DP催化剂中活性粒子分散度高、粒径较小,并且活性粒子与载体之间有较强的作用力,具有比浸渍法制备的Ni/Al_2O_3-IMP催化剂更好的活性和稳定性。在4-甲氧基苯酚的加氢反应中,以Ni/Al_2O_3-DP为催化剂,最佳的反应条件为:反应温度423 K、反应压力4.0 MPa、反应时间1.0 h、m(4-甲氧基苯酚)∶m(Ni/Al_2O_3-DP)=6∶1。在氧化反应中,探究了氧化条件对反应活性的影响,结果表明:当n(4-甲氧基环己醇)∶n(双氧水)=1.0∶2.5时,353 K反应20 h,目标产物4-甲氧基环己酮的选择性可达95.3%。     

分子筛催化剂上二异丙苯异构化反应

通过筛选5种不同的催化剂，最终确定β沸石分子筛对二异丙苯异构化反应有良好的催化性能。考察了反应温度和空速对异构化反应转化率及选择性的影响，结果表明，170 ℃、3.5 MPa、空速2 h^－1下，β沸石上对二异丙苯的转化率45%，间二异丙苯的选择性69%。对催化剂的稳定性进行了考察，结果表明，在二异丙苯异构化反应中该催化剂表现出良好的稳定性。     

Oxidation of ketones over metal oxide catalysts: I. Catalytic synthesis of biacetyl from methyl ethyl ketone

The gas-phase oxidation of methyl ethyl ketone was studied on metal oxide catalysts in the presence of water vapor. Two types of competitive partial oxidations, i.e., biacetyl formation and oxidative scission reaction leading to acetaldehyde and acetic acid, took place on every oxide studied at 400–500 K. An approximate linear relationship was observed between the selectivity of each reaction and the acid-base property of the oxides; the former reaction was accelerated on the basic oxides such as Co₃O₄, while the latter reaction became predominant on the acidic oxides. As Co₃O₄ was the most effective biacetyl former of single-component oxides, modification of Co₃O₄ was examined to develop more effective catalysts for biacetyl synthesis. Scission reaction took the place of biacetyl formation over a catalyst where Co²⁺ ions were located in Y zeolite by an ion-exchanged method. Scission reaction was suppressed when Co oxide was supported on basic oxides such as MgO or CaO; however, the selectivity to biacetyl was slightly decreased due to the occurrence of a new reaction, acetone formation. The addition of Na₂O or Li₂O to Co₃O₄ was found to improve the selectivity to biacetyl without loss of catalytic activity. The maximum efficiency (13%) in biacetyl formation was attained at a Li content of ca. 7 at.%.     

Titanosilicate ETS-10 as a Lewis acid catalyst in the Meerwein–Ponndorf–Verley (MPV) reaction

The potential of ETS-10 as a Lewis acid catalyst was investigated using the MPV reaction at one atmosphere total pressure and 273 K. ETS-10 was hypothesized to be a potential Lewis acid catalyst as it has titanium in octahedral symmetry, which is the symmetry shown in zeolite Beta to be the most active site for the Lewis acid catalyzed Meerwein–Ponndorf–Verley (MPV) reaction. The MPV reaction is a hydrogen transfer reaction that can be used for obtaining information about the structure and performance of catalysts by comparing the product selectivities and catalytic activities. Due to their similar structures, the catalytic activity of ETS-10 was compared to zeolite Beta samples that were space-grown (flight, fewer defects) and to their earth-grown terrestrial controls. The higher tr-alcohol selectivity (i.e., trans-4-tert-butylcyclohexanol, ∼80% vs. 40%) observed over ETS-10 was attributed to a larger volume being available in the pores of ETS-10 compared to the zeolite Beta samples. By-product formation (i.e., 4-tert-butylcyclohexene) was significantly less over ETS-10 (∼5%) in comparison with the zeolite Beta samples (flight and control; ∼35%). These results reaffirm the octahedral symmetry as the Lewis active site for the MPV reaction, and illustrate that ETS-10 is a good catalyst for MPV type reactions.     

New Way of Hydroquinone and Catechol Synthesis using Nitrous Oxide as Oxidant

The synthesis of dihydroxybenzenes (DHB) via the gas‐phase oxidation of phenol with nitrous oxide in the presence of benzene was studied. Addition of benzene to the feed mixture greatly improves the selectivity and catalytic stability of the Fe‐containing ZSM‐5 zeolite, that was previously considered to be a main obstacle to the development of a new process. Reaction conditions strongly affect the distribution of the DHB isomers: the ratio of hydroquinone to catechol may vary from 1.4 to 10, with the resorcinol fraction being nearly constant and comprising 3–5%. Some 40 h experiments on the oxidation of a phenol‐benzene mixture demonstrated the high efficiency of the formed FeZSM‐5 catalyst. With a good stability, the catalyst provides 97% phenol selectivity referred to DHB and 85–90% N₂O selectivity referred to the sum of DHBs and phenol. A new process for hydroquinone and catechol synthesis based on the neat oxidation of benzene with recycling of the phenol as an intermediate product is suggested.     

K-L分子筛对甲苯芳环氯化选择性的影响

以K-L分子筛为催化剂,催化氯化甲苯制备邻/对氯甲苯,考察催化剂用量、粒径、重复使用次数、及溶剂等工艺条件对氯化选择性的影响。较优条件:氯化温度55℃,反应时间4h,催化剂粒径200目,K-L分子筛=10.0%,1,2-二氯乙烷=40.0%。在此条件下,甲苯转化率为99.8%,对氯甲苯选择性为84.1%,其催化性能优于工业常用的硫铁粉催化剂。     

Catalytic pyrolysis of waste rice husk over mesoporous materials

Catalytic fast pyrolysis of waste rice husk was carried out using pyrolysis-gas chromatography/mass spectrometry [Py-GC/MS]. Meso-MFI zeolite [Meso-MFI] was used as the catalyst. In addition, a 0.5-wt.% platinum [Pt] was ion-exchanged into Meso-MFI to examine the effect of Pt addition. Using a catalytic upgrading method, the activities of the catalysts were evaluated in terms of product composition and deoxygenation. The structure and acid site characteristics of the catalysts were analyzed by Brunauer-Emmett-Teller surface area measurement and NH₃ temperature-programmed desorption analysis. Catalytic upgrading reduced the amount of oxygenates in the product vapor due to the cracking reaction of the catalysts. Levoglucosan, a polymeric oxygenate species, was completely decomposed without being detected. While the amount of heavy phenols was reduced by catalytic upgrading, the amount of light phenols was increased because of the catalytic cracking of heavy phenols into light phenols and aromatics. The amount of aromatics increased remarkably as a result of catalytic upgrading, which is attributed to the strong Brönsted acid sites and the shape selectivity of the Meso-MFI catalyst. The addition of Pt made the Meso-MFI catalyst even more active in deoxygenation and in the production of aromatics.     

In-situ XAFS Analysis of Y Zeolite-Supported Rh Catalysts during High-Pressure Hydrogenation of CO2

In-situ XAFS (X-ray absorption fine structure) analysis under high-pressure, high-temperature reaction conditions was done to clarify the effect of Li doping on the structures of Rh species in Rh ion-exchanged NaY zeolite catalysts (RhY). The analysis showed that Rh species in RhY were reduced at a lower temperature than those in Li-doped RhY (Li/RhY). The reduction of Rh in RhY at a lower temperature was related to the formation of amorphous Rh oxide species during the initial stage of reduction, which was not observed in Li/RhY catalysts. The average particle size of metallic Rh species formed under the reaction conditions was 1.3 nm for RhY catalysts and 0.8 nm for Li/RhY catalysts. During exposure to either CO or air, the metallic Rh species in RhY were more easily subject to structural changes than the metallic Rh species in Li/RhY. These differences in the properties of Rh species between the RhY and Li/RhY catalysts resulted from the replacement of hydroxyl groups on the zeolite surface by O–Li compounds, and caused different catalytic activities during CO₂ hydrogenation.     

对羟基苯乙酮氨肟化制备对羟基苯乙酮肟

考察了在HTS-1分子筛催化剂上对羟基苯乙酮(简写为4-HAP)在固定床反应器中与氨和过氧化氢发生氨肟化反应合成对羟基苯乙酮肟(简写为4-HAPO)的反应规律,4-HAP氨肟化反应的适宜条件为:以乙醇为溶剂、温度高于60℃、反应时间大于5 h、4-HAP宜一次性加入、氨和过氧化氢连续加入、催化剂的质量分数为w(HTS-1)=1.4%、n(NH3)∶n(H2O2)∶n(4-HAP)=4.2∶1.1∶1、n(溶剂)∶n(4-HAP)=6∶1,4-HAP转化率达到73.9%,4-HAPO选择性达到98.9%,该结果优于类似条件下US 5 466 869报道的结果。通过色质联用分析鉴定了4-HAP氨肟化反应的产物,与现有的文献报道相比,HTS-1分子筛具有较高的活性和选择性,副产物的种类和数量均较少。4-HAP氨肟化反应过程中产生的副产物主要为1,8,9-蒽三酚(THA)和对苯二酚(HQ)。适当提高反应温度和催化剂浓度、提高氨与4-HAP的比例、控制过氧化氢与4-HAP在适当的摩尔比(如1.1∶1),可抑制这两种副产物的生成。HQ和1,8,9-蒽三酚在氨存在下发生氧化反应是反应产物颜色变深的原因。     

High effective dehydration of bio-ethanol into ethylene over nanoscale HZSM-5 zeolite catalysts

Nanoscale and microscale HZSM-5 zeolite catalysts were prepared and characterized by using SEM, XRD, IR, TPD and modified Hammett indicator method. Their performances in the dehydration of bio-ethanol into ethylene were compared in a fixed-bed reactor at 240 °C under atmospheric pressure. The results show that nanoscale HZSM-5 zeolite catalyst exhibits better stability than microscale HZSM-5 zeolite catalyst. When the 95(v) % bio-ethanol is used as the reactant, over nanoscale HZSM-5 catalyst, the conversion of bio-ethanol and the selectivity for ethylene almost keep constant during 630 h reaction, while over microscale HZSM-5 zeolite catalyst, the conversion of bio-ethanol decreases after 60 h reaction; in the case of the 45(v) % bio-ethanol employed as the feedstock, over nanoscale HZSM-5 catalyst, the conversion of bio-ethanol and the selectivity for ethylene almost keep constant during 320 h reaction, while over microscale HZSM-5 zeolite catalyst, both the conversion of bio-ethanol and the selectivity for ethylene decrease almost at the beginning of the reaction.     

t-Butylation of 1,2-dihydroxybenzene over acidic zeolites

t-Butylation of 1,2-dihydroxybenzene (DHB) with isobutene as alkylating agent was carried out over various acidic zeolites such as USH-Y, H-beta, and H-ZSM-5. USH-Y zeolite exhibits the highest catalytic activity and considerable selectivity of 4-t-butylcatechol (4-TBC). The selectivity of 4-TBC is increased in the order of H-ZSM-5>USH-YH-beta. 3-t-Butylcatechol (3-TBC) is well produced over catalyst with high SiO₂/Al₂O₃ ratio and large pore aperture. 3,5-Di-t-butylcatechol (3,5-DTBC) selectivity is maximum in zeolite which contains strong acidity and large pore channel. The influences of various reaction parameters such as reaction temperature, space velocity, reactant molar ratio are discussed. In order to improve 4-TBC formation and decrease in 3,5-DTBC selectivity simultaneously, USH-Y zeolite was silylated by tetraethylorthosilicate (TEOS) resulting in the decrease of 3,5-DTBC selectivity over modified catalysts by about 25%. USH-Y zeolite shows high stability in the t-butylation for at least 350 h. The coke formed during the reaction was identified by FT-IR and the USH-Y zeolite could be regenerated through oxidative thermal treatment.