Enhanced selectivity and formation of ethylbenzene for acetophenone hydrogenation by adsorbed oxygen on Pd/SiO2

The effect of adsorbed oxygen for selectivity of acetophenone (AP) hydrogenation on Pd/SiO₂ catalyst at 298 K has been studied by means of gas phase acetophenone hydrogenation, infrared (IR) spectra, and temperature-programmed desorption. Acetophenone hydrogenation on reduced Pd/SiO₂ catalyst reveals a typical series reaction in which phenylethanol (PE) is the intermediate for ethylbenzene (EB) formation. The selectivity of the reaction is towards phenylethanol at low temperature. The oxidized Pd/SiO₂ catalyst exhibits very different catalytic selectivity with reduced catalyst. The selectivity of ethylbenzene can be significantly boosted to over 90%, even if the reaction approaches zero conversion, suggesting that phenylethanol needs not be an intermediate for production of ethylbenzene from acetophenone. The formation of ethylbenzene and phenylethanol on oxidized Pd may be controlled by a parallel reaction pathway. The numbers of adsorbed oxygen on Pd surface strongly dominate the rate of EB formation. The bulk Pd oxide cannot be reduced by hydrogen at 298 K, so the oxygen atoms in Pd bulk act a poison for AP hydrogenation, leading to deactivation of oxidized Pd catalyst. The adsorbed oxygen on Pd surface plays the important role that can activate the C---H bond of CH₃ group in acetophenone, leading to the formation of a new intermediate (perhaps acetophenone enolate). This intermediate is the key species that will be further hydrogenated to ethylbenzene.     

Desorption study of NO and O2 on Cu-ZSM-5

A detailed temperature-programmed desorption (TPD) study on NO and O₂ saturated Cu-ZSM-5 at different temperatures (300–723 K) has been performed. In the temperature range 373–723 K, the evolution of O₂ and NO₂ accompanying the desorption of NO from NO saturated Cu-ZSM-5 suggested the formation of nitrite/nitrate species. The amount of O₂ absorbed was very much lower than that of NO. The desorption profile of O₂ after contacting Cu-ZSM-5 with O₂ at 623 K showed a low temperature peak (369K) confirming the spontaneous ability of O₂ desorption from copper zeolite. Moreover, successive saturation cycles of NO followed by O₂ and vice versa have been performed at various temperatures (298–623 K) to understand the modifications which the adsorption sites undergo when the two molecules NO and O₂ are available together for adsorption on the catalyst sites. After each saturation cycle, a TPD profile was recorded following the evolution of NO, O₂ and other NO_x species. The competitive adsorption experiments revealed that, at 623 K, NO was not able to successfully compete with O₂ for the adsorption sites, therefore the adsorption of NO at 623 K on O₂ saturated catalyst was not completely restored. On the basis of the experimental work, an overall adsorption reaction scheme of NO on Cu-ZSM-5 was proposed     

烧结温度对SiO2-TiO2薄膜亲水性的影响

为了确定SiO2-TiO2薄膜制备过程的最佳烧结温度,将不同SiO2与TiO2掺杂比的样品分别在400℃和500℃下煅烧,进行与水的静态接触角测试。结果表明,在一定掺杂比范围内,SiO2的掺杂能明显提高TiO2表面亲水性,并且500℃煅烧的产品亲水性要好于400℃煅烧的产品。SEM和XRD表明,500℃煅烧的产品表面颗粒粒径要大于400℃煅烧的产品的表面颗粒粒径,并且已有了比较明显的锐钛矿晶型特征峰,而400℃煅烧的产品还是无定形态,这说明SiO2的掺杂抑制了TiO2晶粒的生长和晶型的转变。而锐钛矿晶型的TiO2亲水性要远好于无定形的TiO2,致使500℃煅烧的产品的亲水性要好于400℃煅烧的产品的亲水性,因此500℃才是SiO2-TiO2薄膜的最佳烧结温度。     

Characterization and photocatalytic activity of transition-metal-supported surface bond-conjugated TiO2/SiO2

TM/TiO₂/SiO₂ photocatalysts were prepared by the photodeposition method using transition metal salts (TM=Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺) as precursors and the surface bond-conjugated TiO₂/SiO₂ as supporter in N₂ atmosphere, and were characterized by XRD, XPS, UV-Vis diffuse reflection and zeta-potential. Their photocatalytic activities were evaluated using reactive brilliant red K-2G (K-2G) and cationic blue X-GRL (CBX) showing different adsorption behavior on the oxides. Fe, Cu supported TiO₂/SiO₂ can efficiently extend the light absorption to the visible region. XPS analysis verified that the introduction of transition metal lead to the changes of the electronic environmental of Ti cations and the zeta-potential of oxides. As a result, K-2G has higher adsorption on the modified TiO₂/SiO₂ than that on the baked one, while the adsorption of CBX has a little change on the both oxides. At the same time, for the photodegradation of K-2G, Fe³⁺, Co²⁺, Ni²⁺-modified catalysts show that their photoactivities are 3.3–2.2 times higher than the bare one. On the contrast, all transition-metal-supported catalysts have no significant activity improvement except that Fe/TiO₂/SiO₂ shows 1.68 times higher activity for the photodegradation of CBX. The results indicate that the photoactivity could be increased in photodegradation of dyes by changing the performances of adsorption to dyes and absorption to light of photocatalyst.     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

二氧化硅超细短纤维/氯丁橡胶复合材料的结构与性能

利用静电纺丝技术制备二氧化硅超细短纤维(n-SF),采用偶联剂KH-570对其进行改性,再制备改性n-SF(n-MSF)/氯丁橡胶(CR)复合材料,并对复合材料的结构和性能进行研究。结果表明:n-MSF在CR基体中分散均匀,与CR界面结合良好;加入适量的n-MSF,复合材料的定伸应力、撕裂强度及抗溶胀能力明显提高,动态力学性能有所改善。     

Conversion of propylene into cyclohexane on PtGaZr/SiO2 catalyst

The light olefins present in Delay Coker and fluid catalytic cracker dry gas can be valorized into naphthenes using a new PtGaZr/SiO₂ catalyst. This catalyst was compared to a GaZrSiO₂ catalyst prepared with the same methodology. Both were characterized by XRD, and FTIR, XPS, ⁷¹Ga, ²⁹Si and ¹H NMR spectroscopies. Propylene is treated in the presence of CS₂, hydrogen, and benzene in a semi-batch type reactor and the product composition is analyzed by GC and MS techniques. The different operating variables were explored to study the effect of Pt on activity, selectivity and catalyst stability. The spent catalysts after 10 cycles in operation were analyzed using ¹³C NMR, ¹H NMR, IR, and XPS spectroscopies. The paper discusses the catalytic surface composition, the effect of temperature, contact time, hydrogen partial pressure and benzene in the feed. The study demonstrated that the effect of Pt, hydrogen and benzene is crucial to orient the reaction toward naphthenes production.     

Immobilization of manganese tetraphenylporphyrin on Au/SiO2 as new catalyst for cyclohexane oxidation with air

Manganese tetraphenylporphyrin was successfully immobilized on Au/SiO₂, by using mercaptopyridine with sulfhydryl and pyridyl groups as bridging agent. The synthesized catalyst with novel structure was characterized by FTIR spectroscopic technique, XPS measurement, TG–DTA analysis and so on. During aerobic oxidation of cyclohexane in the presence of this material, the conversion of cyclohexane and total selectivity to cyclohexanone and cyclohexanol were up to 5.39% and 88.74%, respectively.     

Characterization and reactivity of MoO3/SiO2 catalysts in the selective catalytic oxidation of ammonia to N2

Silica-supported MoO₃ catalysts with MoO₃ loadings up to 21% w/w were prepared, characterized and tested in the selective catalytic oxidation (SCO) of ammonia to N₂ under dilute conditions. It is found that the catalysts are active and selective in the reaction, and that the catalytic performance increases on increasing the Mo loading. Crystalline MoO₃, detected over the silica support, is supposed to be the active species in the reaction. The reactivity of the catalysts is depressed by water addition to the feed at low temperatures and is enhanced by the presence of selected promoters, like Bi and Pb.     

改善耐热性的聚乳酸/纳米SiO_2共混母粒的制备及性能

利用双螺杆挤出机制备了耐热性得到改善的聚乳酸/SiO2共混母粒,研究了母粒制备工艺,并采用扫描电镜对母粒的结构进行分析,采用熔融指数表征母粒的可纺性,采用热失重、差示扫描量热法对母粒的热性能进行分析。结果表明:纳米SiO2颗粒在聚乳酸中分散均匀,共混母粒可纺性好,分解温度提高,玻璃化转变温度及其热焓也有提高,因而聚乳酸的耐热性得以改善。     

NH3-TPD and XPS studies of Ru/Al2O3 catalyst and HDS activity

The effects of pretreatment of catalyst on its surface properties and the HDS activity of a 0.49% Ru/Al₂O₃ catalyst were studied in a single-pass, differential microreactor. The surface properties of the catalyst were measured by NH₃-TPD and XPS analysis. The Ru/Al₂O₃ catalyst was pretreated in three ways: reduced in H₂ (Ru-R catalyst), oxidized in air and subsequently reduced in H₂ (Ru-OR catalyst), or sulfided in H₂S/H₂ (Ru-S catalyst). Three types of peaks (low, middle, and high temperatures) were observed in the NH₃-TPD study. The predominant high-temperature peak was observed for both the Ru-OR and Ru-S catalyst, pretreated at 300°C. Mass spectrometry showed that the high-temperature peak in NH₃-TPD consisted of N₂ and H₂ formed from the decomposition of NH₃ on the ruthenium sites. NO adsorption of unsaturated Ru species was related to the low-temperature peak in the NH₃-TPD. The XPS analysis showed that the peaks at 279.9 eV, 280.6 eV, and 282.5 eV were ascribed to metallic ruthenium, RuO₂, and RuO₃, respectively. The low-, middle-, and high-temperature peaks were assigned to RuO₂, acid sites on alumina, and metallic Ru, respectively. Metallic ruthenium was effective in the HDS of thiophene and the decomposition of NH₃.     

SiO2/Al2O3对仿铜金属光泽釉面的性能影响

通过单因素实验探讨了SiO2/Al2O3摩尔比对仿铜金属釉的影响,研制了一种釉面耐磨性较高且呈现仿铜金属效果的生料金属釉。实验结果表明:随着SiO2/Al2O3摩尔比的增加,由于釉中析出的晶体种类和数量不同,从而导致釉面光泽度和色泽不一。当SiO2/Al2O3摩尔比为5.6时,釉中析出了CuMn2O4尖晶石晶体,从而使釉面呈现最佳的仿铜金属光泽,该釉面硬度为894.65Kg/mm2。     

Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts

A series of SAPO-34 molecular sieves with different SiO₂/Al₂O₃ ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N₂ adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO₂/Al₂O₃ ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO₂/Al₂O₃ ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Br?nsted and Lewis acid sites and Br?nsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO₂/Al₂O₃ ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed.     

Synthesis of nanosized TiO2/SiO2 particles in the microemulsion and their photocatalytic activity on the decomposition of p-nitrophenol

Nanosized pure TiO₂ particles were prepared by hydrolysis of TTIP in the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles. TiO₂/SiO₂ nanoparticles were also prepared from TEOS as a silicon source and TTIP as a titanium source. These particles were characterized by TEM, XRD, FT-IR, BET, TGA and DTA. From thermal analysis and XRD analysis, the anatase structure of pure titania appeared in the 300–600 °C calcination temperature range and the rutile structure was showed above 700 °C. However, no rutile phase was observed for the TiO₂/SiO₂ particles up to 800 °C. The crystallite size decreased and the surface area of TiO₂/SiO₂ particles monotonically increased with an increase of the silica content. From FT-IR analysis, the band for Ti–O–Si vibration was observed and the band intensity for Si–O–Si vibration increased with an increase of the silica content. The micrographs of TEM showed that the TiO₂/SiO₂ nanoparticles had a spherical and a narrow size distribution. In addition, TiO₂/SiO₂ particles showed higher photocatalytic activity than pure TiO₂ and the TiO₂/SiO₂ (90/10) particles showed the highest activity on the photocatalytic decomposition of p-nitrophenol.     

Cu/SiO2催化剂载体预处理工艺的研究

对硝基苯加氢制苯胺Cu/SiO₂催化剂载体的预处理工艺进行研究,考察预处理工艺条件对硅胶孔结构的影响。对经过预处理和未经过预处理的载体制备的催化剂活性进行对比测试,结果表明,预处理载体制备的催化剂,保持高转化率的时间较未经预处理载体制备的催化剂保持高活性的时间长,说明载体经过预处理制备的催化剂达到了延长使用寿命的效果。     

Aerobic oxidation of alcohols over Au/TiO2: An insight on the promotion effect of water on the catalytic activity of Au/TiO2

The unique and significant promotion effect of water has been evidenced by the selective oxidation of benzyl alcohol to benzaldehyde over Au/TiO₂ catalysts. Water has dual promotional functions in the reaction system: to help form unique microdroplets in a multiphase reaction system and to assist the oxygen adsorption and activation. The conversion of benzyl alcohol at a molar ratio of water to solvent (p-xylene) of 7 is 7 times higher than in the absence of water. The present work has highlighted the potential of Au/TiO₂ catalysts in aerobic oxidation of alcohols in the unique multiphase reaction system with water as promoting solvent.     

Structures of H3PO4/SiO2 catalysts and catalytic performance in the hydration of ethene

The hydration of ethene was carried out over H₃PO₄/SiO₂ having various amounts of H₃PO₄. The rate of the ethanol formation increased markedly with the increasing H₃PO₄ loadings, in particular above 60–70 wt%. By X-ray diffraction (XRD), and

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MAS NMR methods, it was revealed that various silicon phosphates were produced in the preparation of the catalysts. The structures of the phosphates depended on the H₃PO₄ loadings. It was suggested that Si(HPO₄)₂·H₂O species which formed at higher H₃PO₄ loadings were hydrolyzed to H₃PO₄ and SiO₂ during the course of the reaction, yielding the catalysts with high performance. The bulk phase of the H₃PO₄ was involved in the reaction.     

Na/SiO2新型固体碱催化制备生物柴油的研究

以NaOH、正硅酸乙酯和乙醇为原料,经溶胶-凝胶法制备新型固体碱催化剂（Na/SiO₂）,用于催化大豆油与甲醇的酯交换反应制备生物柴油,研究催化剂焙烧温度、n(NaOH)∶n(SiO₂)、n(甲醇)∶n(大豆油)、催化剂用量和反应时间对产率的影响以及催化剂的稳定性。结果表明,固体碱催化剂Na/SiO₂在大豆油与甲醇的酯交换反应中具有较高的催化活性,在催化剂焙烧温度600 ℃、n(NaOH)∶n(SiO₂)=2∶1、n(甲醇)∶n(大豆油)=15∶1、催化剂用量为大豆油质量的7%和反应时间3 h的条件下,脂肪酸甲酯产率可达97.42%,催化剂在稳定性试验中呈现出优良的稳定性。     

DRIFT study of temperature programmed desorption of NO adsorbed on Co–Mo/Al2O3 sulfided at high pressure

In order to make clear the coordinatively unsaturated sites (CUS) of Co–Mo/Al₂O₃ sulfided at high pressure, the temperature programmed desorption of NO adsorbed on Co–Mo/Al₂O₃ sulfided at high pressure was studied by DRIFT method. The intensity of two IR bands (1835 and 1785 cm⁻¹) of adsorbed NO on Co–Mo/Al₂O₃decreased simultaneously up to 393 K. The higher frequency band disappeared at 393 K, while the lower frequency band remained even at 403 K. In the case of Mo/Al₂O₃, the intensities of two bands appeared at 298 K decreased monotonously with increasing temperature, and disappeared simultaneously over 433 K. In the case of Co/Al₂O₃, two bands disappeared simultaneously over 393 K. These results suggest that two kinds of nitrosyl species are formed on Co–Mo/Al₂O₃. One is dinitrosyl species adsorbed on CUS of Co, and the other is unidentified nitrosyl species. Comparing DRIFT spectra of Co–Mo/Al₂O₃ with those of a physical mixture of Mo/Al₂O₃ and Co/Al₂O₃, it is also suggested that the formation of the latter one correlates with the interaction between Co and Mo in Co–Mo/Al₂O₃. The unidentified nitrosyl species might be the key to explain the dependency of DRIFT spectrum of adsorbed NO on the pressure of sulfiding.     

高岭土原位合成高硅铝比小晶粒NaY分子筛

以不同温度焙烧的苏州高岭土为原料,采用原位晶化法合成高硅铝比小晶粒NaY分子筛,考察晶种胶添加量、陈化温度、晶化温度和m(高土)∶m(偏土)对晶化过程和产物性质的影响。结果表明,m(高土)∶m(偏土)=1时,在晶种胶添加质量分数15%、陈化温度90℃和晶化温度100℃条件下,以普通高岭土为原料原位合成NaY样品的相对结晶度约为80%,骨架硅铝比(SiO2与Al2O3物质的量比)为6.4,平均粒径约500nm。调整原料中m(高土)∶m(偏土)可以控制原位晶化样品中的分子筛含量。以细化高岭土为原料合成的NaY分子筛(平均约445nm)粒径小于普通高岭土合成的样品。骨架硅铝比高于6.0的原位晶化样品的骨架坍塌温度高于950℃,具有很高的结构稳定性。