• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Research on Catalytic Properties of Palladium Catalyst Prepared by Biological Reduction Method

    2013-07-25 10:07:38ZhangFengFuJiquan
    中國煉油與石油化工 2013年2期

    Zhang Feng; Fu Jiquan

    (School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing 100029)

    Research on Catalytic Properties of Palladium Catalyst Prepared by Biological Reduction Method

    Zhang Feng; Fu Jiquan

    (School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing 100029)

    This paper relates to highly dispersed supported Pd/MWCNTs and Pd/α-Al2O3catalysts prepared by biological reduction method. The physico-chemical properties and the difference in catalytic activity of Pd catalysts prepared by biological reduction method and chemical method, respectively, were investigated using XRD, TEM and specific surface characterization methods. The catalytic properties of catalysts were studied through activity evaluation means. The test results showed that the catalysts prepared by biological method were characteristic of small Pd nanoparticle size, good dispersion and low agglomeration, while possessing a high activity and stability in styrene hydrogenation reaction in comparison with catalysts prepared via the chemical method.

    Pd/MWCNTs; Pd/α- Al2O3; biological reduction; ginkgo leaf; Pd nanoparticles

    1 Introduction

    Catalyst with precision metal nanoparticles deposited on a support plays a dominant role in the field of oil refining, petrochemical industry and environmental protection thanks to its superior catalytic activity and selectivity. The traditional methods for preparing precious metal nanoparticles include physical method and chemical method. The catalyst preparation process using the physical method is simple, but the requirement on equipment is high and the production cost is expensive; the chemical method is flexible and diversified, but it should be realized with chemical reagents, which will bring about some environmental pollution problems. The biological reduction method for preparing precious metal nanoparticles is becoming a research focus in the field of nanometer scale technology along with the increasingly active research on greenization technology for preparation of materials[1]. Upon using biological method to prepare precious metal nanoparticles, there is no need to add additional chemical reagents, and pollution is reduced along with a full utilization of rich biological resources and biomass as the reducing agent[2-4]. Huang, et al.[5]prepared gold and silver nanoparticles through reduction using camphor leaf extract, and the addition of chemical reagent was not needed during the preparation process. Carbon nanotubes (CNTs) having good chemical stability and high specific surface area are the excellent support for active catalytic component[6-7]. The researchers have developed CNTs as the catalyst support that has been used in hydrogenation, dehydrogenation, and oxidation reactions[8-9]. The research on catalyst prepared by biological reduction method using carbon nanotubes as the support has not been reported previously.

    This study prepared a series of catalysts using ginkgo leaf extract as a reducing agent, with MWCNTs (multi-walled carbon nanotubes) and α-Al2O3serving as the support. The catalysts were characterized through XRD, TEM and specific surface area measurements, and the performance of catalysts was investigated through styrene hydrogenation to produce ethylbenzene for activity evaluation purposes.

    2 Experimental

    2.1 Preparation of extract

    Five gram of ginkgo leaf powder was added to a conical flask filled with 250 mL of deionized water. The conical flask was oscillated for 12 h at 60 ℃. Insoluble biomasswas removed by centrifugation after being cooled down. The obtained supernatant liquid was the ginkgo leaf extract at a concentration of 20 g/L, which was then stored in refrigerator at 4 ℃ prior to use.

    2.2 Preparation of catalyst

    A series of palladium catalysts supported on MWCNTs (including MWCNTs-0, Pd/MWCNTs-C, and Pd/ MWCNTs-B) and on α-Al2O3(including α-Al2O3-0, Pd/ α-Al2O3-C, Pd/α-Al2O3-B) were prepared respectively. Herein, 0 denotes the pure support (the pure support was prepared in order to study the influence of the said support on catalytic activity), C denotes the chemical method, and B denotes the biological method. A required concentration of palladium nitrate solution was prepared. An excess of palladium solution was used to impregnate multi-walled carbon nanotubes and α-Al2O3was used as the support for 6 h, followed by drying for 12 h at 60 ℃. Pd/MWCNTs-C catalyst and Pd/α-Al2O3-C catalyst were prepared by the chemical method. A certain amount of palladium nitrate solution was mixed with the same amount of ginkgo leaf extract. The excessive amount of the solution was used to impregnate multi-walled carbon nanotubes and α-Al2O3for 12 h. Thus, the Pd/MWCNTs-B catalyst and Pd/ α-Al2O3-B catalyst were prepared by the biological method after being dried for 24 h at 60 ℃. A series of catalysts using α-Al2O3as the support were calcined respectively for 2 h at 500 ℃, and were then reduced in the hydrogen flow.

    2.3 Characterization of catalysts

    The crystalline structure of catalysts was analyzed using a D8 Advance high-power X-ray diffractometer with a rotating target (made by the Bruker company), operating at a tube voltage of 40 kV, a tube current of 250 mA, a scan step size of 0.02°/step, and a scan range of 10°—90°. The morphology of catalysts was observed using a JOEL’s JEM2100 transmission electron microscope. The highresolution TEM images were obtained by a high magnif ication transmission electron microscope (JEM2100) at an accelerating voltage of 200 kV after dipping the ultra-thin carbon film in reaction solution followed by drying. Specific surface area and pore volume of each catalyst were measured by utilizing a pore distribution and specific surface measuring instrument made by the Beijing Jingweigaobo Science and Technology Development Center, with aP/P0in the range of 0.05—0.95.

    2.4 Evaluation of catalyst activity

    The reaction of styrene hydrogenation to form ethylbenzene was used as the probe reaction for evaluating the catalyst activity. The main reaction proceeds according to Formula (1), and this reaction only generates ethylbenzene under this condition, with the catalytic selectivity reaching 100%. 0.1 g of catalyst (with a particle size of 60-100 mesh) was weighed and added to the continuous micro-reactor device. H2flow was controlled at a rate of 80 ml/min, and the space velocity on catalyst was 20 h-1, with anhydrous ethanol used as solvent at a volume ratio of 1:1. The reaction temperature was 120 ℃, and sampling was performed at regular intervals. The composition of reaction products was analyzed by a GC-7890Ⅱ gas chromatography system (made by the Beijing Tianmei Instrument Company), equipped with a HJ-1 capillary column measuring Ф 0.25 mm×25 m and a FID detector, with the temperature in column equating to 100 ℃, in the sample room—200 ℃, and in the detection room—200 ℃. The content of each component was calculated by means of the area normalization method.

    3 Results and Discussion

    3.1 Characterization of catalysts

    3.1.1 XRD study

    Six prepared catalysts were characterized by XRD method in order to investigate whether the palladium loading could affect the structure of catalyst support and the crystalline structure of palladium on the catalyst.

    Figure 1 depicts XRD patterns of a series of catalysts supported on MWCNTs, and Figure 2 shows XRD patterns of a series of catalysts supported on α-Al2O3. It can be seen from the spectral line of MWCNTs-0 shown in Figure 1 that the diffraction peaks of crystal planes (002) and (101) in carbon nanotubes appear at 2θ=25.87° and 42.7°, respectively, while other peaks are not obvious. The dif-fraction peak of crystal plane (002) is wide, and its diffraction peak is high, suggesting that the degree of longrange order of nanostructure is poor. This may be caused by superposition of diffraction peaks of impurities such as amorphous carbon and graphite particles. It is known that the carbon nanotubes-supported Pd still retains the characteristics diffraction peaks of crystal planes (002) and (101) in carbon nanotubes and their diffraction peak intensity is relatively weak upon comparing the spectral lines of MWCNTs-0, Pd/MWCNTs-C and Pd/MWCNTs-B presented in Figure 1. These results indicated that the structure of carbon nanotubes was not destroyed, and could serve as excellent support of palladium. It can be learned from Figure 1 that Pd/MWCNTs-B has characteristics diffraction peaks of crystal planes (111), (200), (220) and (311) of Pd at 2θ of 40.06°, 46.59°, 68.13° and 82.11°, respectively upon comparing XRD patterns of Pd/ MWCNTs-C and Pd/MWCNTs-B. This has revealed that ginkgo leaf extract could reduce Pd2+ions to Pd0species, which were then deposited on the MWCNTs support. So ginkgo leaf extract is a good reducing agent for Pd2+ions. It can also be learned from XRD patterns that there was a diffraction peak of Pd0phase at 33.04°, indicating that a part of Pd0species was also deposited on the surface of MWCNTs. The reason was that the grain size of Pd0supported on the surface of MWCNTs was small, and it could be oxidized easily by the oxygen in air. So it could be reduced first in hydrogen stream before the commencement of catalytic reaction in the presence of Pd/MWCNTs catalyst.

    Figure 1 XRD patterns of MWCNT and Pd/MWCNTs catalyst samples

    Figure 2 XRD patterns of α-Al2O3and Pd/α- Al2O3catalyst samples

    It can be seen from the XRD patterns of Pd/α–Al2O3-C and Pd/α–Al2O3-B presented in Figure 2 that the supported Pd samples show characteristics diffraction peaks of crystal planes (111), (200) and (220) of Pd species at 2θ of 39.67°, 46.0° and 67.02°, respectively. This suggests that palladium species also existed in the form of single element on the surface of α–Al2O3support.

    3.1.2 TEM study

    XRD characterization confirmed that the palladium loading did not affect the structure of support, and palladium existed in the form of single element. TEM characterization was carried out in order to further study the surface morphology of the catalyst as well as the concentration and particle size of palladium particles.

    Figure 3 shows HRTEM images of Pd/MWCNTs catalysts. It can be seen from Figure 3 that the MWCNTs supported Pd species retain a good tubular morphology.

    Figure 3 HRTEM images of Pd/MWCNTs catalysts

    We can see from the HRTEM images by comparing Pd/ MWCNTs-C and Pd/MWCNTs-B that Pd nanoparticles are supported on the inner wall of MWCNTs in the Pd/ MWCNTs-C catalyst. However, the distribution of Pd nanoparticles is more uniform, and the Pd nanoparticles are supported on the outer and inner walls in the Pd/ MWCNTs-B catalyst prepared by the biological reduction method. It can be concluded that Pd nanoparticles had obvious lattice fringes as demonstrated by the highresolution lattice image of the Pd/MWCNTs-B catalyst. Thus, the formation of crystalline Pd was verified, which was consistent with the XRD characterization results. The particle size distribution of Pd nanoparticles existing in the form of single element in Pd/MWCNTs-B and Pd/ MWCNTs-C catalysts was calculated, with the results shown in Figure 5. We can see that when the particle size is small, the range of particle size distribution is narrow, and the average size of Pd particles is about 4 nm in the Pd/MWCNTs-B catalyst. We also can see that when the particle size is big, the range of particle size distribution is broader, and the average size of Pd particles is about 14.8 nm in the Pd/MWCNTs-C catalyst.

    Figure 4 shows HRTEM images of Pd/α-Al2O3catalyst. It can be seen from Figure 4 that α-Al2O3-supported Pd retains a good morphology. By comparing TEM images of Pd/α-Al2O3-C and Pd/α-Al2O3-B we can know that palladium nanoparticles supported on the surface of α-Al2O3can agglomerate to certain extent to form larger particles than that prepared by the biological method. However, palladium particle distribution in Pd/α-Al2O3-B catalyst prepared by the biological reduction method is more uniform and the particle is finer. This phenomenon may be attributed to the existence of biomass which makes the distribution of active components of catalyst more uniform during its preparation by the biological method, and Pd species exist in the form of single element in a reduced state. Thus, the agglomeration of active components was effectively avoided during the process of calcination. It should be noted that Pd supported on α-Al2O3at first existed in an ionic form, then turned to be single elemental Pd after calcination and reduction that took place in chemical immersion method. However, Pd was reduced directly on the support upon being treated by the biological reduction method. The two preparation methods were different in nature. It can be concluded that the supported Pd nanoparticles had obvious lattice fringes upon analyz-ing the high-resolution lattice images of Pd nanoparticles obtained by the biological reduction method. This outcome confirmed the existence of crystalline Pd, which was consistent with the XRD characterization results.

    Figure 4 HRTEM images of Pd/α- Al2O3catalysts

    Figure 5 Particle size distribution for supported Pd nanoparticles Frequency

    3.1.3 Specific surface area

    The specific surface area and pore volume of two series of catalysts were characterized, and the results are listed in Table 1.

    Table 1 BET surface area measurements

    It can be seen from Table 1 that the specific surface of catalyst samples varies to different extent ranging from 139.16 m2/g for support itself to 165.47 m2/g for catalyst prepared by the chemical method and 169.55 m2/g for catalyst prepared by the biological method due to the use of different methods for supporting palladium with MWCNTs. The reason is that the carbon nanotube is characteristic of a tubular structure. The overall specific surface of catalyst increases due to large specific surface area of the palladium particles that are deposited on inner and outer walls of the nanotubes. The specific surface area of catalyst prepared by the biological method was larger than that of catalyst prepared by the chemical method (as evidenced by comparison between Pd/MWCNTs-C and Pd/MWCNTs-B). The reason may be that Pd particles prepared by the biological method were larger in dimension, and were deposited on the inner and outer walls in a reduced state, leading to larger specific surface area. The pore volume of palladium catalyst with MWCNTs functioning as the support was smaller. This is because Pd particles supported on MWCNTs were embedded inside the carbon nanotubes, resulting in the blocking of a part of carbon nanotubes. Some carbon nanotubes were hollow, leading to the reduction of effective pore volume. This finding was consistent with the results shown by TEM measurements.

    For catalysts supported on α-Al2O3, the specific surface area of Pd/α-Al2O3-C prepared by the chemical method was 91.99 m2/g, which was lower than 102.42 m2/g for the α-Al2O3-0 support. However, the specific surface area of Pd/α-Al2O3-B prepared by the biological method was 149.66 m2/g, which was greater than the α-alumina support. This is probably because palladium particles prepared by the chemical method agglomerated on the surface of α-Al2O3during the process of calcination, and the particle size was greater, which blocked a part of the carbon nanotubes. The palladium nanoparticles supported on the surface were mainly in the form of single element on the Pd/α-Al2O3-B catalyst, and its particle size was small, which would not cause the blocking of nanotubes. The protective effect of biomass could be better utilized, so agglomeration would not easily take place during calcination. Due to large specific surface area of small particles, the overall specific surface area of the catalyst increased. The increase of pore volume was probably due to the acid etching effect of palladium nitrate solution (with a pH value of 1.0) on the surface of support during the process of impregnation, leading to an increased pore volume[10]. The pore volume of Pd/α-Al2O3-B was smaller compared with Pd/α-Al2O3-C due to the buffering effect of biomass, which could weaken the acid etching effect during the process of catalyst preparation by the biological method.

    3.2 Evaluation of catalyst activity

    Figure 6 Effect of reaction time on conversion of styrene

    The conversion of styrene during catalytic hydrogenation reaction on Pd/α-Al2O3-C and Pd/α-Al2O3-B catalysts is shown in Figure 6.It can be seen from Figure 6 that two catalysts have a high activity and stability in catalytic hydrogenation reaction of styrene. The activity of each catalyst is still high even after continuous reaction for 20 h. The catalytic performance of catalyst prepared by the biological method is better. The space velocity on styrene hydrogenation catalyst was increased from 20 h-1to 200 h-1in order to evaluate the catalytic activity of various catalysts. The activities of 6 catalyst samples were evaluated, and the results are shown in Figure 7. It can be seen from Figure 7 that the catalytic activity of catalysts varies significantly. The catalytic activity of MWCNTs-0 and Pd/α-Al2O3-0 comprising pure support is close to zero, indicating that pure support materials MWCNTs and α-Al2O3have no catalytic activity.

    Figure 7 Effect of different catalysts on conversion of styrene

    Upon comparing Pd/MWCNTs-C, Pd/MWCNTs-B and Pd/α-Al2O3-C and Pd/α-Al2O3-B catalysts, it can be learned that the catalytic activity of catalyst using MWCNTs as the support was higher than that of catalyst using α-Al2O3as the support, which might be probably attributed to the nanometer effect of carbon nanotubes. The structure of carbon nanotube itself provides a larger specific surface area, which significantly increases the support area and contributes to the uniform distribution of active component of catalyst. This view has already been demonstrated from previous characterizations. Therefore, the catalysts using MWCNTs as the support have a higher activity based on the same amount of catalyst support.

    The results showed that Pd/MWCNTs-C and Pd/ MWCNTs-B catalysts all had a higher activity with carbon nanotubes serving as the support. The high activity of these two catalysts identified at the beginning of reaction was resulted from the hydrogen reduction of catalysts. Pd/ MWCNTs-B catalyst began to show a much higher activity than that of Pd/MWCNTs-C catalyst in 2.5 h after the start of run. The reason is that the dispersion of palladium particles prepared by the biological reduction method was better, resulting in a uniform distribution of palladium on the inner and outer walls of carbon nanotubes with high stability. However, the stability of Pd/MWCNTs-C catalyst prepared by the chemical method was lower, which was consistent with the results obtained from TEM characterization. The activity of two catalysts all decreased due to the loss of active component with the extension of reaction time. Although the activity of both of them decreased, the activity of Pd/MWCNTs-B was slightly higher than that of Pd/MWCNTs-C after 2.5 h of reaction. In general, the activity of catalysts prepared by the biological method was higher than that of catalysts prepared by the chemical method.

    The activity of Pd/α-Al2O3-B catalyst prepared by the biological method was even higher than that of Pd/α- Al2O3-C catalyst prepared by the chemical method as indicated by the two curves of catalysts using α-Al2O3as the support.

    4 Conclusions

    1) MWCNTs containing no functional groups can be used as a good support for palladium catalyst. The MWCNT-supported catalyst had a higher activity compared with traditional Al2O3-supported catalyst, and had revealed considerable development potential.

    2) The biological reduction method using ginkgo leaf extract can directly reduce Pd2+ions to Pd0species. The biological method has the advantages of good dispersion, small particle size of active component and low agglomeration of Pd particles.

    3) Palladium catalysts prepared by the biological reduction method had higher activity and better stability than that of catalysts prepared by the chemical method under the reaction system adopted by this study.

    [1] Klefenz H. Nanobiotechnology: From molecules to systems[J]. Engineering in Life Science, 2004, 4(3): 211-218

    [2] Zheng Bingyun, Huang Jiale, Sun Daohua, et al. Research progress on biosynthetic technology of noble metal nanomaterials[J]. Journal of Xiamen University (Natural Science), 2011, 50(2): 378-386 (in Chinese)

    [3] Fu Jinkun, Liu Yueying, Fu Jinyin, et al. Preparation of supported palladium catalyst by biochemical method [J]. Journal of Xiamen University (Natural Science), 2000, 39(1): 67-71 (in Chinese)

    [4] Huang Jiale. Plant-mediated synthesis of silver and gold nanomaterials by biomass-based reduction and their potential applications[D]. Xiamen: Xiamen University, 2009 (in Chinese)

    [5] Huang J Y, Li Q B, Sun D, et al. Biosynthesis of silver and gold nanoparticles by novel sundried cinnamomum camphora leaf [J]. Nanotechnology, 2007, 18(10): 105104

    [6] Ye X R, Lin Y H, Wai C M. Decorating catalytic palladium nanoparticles on carbon nanotubes in supercritical carbon dioxide[J]. Chem Commun, 2003(5): 642-643

    [7] Yu R, Chen L, Liu Q, et al. Platinum deposition on carbon nanotubes via chemical modification[J]. Chem Mater, 1998, 10(3): 718-722

    [8] Li Xueting, Zang Pengyuan, Ye Qiuming, et al. Palladium on multi-walled carbon nanotubes (Pd/MWCNTs): Preparation and application in Heck reaction[J]. Chinese Journal of Inorganic Chemistry, 2011, 27(8): 1550-1554 (in Chinese)

    [9] Cao Youming, Wang Zhiyong. Preparation and catalytic properties of SWNTs-supported Pd catalyst[J]. Acta Phys-Chim Sin, 2009, 25(5): 825-828 (in Chinese)

    [10] Liu Huiping. Synthesis and characterization of novel mesoporous Al2O3and catalytic hydrogenation performance of Pt supported on mesoporous Al2O3[D]. Shanghai: East China University of Science and Technology, 2009 (in Chinese)

    Recieved date: 2013-01-31; Accepted date: 2013-03-30.

    Professor Fu Jiquan, Telephone: +86-10-64288291; E-mail: fujq010@sina.com.

    最近中文字幕高清免费大全6 | 日韩一本色道免费dvd| 日韩在线高清观看一区二区三区 | 色5月婷婷丁香| 国产亚洲精品av在线| 国产探花极品一区二区| 国产又黄又爽又无遮挡在线| 九九爱精品视频在线观看| 国产av一区在线观看免费| 国产日本99.免费观看| 久久久国产成人免费| 非洲黑人性xxxx精品又粗又长| 国产av一区在线观看免费| 亚洲午夜理论影院| 国产在线精品亚洲第一网站| 99久久精品一区二区三区| 又爽又黄a免费视频| x7x7x7水蜜桃| 成人午夜高清在线视频| 啪啪无遮挡十八禁网站| a级毛片免费高清观看在线播放| 精品一区二区免费观看| 少妇丰满av| 国产精品综合久久久久久久免费| 麻豆久久精品国产亚洲av| 午夜福利18| 国产三级在线视频| 熟女电影av网| 1000部很黄的大片| 亚洲电影在线观看av| h日本视频在线播放| 小说图片视频综合网站| 亚洲电影在线观看av| 又粗又爽又猛毛片免费看| 亚洲精品在线观看二区| 亚洲自拍偷在线| 久久久午夜欧美精品| 3wmmmm亚洲av在线观看| 亚洲精品成人久久久久久| 国产一区二区在线观看日韩| 精品一区二区免费观看| 免费高清视频大片| 精品久久久久久久久av| 日日干狠狠操夜夜爽| 亚洲黑人精品在线| 欧美zozozo另类| a在线观看视频网站| 久久久久国内视频| 精品一区二区三区视频在线| 午夜激情欧美在线| 久久精品国产99精品国产亚洲性色| 两人在一起打扑克的视频| 可以在线观看的亚洲视频| 真人一进一出gif抽搐免费| 日韩 亚洲 欧美在线| 一级黄片播放器| 女的被弄到高潮叫床怎么办 | 黄色女人牲交| 久久中文看片网| 91久久精品国产一区二区三区| 中文字幕熟女人妻在线| 天天躁日日操中文字幕| 在现免费观看毛片| 婷婷精品国产亚洲av| 国产激情偷乱视频一区二区| 国产乱人视频| 日韩欧美免费精品| 色av中文字幕| 在线天堂最新版资源| 免费电影在线观看免费观看| 免费观看的影片在线观看| 国产大屁股一区二区在线视频| 国产视频一区二区在线看| 日韩欧美一区二区三区在线观看| 好男人在线观看高清免费视频| 啦啦啦观看免费观看视频高清| 精品一区二区三区人妻视频| 精品久久国产蜜桃| xxxwww97欧美| 伦理电影大哥的女人| 亚洲精品成人久久久久久| 成人午夜高清在线视频| av在线老鸭窝| 一区二区三区高清视频在线| 在线观看美女被高潮喷水网站| 啦啦啦啦在线视频资源| 黄色日韩在线| 亚洲精品成人久久久久久| 我的女老师完整版在线观看| www.www免费av| 精品午夜福利视频在线观看一区| 亚洲人成网站在线播放欧美日韩| 床上黄色一级片| 可以在线观看的亚洲视频| 中文字幕av在线有码专区| av天堂在线播放| 欧美日韩乱码在线| av黄色大香蕉| 精品人妻偷拍中文字幕| 国产高清有码在线观看视频| 乱码一卡2卡4卡精品| 日本黄色视频三级网站网址| 国产精品自产拍在线观看55亚洲| 欧美高清性xxxxhd video| 国产精品亚洲一级av第二区| 变态另类丝袜制服| 91精品国产九色| 日韩精品中文字幕看吧| 亚洲av免费在线观看| 精品欧美国产一区二区三| 亚洲av中文字字幕乱码综合| www日本黄色视频网| 日本a在线网址| 欧美极品一区二区三区四区| 精品一区二区三区视频在线观看免费| 精品久久国产蜜桃| 欧美极品一区二区三区四区| 我的老师免费观看完整版| 女生性感内裤真人,穿戴方法视频| 99热6这里只有精品| 欧美绝顶高潮抽搐喷水| 久久久久久久久大av| 给我免费播放毛片高清在线观看| av在线亚洲专区| 亚洲成人中文字幕在线播放| 99久久精品国产国产毛片| 成人一区二区视频在线观看| 亚洲欧美日韩无卡精品| 午夜福利视频1000在线观看| 国产精品野战在线观看| 国产一区二区三区av在线 | 五月玫瑰六月丁香| 美女高潮的动态| 日韩精品中文字幕看吧| 国产黄a三级三级三级人| 久久久久性生活片| 又紧又爽又黄一区二区| a级毛片a级免费在线| 男人狂女人下面高潮的视频| 成人特级黄色片久久久久久久| 免费高清视频大片| 国产v大片淫在线免费观看| 成人国产综合亚洲| 免费高清视频大片| 亚洲av电影不卡..在线观看| 人妻夜夜爽99麻豆av| 综合色av麻豆| 别揉我奶头 嗯啊视频| 永久网站在线| 我要搜黄色片| 天堂网av新在线| 成人国产一区最新在线观看| 国产黄色小视频在线观看| 亚洲男人的天堂狠狠| 亚洲第一区二区三区不卡| 色综合站精品国产| 日韩欧美在线二视频| 亚洲一区二区三区色噜噜| 色综合站精品国产| 久久久久精品国产欧美久久久| 12—13女人毛片做爰片一| a级毛片免费高清观看在线播放| 91麻豆av在线| 国产高潮美女av| 亚洲av一区综合| 亚洲第一电影网av| 精品人妻1区二区| 最近最新免费中文字幕在线| 亚洲av中文字字幕乱码综合| 黄色女人牲交| 成人鲁丝片一二三区免费| 黄色日韩在线| 国产精品女同一区二区软件 | 国国产精品蜜臀av免费| 女人被狂操c到高潮| 黄色日韩在线| 久久久久久国产a免费观看| 国产单亲对白刺激| 久久精品91蜜桃| 俄罗斯特黄特色一大片| 久久精品国产鲁丝片午夜精品 | 特大巨黑吊av在线直播| 日本免费一区二区三区高清不卡| 久久天躁狠狠躁夜夜2o2o| 联通29元200g的流量卡| 九九久久精品国产亚洲av麻豆| 麻豆成人午夜福利视频| 成年版毛片免费区| 久久久久久大精品| 中文在线观看免费www的网站| 一进一出抽搐gif免费好疼| 欧美日韩乱码在线| 国产精品野战在线观看| 久久久成人免费电影| 日韩 亚洲 欧美在线| 成人国产综合亚洲| 乱人视频在线观看| 国产大屁股一区二区在线视频| 日日啪夜夜撸| 嫩草影院入口| 国产亚洲精品综合一区在线观看| 免费不卡的大黄色大毛片视频在线观看 | 日本一二三区视频观看| 色5月婷婷丁香| 国产精品av视频在线免费观看| 日本欧美国产在线视频| 国产成人一区二区在线| 国产av不卡久久| 精品午夜福利视频在线观看一区| 97碰自拍视频| 一个人观看的视频www高清免费观看| 日韩大尺度精品在线看网址| 亚洲成人中文字幕在线播放| 精品无人区乱码1区二区| 国产黄片美女视频| 天美传媒精品一区二区| 国产探花在线观看一区二区| 精品久久久久久久久亚洲 | 村上凉子中文字幕在线| 美女cb高潮喷水在线观看| 欧美日本视频| 日本精品一区二区三区蜜桃| 九九爱精品视频在线观看| 男女啪啪激烈高潮av片| 高清毛片免费观看视频网站| 久久久久久久久中文| 他把我摸到了高潮在线观看| 老司机福利观看| 成人毛片a级毛片在线播放| 成人午夜高清在线视频| 日日摸夜夜添夜夜添av毛片 | 色综合婷婷激情| 国产免费av片在线观看野外av| 一进一出抽搐动态| 波野结衣二区三区在线| 91久久精品国产一区二区三区| 精品久久久久久久久久久久久| 亚洲av中文av极速乱 | 欧美一区二区精品小视频在线| 女人十人毛片免费观看3o分钟| 大又大粗又爽又黄少妇毛片口| 亚洲成人中文字幕在线播放| 国产视频内射| 久久热精品热| 好男人在线观看高清免费视频| 国产精品国产高清国产av| 欧美一区二区国产精品久久精品| 国产精品一区二区免费欧美| 欧美日韩精品成人综合77777| 给我免费播放毛片高清在线观看| 又紧又爽又黄一区二区| 最近中文字幕高清免费大全6 | 亚洲av美国av| 欧美日韩亚洲国产一区二区在线观看| 日本与韩国留学比较| 禁无遮挡网站| 一级黄色大片毛片| 亚洲七黄色美女视频| 日日夜夜操网爽| 少妇丰满av| 亚洲欧美激情综合另类| 大型黄色视频在线免费观看| 最后的刺客免费高清国语| 熟妇人妻久久中文字幕3abv| 国产精品精品国产色婷婷| 日本一本二区三区精品| 99热网站在线观看| 蜜桃久久精品国产亚洲av| 日韩欧美 国产精品| av在线天堂中文字幕| 久久久精品大字幕| 97超视频在线观看视频| 国产av一区在线观看免费| 精品久久久久久,| 欧美色视频一区免费| 国语自产精品视频在线第100页| 久久久精品欧美日韩精品| 午夜精品一区二区三区免费看| 最新中文字幕久久久久| 亚洲av不卡在线观看| 成人国产一区最新在线观看| 亚洲最大成人手机在线| 一区二区三区激情视频| 欧美激情在线99| 中文字幕av在线有码专区| 亚洲自偷自拍三级| 国产大屁股一区二区在线视频| 黄片wwwwww| 很黄的视频免费| 国产午夜福利久久久久久| 91久久精品国产一区二区成人| 国产亚洲精品av在线| 99在线人妻在线中文字幕| 又爽又黄a免费视频| www日本黄色视频网| 免费在线观看成人毛片| 男人舔奶头视频| 久久九九热精品免费| 亚洲经典国产精华液单| 欧美激情在线99| 国产午夜精品论理片| 久久久久久久午夜电影| 窝窝影院91人妻| 亚洲av美国av| 亚洲人成网站高清观看| 亚州av有码| 高清在线国产一区| 国产精品av视频在线免费观看| 久久草成人影院| av天堂在线播放| 国产精品美女特级片免费视频播放器| 国产女主播在线喷水免费视频网站 | 日本爱情动作片www.在线观看 | 日日啪夜夜撸| 在线看三级毛片| 亚洲专区中文字幕在线| 18禁黄网站禁片午夜丰满| av.在线天堂| 校园人妻丝袜中文字幕| 午夜免费男女啪啪视频观看 | 国产成人av教育| 一区二区三区激情视频| 午夜福利视频1000在线观看| 国产精品久久久久久久电影| 午夜福利视频1000在线观看| 国产极品精品免费视频能看的| 国产精品久久视频播放| 日本成人三级电影网站| 久久久久九九精品影院| 亚洲成人免费电影在线观看| 男人的好看免费观看在线视频| 网址你懂的国产日韩在线| 一区二区三区四区激情视频 | 国产精品野战在线观看| 亚洲av日韩精品久久久久久密| 午夜精品一区二区三区免费看| 国产精品免费一区二区三区在线| 国产大屁股一区二区在线视频| 国产免费av片在线观看野外av| 亚洲人成网站在线播| 91av网一区二区| 成人二区视频| 精品久久久久久久久亚洲 | 久久久久久久久久黄片| 久久国产精品人妻蜜桃| 99热只有精品国产| 亚洲人成网站高清观看| 国产国拍精品亚洲av在线观看| 国产精品一区二区免费欧美| 亚洲av成人av| 日日摸夜夜添夜夜添小说| 亚洲熟妇中文字幕五十中出| 人妻丰满熟妇av一区二区三区| 国产成年人精品一区二区| 直男gayav资源| 婷婷六月久久综合丁香| 中文在线观看免费www的网站| 免费av毛片视频| 国产精品永久免费网站| 久久久久久伊人网av| 精品久久久久久久久久久久久| 国产蜜桃级精品一区二区三区| 99热这里只有精品一区| www.色视频.com| 久久精品国产鲁丝片午夜精品 | 波多野结衣巨乳人妻| 男女边吃奶边做爰视频| 日韩 亚洲 欧美在线| 日韩人妻高清精品专区| 欧美色欧美亚洲另类二区| 午夜免费成人在线视频| 一级黄片播放器| 亚洲精品在线观看二区| 美女高潮的动态| 国产精品无大码| 老司机午夜福利在线观看视频| 日韩欧美精品v在线| 色视频www国产| 无遮挡黄片免费观看| 国产视频内射| 3wmmmm亚洲av在线观看| 国内久久婷婷六月综合欲色啪| 99热网站在线观看| 亚洲欧美日韩高清在线视频| 国产国拍精品亚洲av在线观看| 成人欧美大片| 国产精品爽爽va在线观看网站| 久久久久久久久中文| 久久久精品欧美日韩精品| 搡老熟女国产l中国老女人| 欧美一区二区亚洲| 欧美日韩瑟瑟在线播放| 欧美xxxx黑人xx丫x性爽| 女同久久另类99精品国产91| 亚洲欧美日韩高清专用| 久久精品人妻少妇| 久久99热6这里只有精品| 深夜a级毛片| 成人亚洲精品av一区二区| 男人舔女人下体高潮全视频| 国产大屁股一区二区在线视频| 美女高潮喷水抽搐中文字幕| 国产精品野战在线观看| 欧美一区二区亚洲| 免费无遮挡裸体视频| 欧美黑人巨大hd| 九九在线视频观看精品| 最近在线观看免费完整版| 99久久久亚洲精品蜜臀av| 成人性生交大片免费视频hd| 自拍偷自拍亚洲精品老妇| 蜜桃亚洲精品一区二区三区| www.色视频.com| 国产成人a区在线观看| 哪里可以看免费的av片| 日韩欧美在线乱码| 两个人视频免费观看高清| 精品福利观看| 一本久久中文字幕| 12—13女人毛片做爰片一| 中文字幕精品亚洲无线码一区| 亚洲乱码一区二区免费版| 特大巨黑吊av在线直播| 我的女老师完整版在线观看| av专区在线播放| 狂野欧美激情性xxxx在线观看| 亚洲无线观看免费| 99久久无色码亚洲精品果冻| 999久久久精品免费观看国产| 国产欧美日韩一区二区精品| 婷婷精品国产亚洲av在线| 欧美丝袜亚洲另类 | h日本视频在线播放| 啪啪无遮挡十八禁网站| 精品一区二区三区视频在线观看免费| 国产精品一区www在线观看 | 最近最新中文字幕大全电影3| 国产精品一区二区三区四区久久| 日韩在线高清观看一区二区三区 | 在线国产一区二区在线| 日韩欧美免费精品| 三级男女做爰猛烈吃奶摸视频| 男插女下体视频免费在线播放| 国内精品美女久久久久久| 三级毛片av免费| 日本与韩国留学比较| 一卡2卡三卡四卡精品乱码亚洲| 色综合亚洲欧美另类图片| 天堂网av新在线| 国产精品爽爽va在线观看网站| 伊人久久精品亚洲午夜| 亚洲va在线va天堂va国产| 身体一侧抽搐| 欧美丝袜亚洲另类 | 亚洲av不卡在线观看| 久久久久久伊人网av| 亚洲三级黄色毛片| 免费大片18禁| 国产精品98久久久久久宅男小说| 精品一区二区三区视频在线| 国产精品无大码| 日本在线视频免费播放| 亚洲18禁久久av| 午夜视频国产福利| 欧美激情在线99| 亚洲电影在线观看av| 51国产日韩欧美| 少妇人妻一区二区三区视频| 级片在线观看| 成年女人永久免费观看视频| 欧美绝顶高潮抽搐喷水| 18禁裸乳无遮挡免费网站照片| 午夜福利高清视频| 91精品国产九色| 高清日韩中文字幕在线| 人人妻人人看人人澡| 99国产精品一区二区蜜桃av| 亚洲第一区二区三区不卡| x7x7x7水蜜桃| 黄色女人牲交| 国产精品电影一区二区三区| 亚洲av第一区精品v没综合| av天堂中文字幕网| 成人av在线播放网站| 午夜影院日韩av| 国内久久婷婷六月综合欲色啪| 变态另类丝袜制服| 少妇熟女aⅴ在线视频| 春色校园在线视频观看| 亚洲av中文av极速乱 | 哪里可以看免费的av片| 伊人久久精品亚洲午夜| 亚洲四区av| 99国产极品粉嫩在线观看| 九九爱精品视频在线观看| АⅤ资源中文在线天堂| 国产精品乱码一区二三区的特点| 男插女下体视频免费在线播放| 神马国产精品三级电影在线观看| 亚洲人成网站在线播| 十八禁网站免费在线| 国产午夜精品论理片| 国模一区二区三区四区视频| 中文字幕av成人在线电影| 欧美极品一区二区三区四区| 天堂√8在线中文| 国产伦在线观看视频一区| 久久久久国内视频| 亚洲精品在线观看二区| 又爽又黄a免费视频| 欧美性猛交黑人性爽| 精品福利观看| 欧美xxxx性猛交bbbb| 精品久久久久久久久亚洲 | 观看美女的网站| 在线天堂最新版资源| 日本撒尿小便嘘嘘汇集6| www.色视频.com| 久久久久久久久中文| 欧美成人a在线观看| 亚洲专区中文字幕在线| 亚洲精品乱码久久久v下载方式| 久久精品影院6| 国产精品乱码一区二三区的特点| 亚洲欧美日韩高清专用| 婷婷色综合大香蕉| 人妻丰满熟妇av一区二区三区| 校园人妻丝袜中文字幕| 三级国产精品欧美在线观看| 欧美成人免费av一区二区三区| 欧美精品国产亚洲| 亚洲最大成人中文| 别揉我奶头~嗯~啊~动态视频| 少妇人妻一区二区三区视频| 国内精品久久久久精免费| 一夜夜www| 麻豆久久精品国产亚洲av| 91麻豆av在线| 亚洲内射少妇av| 免费无遮挡裸体视频| bbb黄色大片| avwww免费| 真人做人爱边吃奶动态| 国产精品久久视频播放| 午夜免费成人在线视频| 久久人妻av系列| 亚洲av一区综合| 国产一级毛片七仙女欲春2| 又爽又黄无遮挡网站| 天堂动漫精品| 日韩精品中文字幕看吧| 欧美xxxx性猛交bbbb| 色综合亚洲欧美另类图片| 国产精品不卡视频一区二区| 99久久精品国产国产毛片| 精品人妻视频免费看| 日韩大尺度精品在线看网址| 亚洲国产精品成人综合色| 大型黄色视频在线免费观看| 精品久久久久久久久久久久久| 极品教师在线免费播放| 精品一区二区三区视频在线观看免费| 99久国产av精品| 国产av不卡久久| 国产乱人伦免费视频| 亚洲人成伊人成综合网2020| 美女黄网站色视频| 国产精品99久久久久久久久| 精品一区二区三区视频在线| 成人国产麻豆网| 国产在线男女| 俺也久久电影网| 91av网一区二区| 日日摸夜夜添夜夜添小说| 久久午夜福利片| 婷婷精品国产亚洲av在线| 国产高清三级在线| 69人妻影院| 一进一出抽搐gif免费好疼| 日韩欧美在线二视频| 最近视频中文字幕2019在线8| 亚洲电影在线观看av| 中出人妻视频一区二区| 国产一区二区激情短视频| 国产高清不卡午夜福利| 国产视频内射| 亚洲av成人av| 免费av不卡在线播放| 97超级碰碰碰精品色视频在线观看| 深夜精品福利| 亚洲国产精品合色在线| 三级毛片av免费| 97超视频在线观看视频| 黄色一级大片看看| 国产成人av教育| 99热只有精品国产| 少妇高潮的动态图| 国产成人av教育| 美女高潮喷水抽搐中文字幕| 少妇高潮的动态图| 久久久久性生活片| 国产欧美日韩精品亚洲av| 欧美不卡视频在线免费观看| 亚洲人成伊人成综合网2020| 深夜精品福利| 国产乱人伦免费视频| 国产69精品久久久久777片| 变态另类丝袜制服| 国产精品亚洲一级av第二区| 亚洲欧美精品综合久久99| 久久精品综合一区二区三区| av.在线天堂| 九九爱精品视频在线观看| 日韩欧美免费精品| 中文字幕av成人在线电影|