CO低温氧化Au/Al2O3催化剂的失活及稳定性

 采用改进的等体积浸渍法制备了1.5%Au/Al2O3催化剂,考察了催化剂在CO低温氧化反应中的催化活性,比较了其在干燥的原料气和水汽饱和的原料气中的稳定性,考察了经水汽饱和或加热的空气处理后催化剂活性的变化,探讨了催化剂失活的原因. 结果表明, Au/Al2O3在水汽饱和的原料气中比在干燥的原料气中具有更好的稳定性,经水汽饱和或加热的空气处理后其活性均会下降. Au/Al2O3的失活主要包括CO氧化失活、热处理失活和水汽处理失活,前两种失活主要是因为催化剂中类似碳酸盐物种的生成和活性位上-OH 的脱除,是可逆失活; 而最后一种失活是不可逆的,主要归因于金颗粒的长大.     

一步合成二甲醚催化剂烧结失活和原位再生的研究

采用共沉淀沉积法制备了CuOZnOAl2O3/γ Al2O3 HZSM 5复合催化剂,考察了其对CO加氢直接合成二甲醚的催化性能,研究了催化剂的失活和再生,并用H2-TPR、XRD、TPO、N2O化学吸附等表征方法对反应前后和再生后催化剂的物化性质进行了表征。结果表明,一步合成二甲醚催化剂的失活主要是由于活性位Cu晶粒的烧结长大;反应温度和原料气的组成是影响催化剂失活的因素,在低于220℃下,以N2/H2/CO/CO2为原料气会显著降低催化剂的失活速率。研究使用的氧化还原循环的再生方法能够使Cu晶粒发生再分散,并使失活的催化剂恢复了75%以上的活性。     

预处理条件对Au/Al2O3催化CO氧化性能的影响

 采用沉积-沉淀法制备了Au/Al2O3,探讨了预处理条件对催化剂中金颗粒的大小及其催化CO氧化性能的影响,并以XRD和TEM等手段对催化剂进行了结构表征. 结果表明,还原和焙烧预处理得到的1.2% Au/Al2O3催化剂在GHSV=1.5×104 h-1时,可分别于-22和-10 ℃将空气中的1%CO完全氧化, 还原预处理所得催化剂的活性更高, 原因是催化剂中金颗粒的尺寸更小,分散度更高.     

Ru-La2O3/γ-Al2O3催化剂合成、表征及CO选择性氧化

采用浸渍法制备了系列Ru-La2O3/γ-Al2O3复合氧化物催化剂,考察了La2O3 的加入量、预处理方法对催化剂CO选择性氧化反应性能的影响,并通过XRD、H2-TPR、CO-TPR、XPS等手段对催化剂进行了表征。结果表明,添加La的 Ru1La6/Al2O3催化剂在110-170℃时具有99％以上的CO转化率,且催化剂的选择性在55.7%以上。和Ru/Al2O3相比,Ru1La6/Al2O3催化剂在较低温度下具有活性,活性温度区间变宽,适量La2O3的加入提高了钌物种的表面分散性,使催化剂表面活性位点增多,有利于CO的吸附和氧化,提高了催化剂的活性和选择性。和其他方法相比,经氢气预处理后的Ru1La6/Al2O3催化剂活性最佳,催化剂上Ru物种结合能降低,表面钌物种活性位增多,且表面晶格氧浓度增大,更有利于CO气体在催化剂表面上的氧化反应。     

Ru-La_2O_3/γ-Al_2O_3催化剂合成、表征及CO选择氧化

采用浸渍法制备系列Ru-La2O3/γ-Al2O3复合氧化物催化剂,通过XRD、H2-TPR、CO-TPR、XPS、BET等方法对催化剂进行表征,考察La2O3的加入量、预处理方法对催化剂上CO选择氧化性能的影响.结果表明,110-170℃时Ru1La6/Al2O3催化剂上CO转化率达到99%以上,氧气利用率达55.7%以上.和Ru/Al2O3相比,Ru1La6/Al2O3催化剂在较低温度具有高活性,活性温度区间变宽.适量La2O3的加入促进了活性组分在载体表面分散,提高了催化剂的活性.经氢气预处理的Ru1La6/Al2O3催化剂活性最佳,催化剂上Ru物种结合能降低,表面钌物种活性位增多,且表面晶格氧浓度增大,更有利于CO气体在催化剂表面上的氧化反应.     

硫化CoMo催化剂上H2同时还原NO和SO2的研究I．H2还原NO反应

研究了Al2O3担载的硫化CoMo催化剂上NO被H2还原的规律，并考察了不同Mo含量的CoMo/Al2O3催化剂、单一的Mo／Al2O3和Co/Al2O3催化剂，以及原料气中H2／NO比对反应活性和选择性的影响。结果表明，硫化的5．1％C-15．2％Mo/Al2O3催化剂具有最高的催化活性和选择性，在200℃以下时反应产物为N2O，在350℃以上时则完全转化为N2．进一步增加Mo含量引起在350－450℃间N2选择性轻微下降，提高原料气中的H2含量可明显提高反应活性和N2选择性，但当n（H2）／n（NO）＞3后反应性能不再变化。催化剂具有较高的稳定性，反应产物中始终未观察到有H2S或SO2产生，即反应未引起催化剂中的晶格S流失。这说明H2的存在抑制了NO对硫化物表面的氧化所导致的催化剂失活。     

CeO2改性的Pd/Al2O3催化剂在加氢脱硫反应中的抗硫性能

采用浸渍法制备CeO2改性的Pd/Al2O3催化剂,以噻吩加氢脱硫为探针反应,考察了Pd/Al2O3 和Pd-CeO2/Al2O3催化剂的活性和抗硫性能,并运用CO吸附、FT-IR、TG等分析测试技术研究表征了催化剂性质. 结果表明,Pd-CeO2/Al2O3催化剂比Pd /Al2O3催化剂具有较低的硫化度. 在连续反应中,Pd-CeO2/Al2O3催化剂的抗硫失活能力较强. CeO2的加入导致了Pd-S键能的减弱,在Pd-CeO2/Al2O3催化剂上H2S主要吸附在CeO2上而不是Pd原子上. Pd-CeO2/Al2O3抗硫能力的提高是由于Pd-Ce结合导致Pd缺电子状态,减少了Pd的硫化失活而引起. CeO2对H2S的竞争吸附造成与CeO2结合作用的Pd处于较低的H2S分压,减少了Pd失活的几率.     

硫化CoMo催化剂上H2同时还原NO和SO2的研究Ⅰ.H2还原NO反应

 研究了Al2O3担载的硫化CoMo催化剂上NO被H2还原的规律，并考察了不同Mo含量的CoMo／Al2O3催化剂、单一的Mo／Al2O3和Co／Al2O3催化剂，以及原料气中H2／NO比对反应活性和选择性的影响．结果表明，硫化的5．1％Co－15．2％Mo／Al2O3催化剂具有最高的催化活性和选择性，在200℃以下时反应产物为N2O，在350℃以上时则完全转化为N2．进一步增加Mo含量引起在350～450℃间N2选择性轻微下降．提高原料气中的H2含量可明显提高反应活性和N2选择性，但当n（H2）／n（NO）＞3后反应性能不再变化．催化剂具有较高的稳定性，反应产物中始终未观察到有H2S或SO2产生，即反应未引起催化剂中的晶格S流失．这说明H2的存在抑制了NO对硫化物表面的氧化所导致的催化剂失活．     

纳米金催化剂的抗水性能和抗硫中毒性能

与Au/Al2O3相比,复合载体负载的Au/FeOx/Al2O3具有更高的催化CO氧化的低温活性和稳定性,且表现出湿度增强效果,水分压为550~1 600 Pa时催化剂活性较高.在完全无水的环境中,催化剂发生快速不可逆失活;在饱和水汽的环境中,催化剂发生缓慢可逆失活.在水汽作用下的失活与纳米金粒子的粒径长大有关.助剂对催化剂抗水性能影响不大,但对抗硫中毒性能的影响较大.Au/CeO2/Al2O3催化剂显示有最佳的抗硫中毒性能.催化剂表面硫化物和硫酸盐的生成是导致催化剂不可逆硫中毒失活的主要原因.     

Raney-Ni-Mo/Al2O3催化剂的制备及其催化茚饱和加氢性能

以含钼为1.5%的镍-铝合金粉与拟薄水铝石按质量比为1∶1的比例,经成型、焙烧、浸取活化制备了负载型Raney-Ni-Mo/Al2O3加氢催化剂,通过XRD、BET、TG-DTA及SEM等手段对催化剂进行分析表征,并以茚加氢生成茚满的反应为探针,采用连续固定床加氢反应装置对所制备的催化剂加氢性能进行了评价.结果表明:成型合金A lloy-Ni-Mo/Al2O3的焙烧温度对于浸取活化后的Raney-Ni-Mo/Al2O3催化剂的抗压强度至关重要,比较适宜的焙烧温度为860℃,在该温度下合金中富铝相NiAl3向贫铝相Ni2Al3转变不仅有利于提高催化剂的加氢活性,而且金属铝被氧化生成α-Al2O3,使得制备的Raney-Ni-Mo/Al2O3加氢催化剂的强度能满足固定床装填要求.在反应压力2.0 MPa、温度180℃、WHSV=2 h-1、氢油比(V/V)为300∶1条件下,Raney-Ni-Mo/Al2O3催化剂催化茚加氢生成茚满的转化率在所考察的1 000 h周期内均高于90%,表明该催化剂具有较好的加氢活性及其活性稳定性.     

Synthesis of some derivatives of 3-amino-3-desoxyerythrose and 3-amino-3-desoxy-D-3-erythrose

The synthesis of derivatives of 3-amino-3-deoxy-L-erythrose by LAH or LAD reduction of the oxime of 1,2-O-isopropylidene α-L -glycero-tetros-3-ulofuranose is described.     

Synthesis of γγγ-trifluorocarbonyl compounds

γγγ-Trifluorocarbonyl compounds are easily obtained in a good yield by introduction of the 1,1,1-trifluoroethyl moiety (CF₃-CH₂-) on the -methylene group of a ketone.     

Vibrational spectra of CH3GeH3 and CD3GeH3

Infrared gas phase spectra of CH₃GeH₃ and CD₃GeH₃ have been investigated at a resolution of 0.06 cm⁻¹ and Raman spectra obtained in the liquid phase at low resolution. Several reassignments of the fundamental frequencies are proposed. Q-branch maxima from the five naturally occurring Ge isotopes have been resolved in several of the fundamental vibrations and new values obtained of rotational and Coriolis coupling constants for ν₇, ν₈, ν₁₀ and ν₁₂ of CH₃GeH₃ and ν₇, ν₈, ν₉, ν₁₀ and ν₁₂ of CD₃GeH₃. Germanium isotopic frequency shifts on ν_GeC are also reported.     

Freezing the polarization of CH3NH3PbI3 and CH3NH3PbI3-xClx perovskite films

Thin films of methylammonium lead halides, CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x, were deposited onto symmetrical microstructured electrode arrays of gold or platinum on Si/SiO₂ wafers. Polarization studies were carried out on perovskite films under vacuum in the dark. For poling, a constant voltage was applied to the samples while the temperature was cycled between 295 K and 4 K. The measured current densities depending on the temperature showed distinct characteristics relating strongly to the crystal phase and the dielectric properties of the perovskite films. Voltage sweeps were carried out at different scan rates at specific temperature intervals after poling. The polarization of the films due to the migration of iodide vacancies in direction of the blocking perovskite/metal interface was frozen almost up to room temperature. Charge carriers were only able to cross the blocking barrier and contribute to the current where the ions have accumulated during poling. All J-V curves showed hysteresis: inverted and regular hysteresis at room temperature and below, respectively. Inverted hysteresis originates from the slow accumulation of ions at the blocking barrier, while regular hysteresis arises from a distortion in the adjacent crystals which will be discussed.     

钙钛矿CH3NH3PbI3晶体的电化学

电化学方波伏安及循环伏安测量表明,钙钛矿CH₃NH₃PbI₃晶体在有机电解质中的氧化还原过程伴随着化学降解。该化学降解源于CH₃NH₃PbI₃晶体中铅离子的还原以及碘离子的氧化。通过电化学伏安法可以测定晶体的能带。     

Non-Isothermal Kinetics of the Decomposition Reaction of Cluster [Ag3WS3Br]（PPh3）3 and [Cu3WS3Br]（PPh3）3

The thermal behaviors of clusters [Ag3WS3Br](PPh3)3 and [Cu3WS3Br](PPh3)3 (PPh3=triphenyl phosphine) in a nitrogen atmosphere were studied under the non-isothermal conditions by simultaneous TG-DTG-DSC and EDS techniques. The results showed that the evolution of PPh3 generally proceeded before the release of the other moiety in one or two step-mode. The mechanisms, the kinetic and the thermodynamic parameters for decomposition of PPh3 of both clusters were determined and calculated by jointly using several methods, which showed that its evolution was controlled by Avrami-Erofeev equation. The results also showed that there was no new stable phase composed of W-Ag(Cu)-S-Br after release of organic moiety PPh3 and that CVD method was not applicable to their further processing.     

Addition of NH3 to Al3O3-

Recent computational studies on the addition of ammonia (NH3) to the Al3O3- cluster anion [A. Guevara-Garcia, A. Martinez, and J. V. Ortiz, J. Chem. Phys. 122, 214309 (2005)] have motivated experimental and additional computational studies, reported here. Al3O3- is observed to react with a single NH3 molecule to form the Al3O3NH3- ion in mass spectrometric studies. This is in contrast to similarly performed studies with water, in which the Al3O5H4- product was highly favored. However, the anion PE spectrum of the ammoniated species is very similar to that of Al3O4H2-. The adiabatic electron affinity of Al3O3NH3 is determined to be 2.35(5) eV. Based on comparison between the spectra and calculated electron affinities, it appears that NH3 adds dissociatively to Al3O3-, suggesting that the time for the Al3O3-NH3 complex to either overcome or tunnel through the barrier to proton transfer (which is higher for NH3 than for water) is short relative to the time for collisional cooling in the experiment.