非水溶剂溶胶-凝胶法制备的纳米卤氧化镧在甲烷氧化偶联反应中的应用

采用非水溶剂溶胶-凝胶法制备了具有四方晶体相结构的纳米LaOX(X=Cl,Br).X射线粉末衍射和扫描电子显微镜结果表明,纳米LaOX样品的形貌规整、粒径均匀(平均粒径约为47nm).在甲烷氧化偶联(OCM)反应中,纳米LaOX显示出比常规尺度LaOX更高的催化活性和C2选择性,且纳米LaOX具有良好的稳定性.此外,常规尺度下,LaOBr催化剂活性和C2选择性高于LaOCl;纳米尺度下,两催化剂活性相差不大,但LaOBr上C2选择性明显更高

Ni的化学态对甲烷部分氧化反应机理的影响:能学分析

采用键指数归一-平方势(UBI-QEP)法对不同化学态Ni上甲烷部分氧化反应中各可能基元步骤进行了能学计算研究.结果表明,反应的速度控制步骤与金属Ni的化学态有关.还原态Ni上CO形成的反应速度控制步骤为表面上CH_3与O物种间的缔合,而带部分正电荷的Ni上CO形成的反应速度控制步骤则为甲烷氧助解离形成表面CH_xO物种.还原态和带部分正电荷的Ni中心在表面上共存时,反应的速度控制步骤将取决于表面CH_3形成与表面CH_3、O物种缔合两反应间的竞争,其竞争的强弱涉及Ni的化学态.此外,反应活性中心向正电荷的Ni转化时,会导致表面C和O及H和H物种缔合的活化能显著降低,有利于CO、H_2的形成,而表面CH_x物种解离则变得不容易,表面积炭受到明显的抑制

Nano-lanthanum Oxyhalide Prepared by Nonaqueous Sol-Gel for Oxidative Coupling of Methane

LaOX (X = Cl, Br) nanoparticles with tetragonal crystal structure were successfully prepared via sol-gel approach with non-aqueous solvents. Characterizations by X-ray powder diffraction and scanning electronic microscopy show that the LaOX nanoparticles are regularly in shape and highly uniform in size with an average diameter of about 47 nm. For oxidative coupling of methane (OCM), the nanosize LaOX catalysts have higher methane conversion and C(2) selectivity than the LaOX catalysts with conventional size and show good stability in activity and selectivity during the catalyst life test at 650 degrees C. At conventional size, the methane conversion and C(2) selectivity for OCM over the LaOBr catalyst are higher than that over the LaOCl catalyst, and at nanosize, there is not so much difference in methane conversion between LaOBr and LaOCl. However, the C(2) selectivity for OCM reaction over LaoBr is significantly higher than that over LaOCl, especially at low temperature.National Basic Research Program of China (973 Program)[2010CB732303]; National Natural Science Foundation of China[21033006, 20923004, 20373054

Influence of Ni Chemical States on the Partial Oxidation Mechanism of Methane: An Energetics Analysis

An energetics analysis of the possible elementary steps involved in the partial oxidation of methane (POM) over different chemical states of Ni was carried out using the unity bond index-quadratic exponential potential (UBI-QEP) method. The results show that the rate determining step for the partial oxidation mechanism of methane is related to the chemical state of the Ni. Over reduced Ni the rate determining step for CO formation is the association of surface CH(3) species with surface O species. Over a partial positive charged Ni surface the rate determining step is that methane dissociates into the CH(x)O species with the assistance of oxygen. Over the reduced and partial positive charged Ni sites in coexistence, however, the rate determining step depends on the competition between the formation of surface CH(3) species and the recombination of surface CH(3) species with surface O species. This competition is related to the chemical states of the Ni sites. If the partial positive charged Ni sites are predominant on the surface, the recombination of surface C species with surface O species and the recombination of surface H atom species favor CO and H(2) formation because of decreasing barriers. The surface CH(x) species does not dissociate easily and surface carbon deposition is significantly inhibited.National Natural Science Foundation of China[21033006, 20923004]; Natural Science Foundation of Fujian Province, China[2007J0168]; National Key Basic Research Program of China (973)[2010CB732303

一种基于MD5校验的电光混合加密方法

针对下一代无源光网络安全性不足的问题，文章提出了一种基于MD5信息摘要算法校验的电光混合加密方案。方案中采用Baker置乱算法和256 bit高级加密标准（AES）加密算法对图片数据进行加密，并结合低密度奇偶校验码（LDPC）纠错和MD5校验对加密图片数据进行纠错编码以及一致性校验。为进一步保证密钥和MD5摘要分发的安全性，方案中还采用超结构光纤布拉格光栅（SSFBG）对两者进行编码，使两者隐匿在系统噪声以下。仿真结果表明，经过SSFBG编码后，编码信号功率低至-50 dBm，可以达到数据在光纤信道上隐匿传输的效果。并且由于方案中加入了对接收数据的MD5校验，使得因恶意接入攻击造成的信息改变无法进行AES解码，在提升安全性的同时又节约了中央处理器（CPU）资源。最后，误码率曲线分析结果表明，加入LDPC纠错后，接收机灵敏度得到有效降低