Basic Investigation of Controlled Periodic Illumination Effects on Photocatalytic Reactions and Selectivity

摘要提案题目：受控周期性光照对光催化反应和选择性影响的基础研究提案号：cts -9903511首席研究员：Richard NobleInstitution: University of colorado半导体光催化是一种很有前景的环境应用方法。照明半导体已经成功地应用于环境修复中，修复了水溶液中的多种有机化合物和重金属。当TiO2被紫外光照射时，该室温过程催化氧化和还原反应。通过控制周期性光照（CPI）提高了这些反应的效率。本研究的目的是评估CPI在TiO2光催化中的应用，以提高化学生产的产率和选择性，并验证在氧还原反应中使用CPI时，氧吸附/电子转移是限速反应步骤的假设。研究了l -赖氨酸的光催化环化反应生成l -管道油酸。该机制被提出遵循两个途径：一个形成所需的l -异构体，另一个形成管道油酸的外消旋混合物。所提出的机制的第一步是由光产生的空穴选择性氧化其中一个氨基。CPI可能通过改变初始氧化或通过改变所提出的途径中其余步骤的相对速率来影响选择性。在氧气还原的第二系列实验中，将改变操作条件，以便确定氧气吸附和导带电子向被吸附氧的转移的影响。氧压和铂负荷的变化也将用于确定速率限制效应。

AbstractProposal Title: Basic Investigation of Controlled Periodic Illumination Effects on Photocatalytic Reactions and SelectivityProposal Number: CTS-9903511Principal Investigator: Richard NobleInstitution: University of ColoradoSemiconductor photocatalysis is a promising method for environmental applications. Illuminated semiconductors have been successfully used in environmental remediation for a wide range of organic compounds and heavy metals in aqueous solution. This ambient temperature process catalyzes oxidation and reduction reactions when TiO2 is illuminated with ultraviolet light. The efficiency of these reactions is improved through controlled periodic illumination (CPI). The goals of this study are to evaluate the use of CPI in TiO2 photocatalysis to improve yields and selectivity for chemical production and to test the hypothesis that oxygen sorption/electron transfer is the rate-limiting reaction step when using CPI in oxygen reduction reactions. The photocatalytic cyclization of L-lysine to form L-pipecolinic acid will be studied. The mechanism has been proposed to follow two pathways: one forming the desired L-isomer and the other forming a racemic mixture of pipecolinic acid. The initial step in the proposed mechanism is the selective oxidation of one of the amino groups by the photogenerated holes. CPI may affect the selectivity through changes in the initial oxidation or through changes in the relative rates of the remaining steps in the proposed pathways. In a second series of experiments with oxygen reduction, operating conditions will be changed so that effects of oxygen adsorption and transfer of the conduction band electron to the adsorbed oxygen can be determined. Changes in oxygen pressure and platinum loading will also be used to determine rate-limiting effects.