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

控制周期照明的基础研究 对光催化反应和选择性的影响提案编号：CTS-9903511首席研究员：Richard Noble机构：科罗拉多大学半导体光催化是一种很有前途的环境应用方法。 发光半导体已成功地用于水溶液中各种有机化合物和重金属的环境修复。 当用紫外光照射TiO 2时，该环境温度过程催化氧化和还原反应。 这些反应的效率通过受控的周期性照射（CPI）来提高。 本研究的目的是评估使用CPI在TiO 2催化剂，以提高产量和选择性的化学生产和测试的假设，氧吸附/电子转移是限速反应步骤时，使用CPI在氧还原反应。 研究了L-赖氨酸光催化环化生成L-哌啶酸的反应。 已提出该机制遵循两个途径：一个形成所需的L-异构体，另一个形成哌啶酸的外消旋混合物。 在所提出的机制的第一步是选择性氧化的氨基基团之一的光生空穴。 CPI可能会影响选择性，通过在初始氧化的变化或通过在拟议的途径中的剩余步骤的相对速率的变化。 在第二系列的氧还原实验中，将改变操作条件，以便可以确定氧吸附和导带电子向吸附氧的转移的影响。 氧气压力和铂负载的变化也将用于确定限速效应。

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.