不可还原材料负载的纳米金催化剂:理性设计与优化

近年来,负载型金催化剂被视为多相催化工业化进程中的机遇和挑战,因而广受研究.载体的选取可以有效调控纳米金催化剂的化学结构及催化活性.针对载体本身对反应是否具有活性,可将其分为活性载体与惰性载体.活性载体主要为具有还原性的金属氧化物;而惰性载体,诸如碳基材料、氧化硅、氧化铝等,多为反应条件下不具备还原性或不可进行还原处理的材料,不释放活性氧物种,通常不具备显著催化活性.一般情况下,活性载体负载的金纳米粒子(Au NPs)在CO氧化反应、醇类选择性氧化反应、水煤气变换等多相催化反应中均展现出优越的催化活性及目标产物的选择性;而以传统不可还原性材料负载Au NPs时,若非采用特殊的优化手段,该类金催化剂的活性及稳定性通常差强人意.尽管如此,不可还原材料作为惰性载体,亦展现出无与伦比的独特优势,例如其多具有易于调控的表面性能、可调变的多样化微观结构,丰富的地壳储量和易于大规模产业化的优势等.因此,针对不可还原材料负载的纳米金催化剂,探讨创新性的改性手段及其对金催化剂活性与稳定性的理性调控,成为近年来纳米金催化领域中最引人关注的研究课题之一.然而到目前为止,基于惰性载体负载金催化剂的系统性总结工作仍未见报道.作者及其所在团队围绕Au-载体/助剂表界面性质的精准调控及理性验证,以CO氧化与醇类选择氧化等反应为探针,对基于不可还原材料的纳米金催化剂的设计理念和改性手段进行了多尺度的探索.基于本组研究工作及近十年相关文献报道,本综述将以几种典型的不可还原材料为例,针对负载型金催化剂的研究进展进行详尽的阐述.从催化剂设计的理论设想和实践方案入手,对特殊结构材料的独创性研制手段、二元金属掺杂及表面功能化手段、特殊氛围处理等备受关注的改性手段进行归纳.并进一步对改性手段影响表面化学结构、电子结构、Au-载体/助剂间的相互/协同作用、催化剂形貌的实例以及水物种参与对反应的影响等方面展开对比讨论.本综述旨在为致力于金催化研究工作及有志在该领域一展抱负的研究者拓展新的方向,全面诠释不可还原材料作为惰性载体在金催化领域的巨大应用前景,进一步激发不可还原载体负载金催化剂开发的新思路,推动纳米金催化的工业化进程.

Development of gold catalysts supported by unreducible materials:Design and promotions

Gold catalysis had been considered a highly efficient candidate for heterogeneous catalysis. It is well established that reducible-material-supported Au NPs are more reactive than the unreducible ma-terials, unless specific modifications are carried out. However, unreducible materials such as carbon materials, silica, and alumina have particular advantages, including the easily controlled surface property, adjustable microscopic structure, earth-abundant reserves, and facile industrial manu-facture. New strategies, influences, and mechanisms of modification to enhance the catalytic per-formance and thermal stability of unreducible-material-supported gold catalysts are among the most attractive research topics in gold catalysis. However, to the best of our knowledge, reports and reviews focused on unreducible-material-supported gold catalysts are lacking. Herein, the above concept will be thoroughly discussed regarding several typical unreducible supports, including the commonly used silica, alumina, carbon materials, and hydroxyapatite. The currently prevailing modification strategies will be summarized in detail from the aspects of theoretical conceptualiza-tion and practical methodology, including the ingenious synthesis method for catalyst with a specif-ic structure, the currently prosperous electrostatic adsorption, colloid immobilization, and the ap-plicative thermal gaseous treatment. The influences of physical and chemical modifications on the surface chemistry, electronic structure, interaction/synergy between Au-support/promoter, cata-lyst morphology and water precipitation will be also summarized. It is assumed that the review will shed light on significant studies on unreducible support in gold catalysis with the purpose of cata-lytic promotion and the promotion of the potential industrial demands in advance. Furthermore, the review will provide new insights into unreducible supports that can be potentially applied in gold catalysis.