Identification of Subnanometric Ag Species, Their Interaction with Supports and Role in Catalytic CO Oxidation.
The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO₂, Ag/Mg/TiO₂ and Ag/Ce/TiO₂ catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals.
Departamento de Fisicoquímica de Nanomateriales, Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México (UNAM), Ensenada 22860, Mexico. Julia.Kotolevich@gmail.com.
Yulia
Y
Kotolevich
Department of Physical and Analytical Chemistry, Tomsk Polytechnic University, Tomsk 634050, Russia. ekaterina_kolobova@mail.ru.
Ekaterina
E
Kolobova
National Research Center "Kurchatov Institute", Moscow 123182, Russia. evxramov@gmail.com.
Evgeniy
E
Khramov
Departamento de Fisica Aplicada, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada 22860, Mexico. efren507.507@gmail.com.
Jesús Efren
JE
Cabrera Ortega
Departamento de Fisicoquímica de Nanomateriales, Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México (UNAM), Ensenada 22860, Mexico. mario@cnyn.unam.mx.
Mario H
MH
Farías
National Research Center "Kurchatov Institute", Moscow 123182, Russia. yzubav@googlemail.com.
Yan
Y
Zubavichus
Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México (UNAM), México, DF 04510, Mexico. rodolfo.zanella@ccadet.unam.mx.
Rodolfo
R
Zanella
Departamento de Fisicoquímica de Nanomateriales, Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México (UNAM), Ensenada 22860, Mexico. jmota@cnyn.unam.mx.|CONACYT Research Fellow at Centro de Nanociencias y Nanotecnología, UNAM, Ensenada 22860, Mexico. jmota@cnyn.unam.mx.
Josué D
JD
Mota-Morales
Department of Physical and Analytical Chemistry, Tomsk Polytechnic University, Tomsk 634050, Russia. pestryakov2005@yandex.ru.
Alexey
A
Pestryakov
Departamento de Fisicoquímica de Nanomateriales, Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México (UNAM), Ensenada 22860, Mexico. nina@cnyn.unam.mx.
Nina
N
Bogdanchikova
Institute of Catalysis and Petroleumchemistry (ICP), Spanish Council for Scientific Research (CSIC), Madrid 28049, Spain. vcortes@icp.csic.es.
Vicente
V
Cortés Corberán
D002248:Carbon Monoxide / Q000737:chemistry*; D002384:Catalysis; D046529:Microscopy, Electron, Transmission; D010084:Oxidation-Reduction; D010316:Particle Size; D012834:Silver / Q000737:chemistry*; D013499:Surface Properties
D012834:Silver; D002248:Carbon Monoxide
CO oxidation; interaction with support; sensitivity to pretreatments; silver catalysts; subnanometer species