Colloidal Nanoparticles for Heterogeneous Catalysis

106 Pages·2019·7.575 MB·English

by  Priscila Destro

Springer Theses
Recognizing Outstanding Ph.D. Research
Priscila Destro
Colloidal
Nanoparticles for
Heterogeneous
Catalysis
Springer Theses
Recognizing Outstanding Ph.D. Research
Aims and Scope
The series “Springer Theses” brings together a selection of the very best Ph.D.
theses from around the world and across the physical sciences. Nominated and
endorsed by two recognized specialists, each published volume has been selected
foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield
of research. For greater accessibility to non-specialists, the published versions
includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor
explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill
provide a valuable resource both for newcomers to the research fields described,
and for other scientists seeking detailed background information on special
questions. Finally, it provides an accredited documentation of the valuable
contributions made by today’s younger generation of scientists.
Theses are accepted into the series by invited nomination only
and must fulfill all of the following criteria
(cid:129) They must be written in good English.
(cid:129) ThetopicshouldfallwithintheconfinesofChemistry,Physics,EarthSciences,
Engineeringandrelatedinterdisciplinary fields such asMaterials,Nanoscience,
Chemical Engineering, Complex Systems and Biophysics.
(cid:129) The work reported in the thesis must represent a significant scientific advance.
(cid:129) Ifthethesisincludespreviouslypublishedmaterial,permissiontoreproducethis
must be gained from the respective copyright holder.
(cid:129) They must have been examined and passed during the 12 months prior to
nomination.
(cid:129) Each thesis should include a foreword by the supervisor outlining the signifi-
cance of its content.
(cid:129) The theses should have a clearly defined structure including an introduction
accessible to scientists not expert in that particular field.
More information about this series at http://www.springer.com/series/8790
Priscila Destro
Colloidal Nanoparticles
for Heterogeneous Catalysis
Doctoral Thesis accepted by
the University of Campinas, Campinas, Brazil
123
Author Supervisor
Dr. Priscila Destro Prof. DanielaZanchet
Department ofChemical Engineering Institute of Chemistry
Federal University of São Carlos (UFSCar) University of Campinas
São Carlos, Brazil Campinas, Brazil
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-03549-5 ISBN978-3-030-03550-1 (eBook)
https://doi.org/10.1007/978-3-030-03550-1
LibraryofCongressControlNumber:2018960200
©SpringerNatureSwitzerlandAG2019
Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart
of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,
recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission
orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar
methodologynowknownorhereafterdeveloped.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom
therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse.
The publisher, the authors and the editors are safe to assume that the advice and information in this
book are believed to be true and accurate at the date of publication. Neither the publisher nor the
authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor
for any errors or omissions that may have been made. The publisher remains neutral with regard to
jurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations.
ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG
Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland
’
Supervisor s Foreword
Chemicalindustryisatthecoreofourlives,beingoneofthemaincontributorsfor
the significant improvement of the quality of life in the past centuries. However,
along with the technological development came the unbalanced use of the natural
resourcesthathasbeenshowninthepastdecadestobeunsustainable.Newactions
are required and within this context is the optimization of chemical processes and
development of more efficient and environmental-friendly alternatives needed.
Catalysisisoneofthemainpieces inthischallengepuzzle,andasignificantshare
of the world economy depends on the process that uses catalysts.
Despitesignificantadvancesinunderstandinghowcatalystswork,muchhasyet
to be overcome to achieve rational designing from first principles. In this long
pathway, the use of model systems has been proved to be a powerful tool. In this
thesis, the author explores the striking development of the synthesis of nanoma-
terials coupled to advances in in situ characterization tools at the atomic level to
address important aspects related to bimetallic catalysts. Catalysis is one of the
areas that has been benefited by the nanotechnology breakthroughs leading to a
deepunderstatingofseveralphenomenathattakeplaceatnanoscale.Infact,alarge
fraction of heterogeneous catalysts is formed by a highly dispersed metallic phase
onanoxidesupport.Thecatalystsare,therefore,nanostructuredmaterialsbynature
butspeciallycomplexduetothehugeimpactthatdifferentatomicsitesofthemetal
phase have in the catalytic performance, as well as the influence of the type of
support and metal–support interaction. In the case of bimetallic catalysts, the
combination of two metals increases the degree of freedom, allowing the modu-
lation and creation of unique catalytic sites.
Here, the author addresses important aspects related to bimetallic catalysts,
spanning from the synthesis of well-formed bimetallic nanoparticles by colloidal
methodstothepreparationofmodelcatalyststoaddressthecrucialroleofsupports
on the stabilization of the catalytic active phase. For that, the AuCu system was
chosenandappliedtoCOoxidation,animportantcatalyticreactionthatalsoworks
as a model reaction. An extensive analysis at the atomic level, exploring in situ
characterization tools is one of the highlights of this work leading to a deep
understanding of the formation mechanism of the AuCu alloy by the colloidal
v
vi Supervisor’sForeword
methodaswellasthemodificationofsupportedAuCunanoparticlesunderreaction
conditions.Inparticular,theauthorshowsthecrucialinfluenceofthesupportonthe
stability of the bimetallic phase and the formation of the active catalytic species
under reactions conditions.
This thesis is organized in three main chapters. The first one gives a brief
overviewoftheexcitingaspectsofnanomaterialsandbimetallicsystemspresenting
the AuCu system and CO oxidation reaction. The second one describes the efforts
to understand the mechanism of the AuCu alloy formation in organic medium and
the main parameters to tune the AuCu nanoparticles properties. The third chapter
describes the synthesis of model-supported catalysts based on the colloidal AuCu
nanoparticlesandhowthisstrategyallowedidentifyingtheimpactofsupportnature
onthestabilityoftheAuCualloyunderreactionconditionsandtheformationofthe
activecatalyticsites.Itisaneasytofollowbook,whichgivesaniceoverviewofa
multi-technique approach to tackle a challenging issue.
In Chap. 1, the author briefly introduces the colloidal method as a successful
approach to obtain nanoparticles dispersed in organic solvents and the rich variety
of particles that can be achieved by introducing a second metal. The gold–copper
alloysystemisdiscussedindetailanditisagoodreferencetostudentsinterestedto
understand structural and electronic aspects of bimetallic systems. The main chal-
lenges in heterogeneous catalysis and how the colloidal method approach can lead
to model catalytic bimetallic systems is addressed. It ends reviewing the use of
bimetallic catalyst in CO oxidation catalytic reaction.
Chapter 2 gives a overview of the challenges involved in understanding the
formationofbimetallicnanoparticlesbycolloidalmethodandthewaytoapproach
thisproblem.Thefirstpartaddressestheimpactofsynthesisparametersinthefinal
compositionoftheAuCusystemanditdemonstratesanelegantwaytocontrolthe
Au:Cu ratio by the final temperature. Using a combination of conventional tech-
niques, accessible to most chemical laboratories, the author shows the comple-
mentary information obtained by different techniques, in particular, how the
comparison of detail elemental analysis and X-ray diffraction of aliquots took at
different stages of the synthesis helped to identify an amorphous CuO -rich phase
x
that plays an important role in the AuCu nanoparticle formation through a
digestive-like ripping process. In the final part, an elegant experiment using
state-of-the-art techniques such as in situ X-ray absorption spectroscopy couple to
home-madesynthesisreactorconfirmstheinitialformationofAunanoparticlesand
thepresenceofCuO speciesthatevolvestotheformationofAuCunanoparticlesat
x
higher temperatures. This chapter gives a nice example of a multi-technique
approach to address the formation of alloys at nanoscale.
Chapter 3 presents the strategy to produce model catalysts from the pre-made
AuCunanoparticles,toaddresstherolesofAu:Curatioandthesupportinteraction
in the catalytic performance in CO oxidation. The author shows the impact of
differentpretreatments(oxidativeandreductive)intheperformanceofthecatalysts
and how the active catalytic species are stabilized under reaction conditions.
Severalinterestingaspectswereaddressedindetail.Forexample,theresiduesfrom
the colloidal synthesis (Cl species) that remained on the surface of the AuCu
Supervisor’sForeword vii
nanoparticles after deposition on silica could be easily removed by a reductive
pretreatment,leadingtoaverystableandactivecatalyst.Moreimportant,although
the pretreatments significantly affect the alloy, once the residues were eliminated,
the final active phase was dictated by the catalytic reaction. Moreover, the author
showsthatinertsupportsforthisreaction,suchasaluminaandsilica,infacthavea
significantimpactinthestabilizationoftheactivecatalyticspecies.Thecombining
of advanced in situ techniques was again the great differential of this part of the
workallowingunveilingthecrucialroleofthesupportinthecatalystsperformance.
Finally, the author presents her personal view of the main advances that was
achieved by her work. I believe that this work showed the relevance of combining
model systems with a multi-technique approach using advanced in situ character-
ization tools to address the challenges involving bimetallic catalytic systems. This
work gives an excellent overview of this elegant approach that should inspire
students working in materials science and heterogeneous catalysis.
Campinas, Brazil Prof. Daniela Zanchet
August 2018
Abstract
Thedevelopmentofnewmaterialsbydifferentstrategiesthatallowsthefinecontrol
of their properties is a field of extreme relevance in the current scientific scenario,
sinceithasadirectimpactonthedevelopmentofnewtechnologiesandnewenergy
sources. In this context, catalysis is directly influenced by these advances.
Inthiswork,itwaspossibletopresentthegreatpotentialofthedevelopmentof
new catalysts using the colloidal approach that allows the adjustment of the
essential properties of catalysts such as size, composition, and shape, to obtain
homogeneous and well-dispersed nanoparticles distributed in the catalyst surface.
In Chap. 2 the Au1−xCux alloy formation steps were evaluated, especially fig-
uringouttheeffectoftemperatureonparticlesizeandcomposition.Afundamental
part of this study was the real-time evaluation of nanoparticles formation using
X-ray absorption, where it was possible to identify critical phases in alloy forma-
tion,suchastheinitial formationofgoldnanoparticles insolution followed bythe
formation of an intermediate phase of Cu O, which is continuously digested and
2
incorporated into the preformed gold nanoparticles via solid-state digestion. These
observations point out ways to use the colloidal strategy for the synthesis of con-
trolled nanoparticles of other bimetallic systems, where size and composition are
key aspects for their applications.
In Chap. 3 was presented the application of the preformed Au1−xCux nanopar-
ticles to the heterogeneous catalysis. The particles were incorporated into different
supports which, although known in the literature as inert supports, can directly
influence the catalytic performance of the material. It has been observed that,
dependingonthesupportused,theprocessofalloying/dealloyingofthesupported
metal alloy is directly influenced and therefore, it generates distinct interface sites
that are responsible for its catalytic activity.
It is worth emphasizing two fundamental points in this work: (A) The investi-
gations performed were only possible thanks to a robust and sensitive system for
this type of transformations, and the colloidal synthesis fulfilled perfectly these
requirements. (B) The use of in situ techniques. In situ X-ray diffraction and
absorption measurements enabledthe evaluationof theactive phase of thecatalyst
ix
x Abstract
in real time, under different reaction conditions, providing faithful and relevant
information about the evaluated system.
In view of the obtained results, it is confirmed the importance of the develop-
ment of nanomaterial synthesis techniques and also of characterization, strategies
that directly influence the development of more effective catalysts and also of new
materialswhere interfaces areimportant,extendingtheapplicationofthese studies
not only to heterogeneous catalysis, but to the sciences of materials in general.