(Preeti’Aghalayam,’Aug’2012)’ - · PDF filefast mixing, low pressure...
Transcript of (Preeti’Aghalayam,’Aug’2012)’ - · PDF filefast mixing, low pressure...
(Preeti Aghalayam, Aug 2012)
¡ Sir Humphrey Davy: 1817 – reaction of coal gas with oxygen on a glowing Pt wire
¡ Berzelius: 1836 -‐ Defined the term ‘catalysis’ ¡ Faraday: 1834 -‐ Proposed that reactants have to adsorb simultaneously at catalyst surfaces
(Catalysts were being used inadvertently, for making beer, wine, & cheese, in earlier times)
¡ Ostwald: 1900 – Catalysis, equilbria ¡ Haber: 1905 – Ammonia production catalyst ¡ Langmuir: 1920s – Surface chemistry ¡ Bosch: 1931 – High pressure reactor for ammonia
¡ Hinshelwood & Semenov: 1956 – Mechanisms of chemical reactions
¡ Ziegler & Natta: 1963 – Chemistry & technology of high polymers
4 G.A. Somorjai, K. McCrea / Applied Catalysis A: General 222 (2001) 3–18
Fig. 1. Timeline of the progress of heterogeneous catalysis.
the late 1960s/early 1970s, Boudart classified cata-lytic reactions into two groups: structure sensitive andstructure insensitive [5]. The structure sensitivereactions change their rate as a function of particlesize, while structure insensitive reactions remain at aconstant rate as the particle size increases [6]. Thisconcept has withstood the test of times. The conceptof bifunctional catalysis, by which to obtain a desiredproduct one needs two catalysts, was also developedin this period although it was proposed earlier by
Fig. 2. Turnover rates on Rh catalysts for reactions of CO with O2 and NO as a function of particle size exhibiting structure insensitivityand structure sensitivity of catalytic reactions [6].
Haensel. One catalyst produces a reaction intermedi-ate, which then diffuses onto the other catalyst wherethe reaction products form and desorb in the gas or so-lution phase. There are many examples of bifunctionalcatalysis. The selectivity changes due to pore size inzeolites have been shown to be due to the diffusionrate of molecules, which depends on the molecularsize and shape [7]. Using Linde 5A zeolite, Friletteet al. [7] showed that n-butanol could be dehydratedwith a conversion of 60wt.% while maintaining a low
Catalysis began by helping make bulk basic & inorganic chemicals, several centuries ago
It transitioned to a huge volumes and investments business with the advent of the oil economy and the need for petroleum re<ining
Further impetus was achieved via the petrochemicals industy
Soon, speciality chemicals production and enviromentally relevant catalysis became the exciting new trend
Today, in addition to being a mainstay in the chemicals industry, catalysts are expected to charter new directions for the world economy!
¡ 80 – 90% of current day products emerge from some or the other catalytic process
¡ As our focus shifts in the 21st century, the challenges, especially in petro industry, are remarkable
New materials: Catalytic membranes, hydrogen storage
Cheaper catalysts for pollution control
Biocatalysts for re<ining of petroleum
Fundamental studies: kinetics, characterisations
The petroleum economy especially can expect widespread changes
(from Marcilly, 2003)
(from Vlachos & Caratzolous,2010)
ARTICLE IN PRESS
up to two orders of magnitude higher than that of Li-basedbatteries (Vlachos, 2009).
The above applications underscore the need for developingsmall and efficient chemical plants. While smaller scales canstill be described with the core reaction engineering models,downscaling imposes new challenges that have been detailedelsewhere (Norton et al., 2005; Vlachos, 2009) and are onlybriefly mentioned here. Reactors need to be designed to ensurefast mixing, low pressure drop, high catalyst area for highconversions, and minimal transport (external and internal)resistances. In addition, catalyst requirements, such as activity,selectivity, safety (non-pyrophoric materials), and stability intransient operation, become more stringent. Integration of micro-units into compact, energy-efficient, self-sustained systems iscrucial given the lack of large heat and process integration withnearby plants.
4. Hydrogen economy, green hydrogen, and remote/offshoreutilization of natural gas
The concept of hydrogen economy has frequently been in therecent news and a DOE report has been published (Dresselhauset al., 2003; NRC, 2004). The ideal hydrogen cycle entails splittingof H2O to produce (green) hydrogen followed by its electro-chemical (green) combustion. The challenge, like CO2 utilization,is that H2O split is very hard to achieve at reasonable rates andefficiencies.
Hydrogen is the cleanest burning fuel. The much higherefficiency (compared with the current ICEs) and zero emissionsmake the PEM fuel cell running on H2 an appealing technology.Hydrogen addition to fossil fuels can stabilize combustion ofextra-lean mixtures (below their fuel lean flammability limit) inICEs, and thus, it could allow for reduction of temperatures andNOx emissions. Despite these obvious advantages, hydrogen is notavailable as a natural reserve, i.e., hydrogen is not an energysource but rather an energy carrier. It is currently produced andused in chemical industry for, among others, production ofammonia, methanol, and various refinery processes, such assulfur removal.
The strong opposition against a hydrogen economy from someof the scientific community arises in part from the fact that thereis no hydrogen surplus to realize a hydrogen economy and watersplit is too difficult to achieve. However, even if a hydrogeneconomy is never realized, increased hydrogen production fromalternative and renewable sources is still compelling sincehydrogen finds many industrial uses. For instance, the risingprices of crude oil and of natural gas have led to an increased priceof hydrogen. As a result, the price of diesel has increased over thatof gasoline due to more stringent regulations for sulfur removal.These problems can be mitigated if additional hydrogen produc-tion routes are developed.
The hydrogen economy consists of three legs: hydrogenproduction, storage, and use. The CRE community has tradition-ally been involved with the production of hydrogen (Figs. 2 and 3).Fuel cells (use) and catalytic storage/release offer newopportunities. The current production relies mainly on steamreforming of natural gas followed by two (high and lowtemperature) water gas shift (WGS) reactors. Depending on thepurity of hydrogen needed, a final stage of pressure swingadsorption or selective oxidation of CO or methanation may beneeded. This last process is deemed necessary in the case of PEMfuel cells to avoid poisoning of the Pt catalyst by COchemisorption. Coal gasification is another route for H2
production and is currently utilized to a less extent due to coalbeing the least clean fossil fuel. Given the huge coal reserves in the
US, it is expected that coal gasification to syngas and eventually tohydrogen or chemicals will gain substantial momentum in thenear future.
4.1. Green hydrogen production
The exploration of renewables for hydrogen production hasintroduced new processes to produce syngas. One such process isthe short contact time catalytic partial oxidation (CPOX) of liquid(oil) and solid lignocellulosic materials (e.g., wood chips) on Rh-based catalysts (Dauenhauer et al., 2006; Salge et al., 2006; Wanatet al., 2005). As elaborated further in the section on renewables, amajor advantage of this reforming technology is the minimizationor elimination of coke formation. An alternative to this reformingis the aqueous phase reforming (APR) of various oxygenatedmolecules to H2 (Cortright et al., 2002; Davda et al., 2005; Huberand Dumesic, 2006; Huber et al., 2003), e.g.,
C6HxO6(l)+6H2O(l)-6CO2(g)+(12+x)/2H2(g); x=12 or 14 (APR)
Under certain conditions (Davda and Dumesic, 2003), H2/CO2
mixtures (with fractions of CO as low as 100 ppm) are produceddue to the enhanced contribution of the water gas shift (WGS)reaction during low-temperature (!500 K) operation. The low COcontent makes purification of H2 from CO2 (with a membrane) forfuel cells very feasible but is disadvantageous for Fisher–Tropschsynthesis. The CO:H2 ratio can be tuned by changing the support(Chheda et al., 2007a).
Fuel
+ Air
Fuel
Steam
Pure H 2Combustor
Fuel + Air
Fuel
Steam
Pure H2
SR
WGSPSA, PROX, methanation
Fig. 2. Schematic of the flow sheet for syngas and H2 production.
Steam reforming CO
H2
CH 4
CO 2
H2O
CHO
H2OSteam reforming
Water-gas shift
H2O
CO
Water-gas shift
CO
H2
CO
H2
CO
H2
O2
O2
Partial o
xidation
Partial oxidation
CH 4
CO 2
H2O
CHO
Dry
ref
orm
ing
Dry reform
ing
CO2
CO2
CH4
CO2
H2OO2
O2
O2
O2
CHO
CH3O
CH2O
CH3OH
CHO
H2O
Combustion
Combustion
Oxidation
Oxidation
Fig. 3. Schematic of the reaction network in converting natural gas to syngas (seeFig. 2). In most of these reactions, more than one overall reactions happen. In CPOXand ATR, combustion, steam reforming, water gas shift, and direct formation ofsyngas are all possible depending on operating conditions and mass transferlimitations.
D.G. Vlachos, S. Caratzoulas / Chemical Engineering Science 65 (2010) 18–2920
The Hydrogen Economy has to rely heavily on catalysts
ARTICLE IN PRESS
This paper focuses mainly on select emerging technologies andprocesses where the CRE community can significantly contributein solving the energy problem, mainly through innovation inheterogeneous catalysis and reactors. Topics touched uponinclude process intensification (PI) and efficiency, hydrogeneconomy, offshore and remote natural gas utilization, andrenewables, such as biomass utilization and transformation ofvarious waste streams. As underscored herein, a crosscuttingtheme emerging for future power generation is processing atscales smaller than those of the conventional refinery andpetrochemical plants. Future research needs are finally outlined.
2. Improving process efficiency
While the quest for alternative and renewable energy sourceswill be very important in meeting the increasing energy needs, akey aspect in overcoming the energy and environmental chal-lenges is to improve process efficiency of existing and newprocesses (Nat.Acad.Press, 2008). This is particularly importantsince fossil fuels will continue to constitute the backbone of ourenergy supply.
Several processes exhibit low energy efficiency. For example,the overall efficiency in converting chemical energy, starting froma power plant running on coal, and ending with light is just 2%:62% of the initial energy is lost in the power plant, 2% intransmission lines, and 34% as heat in light lumps (Nat.Acad.Press,2008). As another example, the efficiency of a typical internalcombustion engine (ICE) is of the order of !20%. This low fractionis despite the progress made in fuel efficiency of automobiles from18 mpg (1978) to 27.5 mpg (1985) to an imposed average of35 mpg (2030) for all cars, SUVs, and light trucks (Nat.Acad.Press,2008), due mainly to improvements in light materials.
How do we improve process efficiency? Improved efficiencyusually entails catalyst and/or reactor/flow sheet optimization.Selectivity is, by and large, the single most important factor.Improved selectivity implies reduced waste and reduction orelimination downstream of the energy-intensive separation units.High throughput experiments and insights gained from computa-tional catalysis promise the development of more selectivecatalysts. An example is the epoxidation of ethylene to ethyleneoxide on Ag-based bimetallic and doped catalysts (Dellamorte etal., 2007) and many more are emerging. Catalyst design willunquestionably play a key role in both conventional processes andbiomass conversion.
Process intensification (PI) entails the enhancement of theeffective rate by increasing transport rates and/or impartingmultifunctionality into devices (Stankiewicz, 2007). The net resultcan be improvement of process efficiency, reduction in size (withan associated reduction in capital cost), and/or in operation cost.Several concepts for PI have been developed over the past fewyears. The overall idea of multifunctional reactors was madepopular about two decades ago (Agar and Ruppel, 1988; Wester-terp, 1992). A popular example of PI is reactive separation, withthe reactive distillation (Malone et al., 2003) of MTBE by EastmanChemicals being a successful commercial test bed. Membranereactors for equilibrium-limited reactions or for selectivelyremoving a product that inhibits catalysts is another example ofreactive separation (Harale et al., 2007). Reactive adsorption forCO2 capture during the water gas shift reaction is a recentlyexplored application (Dadwhal et al., 2008; Martavaltzi andLemonidou, 2008). Miniaturization of chemical processes leadsto enhanced transport rates and concomitant size reduction. Asdiscussed further below, this size reduction is deemed essentialfor smaller or distributed scale (remote, offshore, transportation,portable power) applications. Integration of heat exchangers with
reactors in making efficient, compact systems has also beenintensively studied (Kolios et al., 2005, 2007). The parallel-platecatalytic reactor (where an endothermic and an exothermicreaction take place on opposite sides of a wall that serves as aheat exchanger) is a fairly common configuration of spatialcoupling (Fig. 1). Heat recuperation strategies via recirculationor regeneration are essential strategies (Federici and Vlachos,2008; Jones et al., 1978; Lloyd and Weinberg, 1974; Matros andBunimovich, 1996; Neumann and Veser, 2005) for energy lossminimization. Additional examples of PI will be discussed below.
3. Distributed power generation and downscaling ofchemical processes
In a recent report, it was suggested that ‘building small plantsnear customers, known as distributed generation, may becomemore important in order to meet demand and maintain reliability’(Nat.Acad.Press, 2008). Processing at smaller scales can meetmultiple objectives, namely increased reliability, overcomingexpensive or impossible transportation from remote and offshorelocations, improved PI and enhanced efficiency, and the need forH2 production for PEM fuel cells for transportation and portabledevices.
Miniaturization will be central to several energy efforts in thefuture. As discussed below, if we were to realize a hydrogeneconomy in the short term, we would need onboard reforming.This will entail !108 reactors to runs all cars in the US alone. Inthe mid term, and assuming that suitable nanomaterials forhydrogen storage are developed, hydrogen may be produced ingas stations (!105 in the US) to take advantage of the liquid fueldistribution infrastructure. When compared with the operating149 refineries in the US, the aforementioned numbers indicatereduction in reactor volume and increase in the number ofreactors needed for H2-based transportation economy.
Remote and offshore utilization of natural gas will requiresmaller-scale systems (Lerou, 2006). One could envision futuresupertankers, being filled offshore with crude oil, to be smallchemical plants transforming natural gas into liquids via gas toliquids (GTL) or easy-to-liquefy gases, e.g., ammonia, which arethen transported to mainland. Achieving this goal will requiredownscaling the currently bulky steam reforming process. In thecase of biomass, feedstock utilization will be localized. This is dueto the large water content of biomass, which makes thetransportation cost high. It is anticipated that the optimal scaleplants (biorefineries) will be of the order of !1000 barrels perday, much smaller than the current refinery and petrochemicalplants.
Electronics (1–100 W) currently rely on batteries whoseefficiency is low and their weight is high (their mass energydensity is low). One could replace batteries with microchemicalsystems since the mass energy density of common liquid fuels is
catalyst
Fuel + O2 ! CO2 + H2O
CH4 + H2O ! CO+3H2
Wall
Fig. 1. Schematic of multifunctional catalytic parallel-plate microreactor. Catalyticcombustion occurs on a Pt washcoat catalyst in one channel and steam reformingof methane on a Rh washcoat catalyst in the other channel. The (thin) separatingwall serves as a compact and efficient heat exchanger.
D.G. Vlachos, S. Caratzoulas / Chemical Engineering Science 65 (2010) 18–29 19
Energy ef<icient processes will require new ideas-‐ such as this combined reactor/heat exchanger in micro-‐scale
The current challenge is to design catalysts to explore these new vistas
First implemented in the USA in 1975
In Japan & Europe in 1986
Currently, all over the world!
Challenges today: • Selectivity • Cold start emissions • Fuel-‐lean engine • Biofuel engines • CO2 & PM • Bi-‐functional catalysts
This catalyst can reduce NO in fuel-‐lean engines without problems of
NH3 slip
New age engines and new age ground rules have kept researchers on their toes! (from Schauer et al.,2012)
¡ Picture this: metallic gold is typically chemically inert. But prepared in a special way – depositing only particles that are a few nanometers in size – makes it a viable catalyst for several reactions!
settled, it appears that mild reduction treatments may be
preferred in many instances, even if those leave some ofthe organic matter behind [30]. In fact, it is possible that
the remaining carbonaceous deposits may actually help
with the performance of the catalyst, at least in the pro-motion of mild reactions such as olefin hydrogenations
[37]. Access to the metal inside dendritic or colloidal
structures may also be possible in liquid solutions [38], inwhich case the catalyst may not even require special acti-
vating treatments. The issue of the activation of heteroge-
neous catalysts prepared by these new self-assemblymethodologies requires further studies.
When considering nanoparticle size in heterogeneous
catalysts, one extreme is catalysis by one single atom, orperhaps by a small number of atoms in a well-defined
molecular cluster. The behavior of the catalyst in suchcases may resemble more closely that of homogeneous
catalysts, where selectivity can sometimes be controlled at
a molecular level. In fact, the heterogeneous catalysts canbe prepared by starting with the corresponding discrete
molecular clusters [39]. However, the interaction of the
atoms of the catalytic phase with the support is rarelynegligible, and needs to be considered. The final structure
of the surface species may also dynamically change as the
pretreatment or reaction conditions are changed, and thefinal active phase may exhibit very different characteristics
to those of the original organometallic precursors. An
interesting example of a change in the structure of thecatalyst leading to changes in reaction selectivity has been
recently reported for the conversion of ethylene on sup-
ported rhodium catalysts [40]. In that case, the initialRh(C2H4)2 complexes bonded to a crystalline zeolite HY
support could be made to remain isolated and to display
high selectivity for the dimerization of ethylene to butenesand butane under most conditions, except upon exposure to
highly reducing environments, after which they were seen
to form small metal clusters and to preferentially promotehydrogenation to ethane instead. Curiously, this transfor-
mation was shown to be reversible: the isolated-Rh
dimerization sites could be regenerated upon exposure ofthe catalyst to ethylene-rich mixtures. In general, the use of
small molecular clusters as precursors for the preparation
of heterogeneous catalyst could be quite useful if issues ofstability and selectivity can be worked out.
3 Nanoparticle Shape
Perhaps more interesting than controlling the performanceof catalysts by controlling the size of the nanoparticles of
the active phase is the idea of exerting that control via theselection of their shape. It has been long known that some
catalytic processes are structure sensitive, which in tradi-
tional catalysis has come to mean that their performance interms of activity or selectivity changes significantly with
the method used for their preparation. However, this
behavior has been justified on the basis of the associatedchanges in the distribution of particle size in the resulting
catalysts [41]. It has only been recently, with the incor-
poration of methods to better control particle size andshape independently of each other, that the effects of those
two parameters have started to be untangled.
In surface science studies using model system, structuresensitivity has traditionally been probed by comparing
chemical reactivity on single crystals exposing surfaces
with different orientations [5, 8]. Initial studies on chemi-sorption were later extended to catalytic rate measurements
using so-called ‘‘high pressure cells’’ [42–44]. Those
studies have been quite useful, but also revealed someintrinsic limitations, in particular the fact that they cannot
Fig. 2 Pyrrole hydrogenation selectivity at 413 K (4 torr pyrrole,400 torr H2, 2 % conversion) as a function of the size of the Ptnanoparticles, dispersed on a HY zeolite, used as catalysts [32].Hydrogenation to pyrrolidine is facile in all cases, but further
hydrogenolysis to n-butylamine can only be partially avoided if smallnanoparticles, of diameters on the order of *1 nm, are used. Figurecourtesy of Jeong Park and Gabor Somorjai, reproduced fromRef. [32] with permission. Copyright 2009 American Chemical Society
504 F. Zaera
123
We are now able to really control size of the catalyst particles we make (from Zaera,2012)
¡ How does Zeolite microporosity control reactivity? àby selectively allowing access to an active site within the zeolite cavity!
¡ para-‐xylene can gain access to the inside of the zeolite channel, whereas the meta-‐ and ortho-‐ forms of xylene are sterically hindered from doing so.
We are now able to really understand how these magical things work! (from Bill Vining’s work)
New experimental techniques help us with molecular level pictures! (from Somorjai & Wang 1997,)
Electron based microscopy
Molecule/ion based spectroscopy
Photo-‐mediated spectroscopy
Scanning tunneling microscopy
( )G.A. Somorjai, M.X. YangrJournal of Molecular Catalysis A: Chemical 115 1997 389–403 393
� .Pt 110 surface exposed to ambient pressures ofhydrogen, oxygen and carbon monoxide at 425K. Under 1.6 atm of hydrogen pressure, thesurface presents various sizes of missing-rowreconstruction. In 1 atm of oxygen, however,
� .enlarged 111 microfacets can be observed.The surface in 1 atom of carbon monoxideappears to have large scale terraces separated bymultiple height steps.The surface reconstruction is a reversible
process. The platinum surface was exposed todifferent gases alternatively and the surface
w xstructure changed accordingly 18 . In 1.6 atmH , chemisorbed oxygen reacts to form water2and desorbs from the surface. In CO environ-ment, the binding energy of hydrogen atoms onthe surface is reduced and surface hydrogens arereplaced by CO molecules. Under atmosphericoxygen pressure, surface CO molecules are oxi-dized to CO and the surface is switched to be2covered by oxygen. The conversion of surfacestructures is indicative of the adsorbate compo-sition change on the surface.
2.1.2. Coadsorption-induced reconstruction ofadsorbate oÕerlayerAdsorbate overlayer as well as substrate
atoms can be rearranged by adsorption of coad-sorbates. Surface species are highly mobile onthe surface. In many cases, adsorbate structuresare reorganized in order to accommodate othersurface species. A reconstruction of adsorbateoverlayers by coadsorption has been demon-strated in a STM and LEED study of sulfur
� . � .chemisorption on Re 0001 and Pt 111 sur-w xfaces 19 . Surface structures imaged by STM
are consistent with electron diffraction patternsobtained in complementary LEED studies. At a
�sulfur coverage of 0.25 monolayer one atom. � .per four substrate metal atoms , a 2=2 or-
dered sulfur structure can be observed, as shown� . � . � .in Fig. 4 a . On either Re 0001 and Pt 111
surfaces, coadsorption of carbon monoxidemolecules induces a reordering of sulfur struc-ture. The sulfur overlayer is compressed, creat-ing empty space on the surface for carbon
� . � .Fig. 4. STM images a before and b after the reordering of� . � .sulfur overlayer on Re 0001 induced by CO exposure. a The
� .round maxima are due to individual p 2=2 ordered sulfur atomsadsorbed at the hcp hollow site of the surface. Image size: 40=40˚ � . � .A. b A hole has formed in the p 2=2 layer where CO has
�adsorbed CO molecules are not visible in the STM images,.presumably due to their facile diffusion on the surface . The sulfur
atoms which resided previously in the hole have been compressedto form trimers of three atoms which appear as bright spots
˚surrounding the hole. Image size: 55=55 A.
monoxide adsorption. The new sulfur overlayer� .presents a 3 63= 363 R308 structure on
� . � � .. � .Re 0001 Fig. 4 b and a 63=63 R308 struc-� .ture on Pt 111 . The CO molecules have a high
mobility on the surface and are not visible inSTM experiments. The change of sulfur over-layer structure is reversible and the original� .2=2 sulfur structure can be restored afterdesorbing CO molecules at high temperature.Competitive adsorption and mobility of ad-
sorbates on the surface attribute to the coadsorp-tion-induced reconstruction of adsorbate over-layers. If surface species are immobile becauseof a high activation energy for surface diffusion,coadsorption cannot take place. On the other
( )G.A. Somorjai, M.X. YangrJournal of Molecular Catalysis A: Chemical 115 1997 389–403400
catalyst. An optimization of catalyst perfor-mance can be accomplished.UV light and X-ray radiation have also been
used in lithography studies. The main advantageof electron beam lithography over the othertechniques is its exceptional high resolution. Itcan generate features as small as a few nanome-
w xters 30 . Notice that the average particle size ofindustrial catalysts is 1–100 nm, electron beamlithography is, at present, the best choice inmodel catalyst preparation.
3.2. ReactiÕity tests
An initial reactivity test of metal clustersprepared by electron beam lithography has
w xyielded encouraging results 31 . A metal clustersample was prepared by Dr. S.J. Wind at IBMresearch center, Yorktown Heights. Platinumparticles of 50 nm diameter and 15 nm heightwith 200 nm periodicity have been prepared ona 0.5=0.8 cm oxidized silicon wafer. Scanning
� .electron microscopy SEM pictures of the metalcluster array are shown in Fig. 15.The cluster sample shows a remarkable sta-
bility upon annealing and exposure to ions andelectrons. It allows us to remove surface con-taminants by low energy ion sputtering andoxygen treatment. The sample can be character-ized by electron- and ion-scattering surface sci-ence spectroscopies. AFM studies indicate thatthe sample structure remains intact after surfacecleaning, catalytic reaction and sample charac-terization.The rate of ethylene hydrogenation over this
new model catalyst was measured in aUHVrhigh pressure system. The surface area ofmetal cluster arrays is one to two orders ofmagnitude smaller than a single crystal surfaceof comparable sample size. Fig. 16 shows theethane yield as a function of time at roomtemperature, along with a background signaltaken on a blank silicon wafer. The measuredturnover rate is in good agreement with previ-ous results obtained on conventional supportedcatalysts and single crystals. As shown in Fig.
Fig. 15. SEM micrographs of platinum cluster array fabricated byelectron beam lithography. The sample has a cluster size of 50 nmand a periodicity of 200 nm.
16, an increase of reaction rate is also observedupon increasing sample temperature.The saturation coverage of adsorbates on the
platinum cluster sample can be determined frompeak areas in thermal desorption studies. Thethermal desorption spectra of D and 13C18O2from the cluster sample are displayed in Fig. 17,along with reference spectra collected on a plat-inum foil. The ratio of deuterium desorbingfrom the cluster sample to that desorbing fromthe reference foil sample is 2–4 times greaterthan the same ratio for carbon monoxide. Thisindicates a spillover of deuterium from platinummetal clusters onto silicon oxide support, whichis a characteristic of dispersed metal catalysts.Through the collaboration with IBM, we have
accumulated valuable experience on electronbeam lithography, sample handling, surfacecleaning and reactivity studies of nanoscale
STM & SEM images of catalyst surfaces
¡ Catalysis is old science § Industrial catalysis is even older!
¡ Nevertheless, its contextually immensely relevant today in several walks of life
HOME ASSIGNMENT: Identify a modern day (alive as yet) scientist working in catalysis. Read some abstracts/summaries of their work. Bring me a name, affiliation, and 1-‐2 line descriptions of their research. Note down the source of your information. (We will read these out in class tomorrow)
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