Mechanistic Analysis of Pd-based Auto exhaust Catalysts

• 85% of cars sold worldwide are fitted with catalytic converters. Without them, the average family car in the US would emit 15 tons of pollutants (carbon monoxide, hydrocarbons and nitrogen oxides), over a 10-year lifespan. Catalytic converters removes up to 98% of these pollutants.

• Precious group metals (Pd, Pt and Rh) are widely used as catalyst in catalytic converters. Addition of ceria shifts the

light-off to lower temperature and reduces cold-start emissions. It also helps to prevent sintering of palladium nano-particles at high temperature.

• Similar projects sponsored by NSF involves doping of Pd in pervoskitestructure. This enhances the mobility of Pd in-and-out of th pervoskite lattice, which increases activity for CO oxidation and reduces sintering.

sponsored by Catalytic Solutions, Inc.and National Science Fundation

Use of catalytic converters in automotive exhaust.

A) In-situ FTIR in transmission mode for mechanistic analysis.B) Light-off profiles for CO oxidation monitored by FTIR; effect of

ceria and steam in feed gas.

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B

Udayshankar Singh

Molecular Architecture using CH3ReO3 (MTO)

MTO behaves as a strong Lewis acid towards pyridine type bases and forms trigonal bipyramidal or octahedral Lewis base adduct depending on the type of donor bases. A metal complex can behave as a base towards MTO if it has dangling pyridine groups available for further coordination. The reaction of MTO with the dirhenium complex (Re2(µ-dppm)2Cl2(µ-C5H4NCOO)2) in CH2Cl2 forms either the adduct A or the molecular square B depending on the reaction stoichiometry. In the NMR of the adduct A the Re-methyl signal shifts high field (2.42 ppm) compare to the Re-methyl signal (2.65 ppm) of free MTO due to the binding of MTO-rhenium with nitrogen. The binding of two nitrogen atoms to the MTO-rhenium in the molecular square shifts the Re-methyl signal more high field (2.04 ppm).

N

N

C

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OO

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Re

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CO

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OO

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ReH3C

Re

O

O

O

Re

CH3

O

OO 2.04 ppmRe-CH3

2.42 ppmRe-CH3

Molecular structure of the MTO adduct (A) The molecular square (B)1H NMR of the adduct 1H NMR of the square

Ziegler-Natta Type Polymerization Catalysts

•Ziegler-Natta catalysts are typically prepared by impregnation of a Ti source on a MgCl2 support.

•The catalyst requires activation, which is commonly achieved by an organoaluminum complex, such as triethylaluminum or MAO.

•The choice of activator effects many properties of the system, including catalyst activity, thermal stability, and polymer properties. The aim of this project is to investigate the role of the activators in the catalyst system.

•Funding provided by the Dow Chemical Company.

High-density polyethylene beads

Scope of polyethylene uses. Böhm, L.L, Angew. Chem. Int. Ed., 77, 2003, 5010-5030.

Phillips Type Chromium Polymerization Catalysts

•Silica-supported chromium catalysts (Phillips catalysts) presently account for nearly one-half of the world’s HDPE production•Although these catalysts have been in use for over half a century, little is known in terms of the identities of their active sites and the mechanisms of their formation•Understanding the activation mechanism and being able to control the active site distribution will give the ability to vary the parameters that determine polymer properties•Well defined sites for characterization may be prepared by deposition of well-defined Cr precursors.•Characterization of active sites is performed by FTIR and X-ray absorption spectroscopy. Polymer is characterized by GPC, NMR, and IR techniques

Funding provided by theNational Science Foundation

Tris(allyl)chromium reacts on the surface of calcined silica to form an active catalyst for ethylene polymerization. (a) Silica activated at low temperatures forms high Mw HDPE. (b) Silica activated at high temperatures forms waxy oligomers. Ballard, D. G. H. Adv. Catal. 1973, 23, 263.

OCr

O O

OOCr

O O

Cl OH ∆ + HCl

OHCrO2Cl2 O + HCl

Cr

O O

Cl

Proposed route to formation of chromate sites on the silica surface without the need for aqueous precursors or high temperature calcination.

Catalytic properties of transition metal carbides

Heterogeneous catalysts can be formed by supporting (or grafting) a molecular species onto an oxide support. Silica is a widely used support for supported transition metal catalysts. We use compounds which give well-defined surface reactions leading to uniform materials.For example, grafting GaMe3 onto silica results in a 1:1 ratio of Ga per silanol≡SiOH + GaMe3 → ≡SiOGaMe2 + MeHSamples are taken to SSRL where intense X-rays are used to bombard samples. The element specific absorption of the X-rays produces a spectrum which can be modelled to gain information on the chemical environment and surrounding atoms of the absorber. The EXAFS of SiO2/GaMe3 material showed that the material is always dinuclear in gallium, previously established in the literature.

Figure: (left) Ga K-edge EXAFS of silica-supported GaMe3. Each grafting site is dinuclear in Ga; (right) A DFT model of dinuclear Ga site

Figure: (left) Stanford Synchroton Radiation Laboratory; (right) schematic of XAS setup

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Taha, Z. et al. Organometallics, 2006 in press.

X-ray Absorption Studies of Model Catalysts

Understanding the relationship between Surface Structure and Catalytic Properties in Heterogeneous Catalysts.

Understanding the First Interaction of Au(CHUnderstanding the First Interaction of Au(CH33))22(acac) with Silica(acac) with Silica

Although bulk gold is inactive as a catalyst, nano-sized gold particles and molecular organogold complexes are active, particularly when supported on metal oxides. However, the stability of the active forms of Au relative to bulk Au is often low. Relating the structures of gold catalysts to their activities and understanding their evolution under reaction conditions is key to slowing deactivation. We have studied the interaction of a volatile organogold precursor, Au(CH3)2(acac), with SiO2 by XAS, FTIR, and DFT calculations

The normalized Fourier transform magnitude of the EXAFS shows an intense peak at 1.65 Å, corresponding to atoms in the first coordination sphere directly bonded to Au, as well as several weaker peaks at higher R corresponding to non-bonded atoms in the second and higher coordination spheres. The latter are not evidence of Au-Au interactions, but are consistent with the acac ligand remaining coordinated to mononuclear Au.

The C-H frequencies increase with grafting due to H-bonding. The spectrum more closely resembles that of the molecular complex than that of the Hacac. These observations imply that the molecular complex stays intact as it is adsorbed on the support. After grafting the organogold complex, the IR intensity of the isolated hydroxyl stretching mode decreases, and a new band at 3447 cm-1 is observed. The peak is displaced from the hydrogen-bonded hydroxyl peak of unmodified silica, and is identified as a new hydrogen-bonding interaction between the organogold complex and the silica surface.

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Our group conducts both fundamental and applied research in surface chemistry and catalysis. The lab members are a combination of post doctoral researchers, engineering students, and chemistry students who work closely together to solve problems at the interface of chemistry and reaction engineering. Collaborations with researchers in the chemistry, chemical engineering, and materials department are ongoing. We frequently use: XRD, XPS, NMR, SEM, operando FTIR, BET, GC, GPC, GC-MS, UV-VIS, and DFT. XAS experiments are completed at the Stanford Synchrotron Research Laboratory, and operando quick-EXAFS spectra are collected at Argonne National Laboratory.

http://www.chemengr.ucsb.edu/~ceweb/faculty/scott/

•Transition Metal Carbides, such as molybdenum carbide, and tungsten carbide, are known to catalyze a variety of chemical reactions. These reactions include the water-gas shift reaction, methane reforming, and olefin metathesis.•We seek to properly characterize and test the catalytic activity of metal carbide nano-particles synthesized by our collaborators in the Materials Research Lab (Seshadri group).•Unsupported metal carbides powders are characterized using: BET, XRD, XPS, XANES, EXAFS, and SEM. •Catalysis is tested at various temperatures and flow rates in a gas flow reactor. Gas composition in and out of the reactor is monitors using FTIR, GC, and MS.

Funded by Department of Energy

Polyolefin Clay Nanocomposites

The addition of inorganic fillers to polyolefins is well established. Materials such as carbon black, talc, glass and clay are added to enhance the physical properties of the plastics. Further enhancement of the properties is possible if the filler size is decreased and the aspect ratio is increased, this is possible with clays as they have high aspect ratios and small sizes (~100 nm x ~1 nm).

In our lab we study clay/polyolefin composites using a variety of techniques including; GPC, NMR, XAFS, FT-IR, RAMAN, UV-Vis, XPS, TEM, XRD, DRIFTS, GC-MS, DMA, TGA and DSC.

Funding provided by Mitsubishi Chemical

300 ml Parr reactor used in lab to produce polyolefins.

Mercury Redox Reactions

We are studying redox reactions that lead to the reduction of mercury in coal-fired power plants. Most or the air-borne mercury emissions in the United States come from coal-fired power plants. The mechanisms by which mercury is reduced post-combustion in coal-fired power plants are not known. This hinders accurate simulations of mercury transport and deposition. Effects of various emissions reduction strategies are, therefore, difficult to predict. One of the goals of this project is to identify and quantify reactions of mercury in order to aid modelers in simulating and predicting the redox behavior of mercury.

Funded by Electrical PowerResearch Institute

Mercury transport in the environment

Formation of Hg(SO3)22- and reduction of Hg(II)

to Hg0 by S(IV)

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Back Row (Left to Right) : Eric Deguns, Dr.Juergen Eckert, Professor Susannah Scott, Dr. Udayshankar Singh, Sam Fleischman, Robert Savinelli, Dr. Swarup Chattopadhyay, Brian Peoples, Cori Demmelmaier, Miyako Hisamoto. Front Row : Tony Moses, Dr. Ziyad Taha*, Dr. Naseem Ramsahye*, Cathleen Yung, Heather Leifeste* (alumni status indicated by *). Not shown are: Brian Vicente, Andrew Seaward, and Justin Butler

Cori Demmelmaier

Eric Deguns

Robert Savinelli, Justin Butler

Cori Demmelmaier

Sam Fleischman

The red FTIR spectra is of the gases exiting the Mo2C plug flow reactor at low flow and a temperature of 350C. The black trace shows no conversion of CO to CO2 at r.t.

V--1

5% CO/ balN2

gas wettingtower

catalyst bed

IR beam

GC/MS gassampling port

thermocouples

Clam shellLindberg oven

thermocouple

heat rope,insulation

AC voltage control

flow meter

hygrometer

pressure gauge

pressure gauge

AC voltage control

hygrometer probechamber

AC voltage control

heat traced line

10 psi check valve

thermocouple

Water Chiller

1 psi check valve

H2N2v

v

PbO/Al2O3

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ich

eck

valv

e

Schematic drawing, (left), of water-gas shift catalyst testing station. (right) Dual plug flow reactor for Mo2C and WC catalyst beds. Gas comes in from the top and goes out the bottom.

H2O + CO H2 + CO2The water-gas shift reaction

makes H2 and removes CO, which is great for fuel cells.

CO2

CO H2OH2O

CO2

Abs

cm-1

Funded by Department of Energy

Funded by NOVA Chemicals

Funding provided by University of California

Brian Peoples, Cathleen Yung

Swarup Chattopadhyay, Tony Moses

Miyako Hisamoto