How do organic molecules interact with metal catalysts?

Michael SchmukerCynthia Luxford

Sponsor: Dr. Dalila Kovacs

Abstract

• The goal of these studies is to detect the interactions of organic molecules, such as alcohols, with metal catalysts. Understanding these interactions can provide insight into using green catalysts for chemically cracking biomass derived organic molecules as a source for energy and commodity chemicals.

These interactions can be studied via a number of different methods, such as FT-IR, ATR-IR, and NMR.

What did we do?

• Cyclohexanediols (CHD’s) are used as models of sugars.• The catalyst is reduced with H2 gas.• The CHD’s are dissolved in H2O.• Experiments are ran under variable pressure and temperature,

up to 220oC and 550 psi (37.5 atm).• Upon filtering solution from catalyst, the solution is analyzed via

GC/MS or HPLC.

Organic MoleculeCyclohexanediols

Metal Catalyst5% Pd on C

OH

OH

Pd106.42

46

The Problem

• Somewhere in the experiment, we lost mass.

H2O, Pd, C

OH

OH

OH

+ +

OH

OH

The total mass of products and reactants from Cynthia’s data for this reaction does not balance.

O

OH

Where could the lost mass be?

• The mass of CHD’s lost could have been cracked to organic molecules small enough to be in the gas phase at room temperature and pressure.

• If this is true, capturing the gas phase as it escaped the reactor for analysis is an option.

Is it on the catalyst?

• We know that H2 molecules become adsorbed on Pd surfaces.

• From literature* we know that alcohols can become adsorbed to other metals, such as Ruthenium, with the C-O bond parallel to the surface.

• From this knowledge, we decided to check the catalyst for our missing CHD’s.

*Barros, R; Garcia, A-R; Ilharco, L. J. Phys. Chem. B 2001, 105, 11186-11193.

How could we check the catalyst?

• FT-IR, ATR-IR, DRIFT-IR, 13C-NMR, and 1H-NMR were the best options.

• Each method of analysis offered different pros and cons.

• So far we have used FT-IR, 13C-NMR, and 1H-NMR.

FT-IRHow does it work?

• Infrared (IR) light is condensed and passed directly through the sample.

• The IR light causes bonds between atoms to stretch and bend.

• The change in the energy of the transmitted light is detected by the spectroscope and reported as transmission or absorbance.

O-H

C-O

C-H

ATR-IRHow does it work?

• ATR-IR reflects infrared light off of the surface of a sample and measures the angle of reflectance.

• ATR-IR can be used on aqueous phase samples or solids.

DRIFT-IRHow does it work?

• IR light is reflected off powder of the sample in the center of the unit. The scattered beams are then collected with mirrors and refocused onto the detector.

13C-NMR and 1H-NMRHow does it work?

• Nuclear magnetic resonance utilizes magnetic fields to affect atoms whose nuclei possess spin.

• Spin is caused by differing numbers of protons and neutrons in the nuclei of atoms.

• When the magnetic field becomes strong enough to flip the spin of the nuclei, a signal is detected.

What Did We Do?

• We attempted to dissolve the presumably adsorbed material from the catalyst in CDCl3.

• CDCl3 is a good organic solvent and is perfect for NMR.

• IR samples were prepared as KBr pellets. The catalyst was mixed with KBr and pressed at high pressure to make a thin, transparent film.

Nuclear Magnetic Resonance

• Traces of Pd in the NMR solution have paramagnetic effects, thus NMR is an unattractive option for analysis.

1 2 3

A B C D E

SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (4/12/05)

FT-IR• In many of our samples, water is the primary

molecule observed.• However, in one sample, C-O, and O-H

stretching are recognizable in our sample.

C-O

C-O O-H

O-H

C-H

C-H

CO2

Conclusions

• The FT-IR suggests that the starting alcohol is in fact still adsorbed to the surface of the metal.

• Recently, peaks for cis-1,2-cyclohexanediol and 2-hydroxy-cyclohexanone were identified in the HPLC of a solution obtained by triturating (wash) the catalyst. The HPLC analysis confirms the FT-IR results.

• ATRIR and DRIFT IR are the next methods of spectroscopic analysis.

The Future?

• The quality of the FT-IR spectrum necessitates use of ATR-IR and DRIFT-IR as possible alternative methods of analysis of the solid catalyst.

• Computational methods will be utilized to determine the thermodynamic stability of H2 and R-OH complexes with small Pd clusters.