NO adsorption and dissociation on Rh(111): PM-IRAS study
1Department of Chemistry, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA.
The Journal of Physical Chemistry. B
|March 24, 2006
Summary
Nitric oxide (NO) dissociation on Rh(111) occurs at lower temperatures than previously thought. New adsorption pathways involving atomic oxygen on Rh(111) surfaces were identified.
Area of Science:
- Surface Science
- Heterogeneous Catalysis
- Chemical Kinetics
Background:
- Understanding nitric oxide (NO) adsorption and dissociation on metal surfaces is crucial for catalysis and environmental applications.
- Previous studies on Rh(111) have provided insights but lacked conclusive details on surface structures and dissociation mechanisms.
- The role of surface intermediates and reaction pathways at varying pressures and temperatures requires further investigation.
Purpose of the Study:
- To investigate the adsorption and dissociation mechanisms of NO on Rh(111) using in situ spectroscopy.
- To clarify the surface structures formed during NO adsorption under different pressure and temperature conditions.
- To determine the onset temperature for NO dissociation on Rh(111) and identify influencing factors.
Main Methods:
- In situ polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) was employed.
- Experiments were conducted on a Rh(111) single crystal surface.
- NO gas was exposed at moderate (< or =10(-6) Torr) and high (1 Torr) pressures, with temperatures ranging from <275 K to 300 K.
Main Results:
- A transition from 3-fold hollow to atop bonding of NO was observed at moderate pressures (< or =10(-6) Torr) and temperatures (<275 K).
- This transition is attributed to gas-phase NO adsorption directed to atop sites by existing chemisorbed atomic oxygen (O) species in hollow sites, not NO migration.
- High pressure (1 Torr) NO exposure at 300 K exclusively resulted in atop NO, challenging previously proposed surface structures.
Conclusions:
- NO dissociation on Rh(111) occurs at significantly lower temperatures than previously reported.
- The presence of decomposition products, specifically atomic oxygen, influences NO adsorption pathways.
- Existing models for NO surface structures on Rh(111) at high pressures need revision based on these findings.
More Related Videos
Related Concept Videos
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
01:19IR Spectrum
When infrared (IR) radiation passes through a molecule, the bonds stretch or bend by absorbing the radiation. This absorption creates the molecule's absorption spectrum, which is the plot of its percentage transmittance versus wavenumber.
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete...
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete...
01:13Attenuated Total Reflectance (ATR) Infrared Spectroscopy: Overview
Attenuated total reflectance (ATR) infrared spectroscopy is a powerful analytical technique used to study the composition of materials. It is widely employed in chemistry, materials science, forensic science, and other fields where sample characterization is required. ATR has several advantages over traditional transmission IR spectroscopy, including the requirement of little to no sample preparation and the ability to analyze a wide range of samples.
The ATR process begins by directing a beam...
The ATR process begins by directing a beam...
00:55IR Spectrum Peak Intensity: Amount of IR-Active Bonds
When infrared radiation is passed through a molecule, absorption occurs if the molecule's vibration leads to a substantial change in its bond dipole moment. Transitions between vibrational energy levels, typically corresponding to infrared frequencies (4000–400 cm−1), allow absorption if the vibration significantly alters the dipole moment, making the molecule infrared active. The molecular bonds have different stretching and bending vibrations, resulting in various peaks with varying...