2003 Progress Report: Synthesis, Characterization, and Catalytic Studies of Transition Metal Carbide Nanoparticles as Environmental Nanocatalysts

EPA Grant Number: R829624
Title: Synthesis, Characterization, and Catalytic Studies of Transition Metal Carbide Nanoparticles as Environmental Nanocatalysts
Investigators: Shah, S. Ismat , Chen, Jingguang G.
Institution: University of Delaware
EPA Project Officer: Hahn, Intaek
Project Period: March 1, 2002 through February 28, 2006 (Extended to February 28, 2007)
Project Period Covered by this Report: March 1, 2003 through February 28, 2004
Project Amount: $350,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text |  Recipients Lists
Research Category: Nanotechnology , Safer Chemicals

Objective:

The objective of this research project is to explore the possibility of using alternative catalytic materials, transition metal carbides, and oxycarbides (defined as oxygen-modified carbides) to replace platinum (Pt)-group metals for the reduction of NOx.

Progress Summary:

Result 1: Extended X-Ray Absorption Fine Structure (EXAFS) Studies of the Nanoparticles

EXAFS analysis shows the nearest neighbor coordination in materials. For our work, these studies are important because in light of result 1, WC (Tungsten Carbide) surfaces have catalytic behavior for NO decomposition similar to that of Pt. If we observe the same electronic structure and local chemistry in the WC nanoparticles as we do in the bulk, we can correlate their catalytic properties. Previously, we reported that the synthesis process can be modified to obtain desired surfaces. EXAFS is used to compare the local chemistry of the nanoparticles with that of bulk surfaces. Figure 1a shows the comparison of the W K-edge (the absorption edge of Tungsten) oscillation for the nanoparticle film, with spectra from the bulk and theory. Figure 1b shows the edge oscillations of the nanoparticles and the bulk only. The similarity of the structure is readily observable, indicating that the local chemistry of the nanoparticles is similar to that of the bulk, and therefore we should expect the catalytic properties of the nanoparticles to be similar to that of the bulk.
Figure 1. EXAFS Results Comparing the Nanoparticles, Bulk and Theoretical Spectra
Figure 1. EXAFS Results Comparing the Nanoparticles, Bulk and Theoretical Spectra

Result 2: NOx Decomposition With WCx Nanoparticles

Preliminary experiments to study NOx decomposition with WCx nanoparticles were conducted in an inline reactor. The reactor setup is shown in Fig. 2. The temperature of the reactor can be varied from room temperature to 1,000°C. Currently, we are using only a nitrogen column in the gas chromatographer (GC). This soon will be expanded to include a NO column. A mixture of 1 percent NO with He is used as the test gas. Flow rates are adjusted using mass flow controllers.

Figure. 2: In line reactor for NOx decomposition studies

Figure. 2: In line reactor for NOx decomposition studies.

A baseline for the experiment is obtained by passing the gas mixture through the reactor, without any catalyst. The baseline is shown in Fig. 3. With the addition of the catalyst, the direct decomposition of NOx occurs according to the reaction:

NOx ® N2 + O2

The N2 signal is detected by GC. Fig. 3 shows the increase in the N2 signal intensity as a function of the reactor temperature. The decomposition reaction starts to occur at temperatures above 200°C, increases rapidly up to about 500°C, and becomes constant beyond 500°C. We believe that the leveling off is a result of the loss of some carbon from the nanocatalyst. Our next set of experiments will include the addition of hydrocarbon to the feed gas. This not only will imitate the automobile exhaust better, but also will stabilize the carbon concentration in the nanoparticles and enhance the activity further with the increase in temperature
Figure 3. NOx Decomposition With and
Figure 3. NOx Decomposition With and
Without the Catalyst

Future Activities:

We will: (1) use reactive gas condensation with laser ablation for the synthesis of WCx nanoparticles, (2) study the addition of oxygen towards the stability of the WCx nanoparticles, (3) conduct de-NOx catalysis experiments with the addition of hydrocarbons to the feed gas, and (4) expand the catalysis studies to include the oxidation of hydrocarbon.


Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other project views: All 16 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Chen JG, Zhang MH, Rumaiz A, Shah SI. A comparative investigation of the self-hydrogenation and hydrogenation of cyclohexene. Catalysis (submitted, 2004). R829624 (2003)
not available
Journal Article Zhang MH, Hwu HH, Buelow MT, Chen JG, Ballinger TH, Andersen PJ, Mullins DR. Decomposition pathways of NO on carbide and oxycarbide-modified W(1 1 1) surfaces. Surface Science 2003;522(1-3):112-124. R829624 (2003)
R829624 (Final)
  • Abstract: Science Direct Abstract
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  • Supplemental Keywords:

    tungsten carbide, WC, environmental catalysts, reactive sputtering, reactive gas condensation, RGC, mobile sources, nitrogen oxides, acid rain, environmental chemistry, extended x-ray adsorption fine structure, EXAFS, nanoparticles, decomposition, gas chromatography, GC, catalyst, bulk and theoretical spectra,, RFA, Scientific Discipline, Air, Waste, Sustainable Industry/Business, air toxics, Remediation, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Civil/Environmental Engineering, Biochemistry, New/Innovative technologies, Chemistry and Materials Science, Environmental Engineering, Nitrogen dioxide, air pollutants, industrial wastewater, waste reduction, detoxification, in situ remediation, catalyst composition, automotive emissions, membranes, remediation technologies, nanotechnology, environmental sustainability, catalysts, reductive degradation of hazardous organics, catalytic studies, nanocatalysts, Nitric oxide, environmentally applicable nanoparticles, sustainability, nanoparticles, reductive dechlorination, hazardous organics, bimetallic particles, innovative technologies, pollution prevention, ultrafiltration, membrane-based nanostructured metals, membrane technology, recycle, reductive detoxification, transition metal carbides

    Relevant Websites:

    http://www.udel.edu Exit

    Progress and Final Reports:

    Original Abstract
  • 2002 Progress Report
  • 2004 Progress Report
  • 2005
  • Final Report