Structural characterization of W-Ni-Al2O3 catalysts

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Nickel-aluminum oxide catalysts are widely used in various chemical processes.
• Tungsten is often added to modify catalyst properties, but its interaction with nickel in these systems requires further investigation.

Purpose of the Study:

• To synthesize and characterize W/Ni/Al2O3 catalysts.
• To investigate the effect of tungsten incorporation on the structural and chemical properties of Ni/Al2O3 catalysts.
• To understand the interaction between tungsten, nickel, and aluminum within the catalyst structure.

Main Methods:

• Catalyst preparation via coprecipitation of nickel and aluminum, followed by tungsten impregnation.
• Characterization using X-ray Diffraction (XRD) for phase identification.
• Surface analysis employing X-ray Photoelectron Spectroscopy (XPS).
• Advanced structural investigation using X-ray Absorption Spectroscopy (XAS), including X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS).

Main Results:

• XRD confirmed the presence of NiO and NiAl2O4 phases, with no distinct tungsten-containing phases detected.
• XPS revealed Al2O3, NiAl2O4, and aluminum tungstate (Al2(WO4)3) phases on the catalyst surfaces.
• XANES spectra were similar across all samples, indicating consistent electronic states.
• EXAFS analysis showed no direct bonding between tungsten and nickel atoms.
• The nickel coordination environment remained similar to the tungsten-free catalyst, with lower Ni-Ni coordination attributed to Ni-Al interactions.

Conclusions:

• Tungsten does not form direct bonds with nickel in these W/Ni/Al2O3 catalysts.
• The incorporation of tungsten does not significantly alter the local nickel coordination environment.
• Nickel-aluminum interactions play a crucial role in the observed structural properties of the catalysts.