Effect of citric acid on the synthesis of tungsten phosphide hydrotreating catalysts

The effect of using citric acid in the synthesis of unsupported tungsten phosphide (WP) hydrotreating catalyst was investigated by synthesizing WP using varying amounts of citric acid. Catalyst characterization was done using nitrogen physisorption, CO chemisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The activities of the catalysts were tested on a high pressure kinetics rig using the hydrodenitrogenation of pyridine as a test reaction. The use of citric acid in the preparation resulted in smaller WP particles—1–10 μm versus >100 μm when no citric acid was used. The characterization results suggest that the citric acid formed complexes with the W ions and limited the agglomeration of these ions during calcination. The smaller WP particles were more active catalysts for pyridine conversion on both per volume and per site basis.

The effect of using citric acid in the synthesis of unsupported tungsten phosphide (WP) hydrotreating catalysts was investigated by synthesizing WP using varying amounts of citric acid. The SEM images below show WP particles prepared without (left) and with a 1:4 W:citric acid ratio (right). Increasing the amount of citric acid present in the preparation significantly reduced the particle size, increased the surface area, pore volume and CO uptake. In addition, the smaller particles were more active for pyridine conversion at 320 °C and 1.72 MPa.Figure optionsDownload as PowerPoint slide