Effect of Operating Temperature, Pressure and Potassium Loading on the Performance of Silica-Supported Cobalt Catalyst in CO2 Hydrogenation to Hydrocarbon Fuel

Iloy Iloy,Jalama Jalama

doi:10.3390/catal9100807

Abstract

Potassium (1–5 wt.%)-promoted and unpromoted Co/SiO2 catalysts were prepared by impregnation method and characterized by nitrogen physisorption, temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. They were evaluated for CO2 hydrogenation in a fixed bed reactor from 180 to 300 °C within a pressure range of 1–20 bar. The yield for hydrocarbon products other than methane (C2+) was found to increase with an increase in the operating temperature and went through a maximum of approximately 270 °C. It did not show any significant dependency on the operating pressure and decreased at potassium loadings beyond 1 wt.%. Potassium was found to enhance the catalyst ability to adsorb CO2, but limited the reduction of cobalt species during the activation process. The improved CO2 adsorption resulted in a decrease in surface H/C ratio, the latter of which enhanced the formation of C2+ hydrocarbons. The highest C2+ yield was obtained on the catalyst promoted with 1 wt.% of potassium and operated at an optimal temperature of 270 °C and a pressure of 1 bar.

Highlights

The promoting capabilities of alkali metals, namely potassium, have been investigated for a variety of catalysts and reactions, including steam reforming of bioethanol [1], water gas shift [2], N2 O decomposition [3], Fischer-Tropsch synthesis (FTS) [4,5,6] and CO2 hydrogenation [7,8,9,10,11]
The present study aims at systematically evaluating the promoting effect of potassium on a Co/SiO2 system used in CO2 hydrogenation under optimized temperature and pressure conditions
The addition of cobalt and potassium was done through co-impregnation with solutions of cobalt and potassium nitrates—both purchased from Sigma-Aldrich

Summary

Introduction

The promoting capabilities of alkali metals, namely potassium, have been investigated for a variety of catalysts and reactions, including steam reforming of bioethanol [1], water gas shift [2], N2 O decomposition [3], Fischer-Tropsch synthesis (FTS) [4,5,6] and CO2 hydrogenation [7,8,9,10,11]. One of the earliest studies on the use of potassium as a promoter for the catalyst used in CO2 hydrogenation to hydrocarbons is that of Russell and Miller [12]. They investigated several copper-activated cobalt catalysts at atmospheric pressure from 448 to 573 K with H2 /CO2 ratio varied from 2 to 3. Potassium was believed to selectively poison methane forming centres, and promote methylene radicals polymerization by the repression of the competitive hydrogenation reaction. Owen et al [13]

Objectives

Methods

Conclusion