Efficacy of zirconium hydroxide and cerium hydroxide for carbon dioxide adsorption and subsequent ethylene urea synthesis

Abstract

The elevating levels of atmospheric CO₂ present a dual challenge of environmental degradation and the underutilization of potential carbon resources. Addressing these issues, our study explores innovative adsorbent materials, Zirconium Hydroxide (Zr(OH)₄) and Cerium Hydroxide (Ce(OH)₄), synthesized via both co-precipitation and sol-gel methods, for their efficacy in CO₂ adsorption and conversion into ethylene urea (EU), a valuable chemical intermediate. Through meticulous characterization and comparative analysis, we discovered that sol-gel synthesized Zr(OH)₄ outperformed other synthesized adsorbents, displaying the highest pore volume (0.65 cm³/g) and average pore diameter (66.7 nm), indicative of internal hollow spaces and inter-particle pores, thereby enhancing porosity and CO₂ trapping efficiency. This material demonstrated a notable CO₂ adsorption capacity of 1.18 mmol/g, exceeding that of co-precipitated Zr(OH)₄ (0.92 mmol/g), co-precipitated Ce(OH)₄ (0.25 mmol/g), and sol-gel synthesized Ce(OH)₄ (0.45 mmol/g). Following CO₂ adsorption, Zr(OH)₄ and Ce(OH)₄ were utilized in a reaction with ethylene diamine (EDA) in a 2-propanol solvent, achieving successful synthesis of EU. Remarkably, at 160 °C, sol-gel derived Zr(OH)₄ produced the maximum yield of EU (0.23 mmol), surpassing co-precipitated Zr(OH)₄ (0.16 mmol), co-precipitated Ce(OH)₄ (0.12 mmol), and sol-gel Ce(OH)₄ (0.12 mmol). Our findings underscore the potential of employing Zr(OH)₄, particularly synthesized via the sol-gel method, as an efficient CO₂ adsorbent and accelerator in EU production. This research contributes to the field of CO₂ capture and utilization and opens avenues for developing cost-effective and environmentally friendly processes for synthesizing industrially relevant compounds.