Synthesis and crystal structure of a new heteronuclear complex of Fe(iii)–K designed to produce effective catalysts for CO hydrogenation

Abstract

A new paramagnetic heteronuclear complex formulated as [K₃Fe(μ-ox)₃(H₂O)₃]_n (1), where ox²⁻ is oxalate, has been synthesized under hydrothermal condition. The molecular structure of complex 1 was characterized by elemental analysis, Fourier-transform infrared spectroscopy (FT-IR) and single-crystal X-ray diffraction (SCXRD). The results of SC-XRD analysis revealed that complex 1 crystallizes in the centrosymmetric space group P2₁/c of a monoclinic system with cell dimension a = 7.7175 (4) Å, b = 19.8009 (7) Å, c = 10.2623 (5) Å, and β = 107.634 (5)° at 100 K. The thermal behavior of complex 1 was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The magnetic behavior of complex 1 was studied at room temperature by a vibration sample magnetometer (VSM). Thermal decomposition of the silica and alumina supports of complex 1 at 650 °C resulted in the main catalysts, Fe₂O₃-K₂O/SiO₂ and Fe₂O₃-K₂O/Al₂O₃. The catalytic activity of the main catalysts was evaluated for CO hydrogenation. For comparative purposes, the reference catalysts of Fe₂O₃-K₂O/SiO₂ and Fe₂O₃-K₂O/Al₂O₃ were prepared by the impregnation method. The structure and composition of the catalysts were investigated by FT-IR spectroscopy, powder X-ray diffraction (PXRD), N₂ adsorption–desorption analysis, scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive X-ray analysis (EDX). We tested all catalysts for hydrogenation of CO at 5 bar of pressure in the temperature range of 593–673 K. It was found that the main catalysts have better CO conversion and selectivity to desired products, such as light olefins, than the reference catalysts.