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.