Iron molybdate synthesis using dicarboxylate decomposition methods for methanol partial oxidation to formaldehyde

The formation and subsequent decomposition of iron and molybdenum carboxylate precursors in a molten solvent made of the corresponding carboxylic acid was investigated for the purposes of iron molybdate catalyst production. These catalysts were tested for their ability to partially oxidise methanol to formaldehyde using gaseous oxygen. The use of oxalic acid was tested first and was found to be successful in production of iron molybdate forming highly active catalysts. These samples were found to be highly sensitive to Fe:Mo ratios with the best in terms of formaldehyde yield were 1:2.2 and 1:1.7 due to the superior mixing of iron and molybdenum on the surface and in the bulk content of the catalyst. Other Fe:Mo ratios tested caused non-homogeneous mixing of the iron and molybdenum resulting in lower formaldehyde yields overall. The oxalate method was found to be highly sensitive to water additions into the oxalate mixture with the formation of large quantities of COx selective Fe2O3 with small water additions, large additions caused a more coprecipitation approach to be observed. The use of malonic acid was tested and was found to outperform the oxalic acid examples. This was due to superior mixing of the iron and molybdenum causing a highly homogeneous composition. Similar Fe:Mo study found that a range of ratios(1:1.5, 1:1.9, 1:2.2 and 1:3.0) achieved very high formaldehyde yields. A calcination study showed that the malonate method was highly sensitive to changes in calcination conditions with both composition and performance altered dependent on conditions. Alterations of iron precursor using the malonate method found significant changes in catalyst composition depending on the anion used. Chloride and nitrate were found to be the best achieving very high yields. Acetate, oxalate, sulphate and phosphate were found to produce less homogeneous samples which negatively affected catalytic performance

The effect of sodium species on methanol synthesis and water-gas shift Cu/ZnO catalysts: utilising high purity zincian georgeite

The effect of sodium species on the physical and catalytic properties of Cu/ZnO catalysts derived from zincian georgeite has been investigated. Catalysts prepared with <100 ppm to 2.1 wt% Na+, using a supercritical CO2 antisolvent technique, were characterised and tested for the low temperature water–gas shift reaction and also CO2 hydrogenation to methanol. It was found that zincian georgeite catalyst precursor stability was dependent on the Na+ concentration, with the 2.1 wt% Na+-containing sample uncontrollably ageing to malachite and sodium zinc carbonate. Samples with lower Na+ contents (<100–2500 ppm) remained as the amorphous zincian georgeite phase, which on calcination and reduction resulted in similar CuO/Cu particle sizes and Cu surface areas. The aged 2.1 wt% Na+ containing sample, after calcination and reduction, was found to comprise of larger CuO crystallites and a lower Cu surface area. However, calcination of the high Na+ sample immediately after precipitation (before ageing) resulted in a comparable CuO/Cu particle size to the lower (<100–2500 ppm) Na+ containing samples, but with a lower Cu surface area, which indicates that Na+ species block Cu sites. Activity of the catalysts for the water–gas shift reaction and methanol yields in the methanol synthesis reaction correlated with Na+ content, suggesting that Na+ directly poisons the catalyst. In situ XRD analysis showed that the ZnO crystallite size and consequently Cu crystallite size increased dramatically in the presence of water in a syn-gas reaction mixture, showing that stabilisation of nanocrystalline ZnO is required. Sodium species have a moderate effect on ZnO and Cu crystallite growth rate, with lower Na+ content resulting in slightly reduced rates of growth under reaction conditions

The surface of iron molybdate catalysts used for the selective oxidation of methanol

The oxidation of methanol to formaldehyde is a major chemical process carried out catalytically and iron molybdate is one of the major catalysts for this process. In this paper we explore the nature of the active and selective surfaces of iron molybdate catalysts and show that the effective catalysts comprise molybdenum rich surfaces. We conclude that it is therefore important to maximise the surface area of these active catalysts and to this end we have studied catalysts made using a new physical grinding method with oxalic acid. For super-stoichiometric materials (Fe:Mo = 1:2.2) the reaction data show that physical mixing produces effective catalysts, possibly offering an improvement over the conventional co-precipitation method

Iron molybdate catalysts synthesised via dicarboxylate decomposition for the partial oxidation of methanol to formaldehyde

A series of iron molybdate catalysts were synthesised via a sol gel route using either oxalic acid or malonic acid. Catalysts synthesised using malonic acid were found to give improved formaldehyde yields over those prepared using oxalic acid or a standard coprecipitation method. This was attributed to the iron and molybdenum malonate precursors forming discrete ions that when precipitated gave a homogeneous distribution of iron and molybdenum in the final catalyst. Metal oxalate precursors and materials synthesised using coprecipitation gave less homogeneous structures containing iron rich centres that led to combustion of methanol to carbon oxides