The controlled catalytic oxidation of furfural to furoic acid using AuPd/MgIJ(OH)2

© 2017 The Royal Society of Chemistry. The emphasis of modern chemistry is to satisfy the needs of consumers by using methods that are sustainable and economical. Using a 1% AuPd/Mg(OH) 2 catalyst in the presence of NaOH and under specific reaction conditions furfural; a platform chemical formed from lignocellulosic biomass, can be selectively oxidised to furoic acid, and the catalyst displays promising reusability for this reaction. The mechanism of this conversion is complex with multiple competing pathways possible. The experimental conditions and AuPd metal ratio can be fine-tuned to provide enhanced control of the reaction selectivity. Activation energies were derived for the homogeneous Cannizzaro pathway and the catalytic oxidation of furfural using the initial rates methodology. This work highlights the potential of using a heterogeneous catalyst for the oxidation of furfural to furoic acid that has potential for commercial application

Understanding the Promotional Effect of Mn₂O₃ on Micro-/Mesoporous Hybrid Silica Nanocubic-Supported Pt Catalysts for the Low-Temperature Destruction of Methyl Ethyl Ketone: An Experimental and Theoretical Study

Pt_0.3Mn_<i>x</i>/SiO₂ nanocubic (nc) micro-/mesoporous composite catalysts with varied Mn contents were synthesized and tested for the oxidation of methyl ethyl ketone (MEK). Results show that MEK can be efficiently decomposed over synthesized Pt_0.3Mn_<i>x</i>/SiO₂-nc materials with a reaction rate and turnover frequency respectively higher than 12.7 mmol g_Pt^–1 s^–1 and 4.7 s^–1 at 100 °C. Among these materials, the Pt_0.3Mn₅/SiO₂-nc catalyst can completely oxidize MEK at just 163 °C under a high space velocity of 42600 mL g^–1 h^–1. The remarkable performance of these catalysts is attributed to a synergistic effect between the Pt nanoparticles and Mn₂O₃. NH₃-TPD and NH₃-FT-IR experiments revealed that exposed Mn₂O₃ (222) facets enhance the quantity of Brønsted acid sites in the catalyst, which are considered to be responsible for promoting the desorption of surface-adsorbed O₂ and CO₂. It is suggested that the desorption of these species liberates active sites for MEK molecules to adsorb and react. ¹⁸O₂ isotopic labeling experiments revealed that the presence of a Pt–O–Mn moiety weakens the Mn–O bonding interactions, which ultimately promotes the mobility of lattice oxygen in the Mn₂O₃ system. It was determined that the Mn⁴⁺/Mn³⁺ redox cycle in Mn₂O₃ allows for the donation of electrons to the Pt nanoparticles, enhancing the proportion of Pt⁰/Pt²⁺ and in turn increasing the activity and stability of catalyst. In situ DRIFTS, online FT-IR, and DFT studies revealed that acetone and acetaldehyde are the main intermediate species formed during the activation of MEK over the Pt_0.3Mn₅/SiO₂-nc catalyst. Both intermediates were found to partake in sequential reactions resulting in the formation of H₂O and CO₂ via formaldehyde

Investigating Catalytic Properties Which Influence Dehydration and Oxidative Dehydrogenation in Aerobic Glycerol Oxidation over Pt/TiO₂

The use of heterogeneous catalysts to convert glycerol into lactic acid has been extensively investigated in recent years. Several different strategies have been employed, but importantly, the highest production rates of lactic acid are achieved through aerobic oxidation under alkaline conditions. Despite the progress made in this area, insight into how the catalytic properties influence the selectivity of the competing pathways, oxidative dehydrogenation and dehydration, remains limited. Developing a deeper understanding is therefore critical, if process commercialization is to be realized. Using a model Pt/TiO2 catalyst, we set out to investigate how the supported metal particle size and support phase influenced the selectivity of these two pathways. Both these parameters have a profound effect on the reaction selectivity. Using a range of characterization techniques and through adopting a systematic approach to experimental design, important observations were made. Both pathways are first instigated through the oxidative dehydrogenation of glycerol, leading to the formation of glyceraldehyde or dihydroxyacetone. If these intermediates desorb, they rapidly undergo dehydration through a reaction with the homogeneous base in solution. Based on the experimental evidence we therefore propose that selectivity to lactic acid is influenced by surface residence time