Venkata D.B.C. Dasireddy

Effect of Various Au/Al2O3 Preparations on Catalytic Behaviour during the Continuous Flow Hydrogenation of an Octanal/Octene Mixture

Supported gold catalysts were prepared on a γ‐Al2O3 support by using the incipient wet impregnation and the deposition–precipitation methods. These catalysts were assessed for the continuous flow, liquid phase hydrogenation of an octanal/octene mixture, and their activity was compared with the activity of a commercially available Au/Al2O3 catalyst. These catalysts were characterised by inductively coupled plasma optical emission spectroscopy, hydrogen chemisorption, BET surface area and pore volume measurements, Raman spectroscopy, temperature‐programmed reduction of hydrogen, energy‐dispersive X‐ray spectroscopy mapping, HRTEM and powder XRD to determine gold crystallites. The results obtained revealed that gold crystallite size, dispersion and the presence of gold chloride had a significant effect on the product selectivity obtained. Large gold crystallites (particle size >15 nm) unevenly distributed on the alumina support obtained by using the wet impregnation method were inactive in hydrogenation. Hydrogen spillover resulted in the formation of protonic acid sites originating from molecular hydrogen, together with the formation of HCl‐catalysed acetal, and yielded 90 mol % selectivity towards the C24 acetal. In contrast, small gold crystallites (particle size <10 nm) evenly distributed on the alumina support obtained by using the deposition–precipitation preparation method facilitated the hydrogenation of the aldehyde and yielded 75 mol % selectivity towards the desired product, octanol.

Kinetics and Mechanism of the Oxidation of Coomassie Brilliant Blue-R Dye by Hypochlorite and Role of Acid Therein

The kinetics of the oxidation of a triphenylmethane dye, Brilliant Blue-R (BB – Na + ), in aqueous solution by hypochlorite as a function of pH was investigated. While the degradation of dye obeyed pseudo-first-order kinetics, the oxidation of the dye occurred through two competitive reactions facilitated by [OCl – ] and [HOCl]. Both reactions exhibited first-order dependence on [OCl – ] and [HOCl], respectively, but the hypochlorous acid initiated reaction was about ten times faster. The relative importance of the two paths rested on the pH-dependent concentrations of hypochlorite and hypochlorous acid. The overall second-order rate constants for the OCl – and HOCl initiated reactions are 1.2 ± 0.2 M –1 s –1 and 22.2 ± 1.2 M –1 s –1 , respectively. The reaction energy parameters were determined as E a = 35.5 kJ mol –1 , DH ‡ = 33.1 kJ mol –1 and DS ‡ = –191.9 J K –1 mol –1 for the OCl – driven oxidation; and E a = 26.8 kJ mol –1 , DH ‡ = 29.3 kJ mol –1 and DS ‡ = –204.6 J K –1 mol –1 for the HOCl facilitated reaction. The governing rate law and probable reaction mechanism were elucidated and validated by simulation. The three main oxidation products were 4-(4-ethoxyphenylamino)benzoic acid, 3-[(ethyl-hydroxyamino)methyl]benzene sulfonic acid and 6’-chloro-5’-hydroxybicyclohexylidene-2,5,2’-triene-4,4’-dione.

Effects of Organic Modifiers on a Palladium Catalyst in the Competitive Hydrogenation of 1‐Octene Versus Octanal: An Evaluation of Solid Catalysts with an Ionic Liquid Layer

The competitive hydrogenation between 1‐octene and octanal has been investigated with a ≈5 % palladium on alumina catalyst prepared in situ with the following organic modifiers: pyridine, 1‐methylimidazole, 1,3‐dimethylimidazole methylsulfate, 1,3‐dimethylimidazole bis(trifluoromethylsulfonyl)imide and methyltri‐sec‐butylphosphonium methylsulfate. The results of these investigations indicate that the ionic liquid modifiers have significant and specific effects on catalytic performance, for example, certain systems can completely suppress octanal conversion. In addition, analytical techniques reveal that the matrix and quantity of organic species on the used catalysts are different if different ionic liquids are used as modifiers. Surface studies also reveal that the modifiers have a noticeable effect on the crystallite size and chemisorption properties of the catalysts.

An investigation of Cu–Re–ZnO catalysts for the hydrogenolysis of glycerol under continuous flow conditions

Cu and Re monometallic and bimetallic catalysts supported on ZnO were synthesized via wet impregnation. The catalysts were characterized using XRD, TPR, Pulse TPD, TEM, SEM, XPS and BET surface area. TPR results showed that the presence of rhenium increases the reduction temperature of the catalysts and TPD showed that the presence of copper decreases the Bronsted acidity of the catalysts. SEM showed an improved distribution of metal oxide on the support after the incorporation of rhenium. These catalysts were evaluated in the hydrogenolysis of glycerol in a continuous flow fixed bed reactor in a temperature range of 150–250 °C and a H2 pressure of 60 bar. All catalysts were active, with activity being higher over the rhenium containing catalysts. At the lowest temperature (150 °C), 1,2-propanediol had the highest selectivity which decreased with increase in temperature. Subsequently, the selectivity to lower alcohols, such as methanol, ethanol and 1-propanol, and ethylene glycol increased with temperature as 1,2-propanediol reacted further to these products due to C–C bond cleavage. This was also observed when the hydrogen content was increased at constant temperature (250 °C). All catalysts were found to be stable in terms of activity and selectivity to lower alcohols over a period of at least 24 hours at 250 °C and 60 bar H2 pressure.

Effect of O2, CO2 and N2O on Ni–Mo/Al2O3 catalyst oxygen mobility in n-butane activation and conversion to 1,3-butadiene

A commercial heterogeneous Ni–Mo/Al2O3 catalyst was tested for the oxidative dehydrogenation (ODH) reaction of n-butane with different oxidant species: O2, CO2 and N2O. The effect of the lattice oxygen mobility and storage in Ni–Mo/Al2O3 on catalytic conversion performance was investigated. Experiments indicated that a high O2-storage/release is beneficial for activity, however at the expense of selectivity. A significant amount of butadiene with no oxygenated compound products was formed upon using carbon dioxide and nitrous oxide, while O2 favoured the formation of cracked hydrocarbon chains and COx. The highest turnover yield to 1,3-butadiene was achieved at an oxidant-to-butane molar ratio of 2 : 1 at temperatures of 350 °C and 450 °C. With CO2, significant amounts of hydrogen and carbon monoxide have evolved due to a parallel reforming pathway. Partial nickel/molybdenum oxidation was also observed under CO2 and N2O atmospheres. TPR revealed the transformation of the high valence oxides into structurally distinct metal sub-oxides. In TPRO, three distinct peaks were visible and ascribed to surface oxygen sites and two framework positions. With N2O, these peaks shifted towards a lower temperature region, indicating better diffusional accessibility and easier bulk-to-surface migration. XRD revealed the presence of an α-NiMoO4 active phase, which was used in DFT modelling as a (110) plane. Theoretical ab initio calculations elucidated fundamentally different reactive chemical intermediates when using CO2/N2O or O2 as the oxidant. The former molecules promote Mo atom oxygen termination, while in an O2 environment, Ni is also oxygenated. Consequently, CO2 and N2O selectively dehydrogenate C4H10 through serial hydrogen abstraction: butane → butyl → 1-butene → 1-butene-3-nyl → butadiene. With O2, butane is firstly transformed into butanol and then to butanal, which are prone to subsequent C–C bond cleavage. The latter is mirrored in different mechanisms and rate-determining steps, which are essential for efficient butadiene monomer process productivity and the optimisation thereof.

Ternary (Cu, Ni and Co) Nanocatalysts for Hydrogenation of Octanal to Octanol: An Insight into the Cooperative Effect

Ternary metal oxides (Cu–Ni–Co) with different wt% loadings were supported on alumina by using an ultrasonic cavitation-impregnation method. A comparative silica catalyst was also prepared. Powder X-ray diffraction (XRD) showed the presence of the metal oxides on the surface of the supports and from in situ XRD results, the formation of metallic phases under a reducing atmosphere were observed. Temperature-programmed desorption (TPD) revealed the presence of Lewis and Brønsted acidic sites in the catalysts. The metals supported on alumina showed a better dispersion compared to that on the silica support. All the catalysts were tested for the hydrogenation of octanal in a mixture of 10% octanal in octanol in a continuous flow fixed bed reactor by varying the pressure, temperature and hydrogen molar ratios. Under the hydrogenation conditions, the trimetallic catalysts (with Cu, Ni and Co) showed best catalytic performance for octanal hydrogenation when compared to bimetallic catalysts. The conversion of octanal and the selectivity towards octanol increased in proportion to an increase in the total metallic content and metal dispersion. The alumina based catalysts showed better activity compared to the silica catalyst due to higher metal dispersion. The silica supported catalyst showed a high selectivity towards C24 acetal due to its higher acidity and the product distribution over all the catalysts is in agreement with the distribution of acidic sites.Graphical Abstract

Oxidative Dehydrogenation of n-Octane over Niobium-Doped NiAl2O4: An Example of Beneficial Coking in Catalysis over Spinel

NiAl2O4‐based materials are known as enhanced catalysts for several catalytic applications that have coke deposition in common. In this study, Nb as a dopant was found to occupy the octahedral sites of the spinel preferably. As a result, the cation distribution was altered between the two sub‐lattices of the cubic spinel. Therefore, ordered modifications of nickel migration, electronic profile, redox properties and surface textures were observed for these catalysts. Also, coke deposition over these catalysts was controlled using Nb doping and found to modify the original features of the fresh catalysts and lower their crystallite sizes. This study suggests reasons why NiAl2O4 spinel performs so well in the majority of the high‐temperature catalytic processes that suffer from coke deposition.