Catalysts For Partial Oxidation Research Articles

In Situ FMR Study of the Selective H2S-Oxidation Stability of ε-Fe2O3/SiO2 Catalysts

The stability of a catalyst for partial H2S oxidation has been studied by the ferromagnetic resonance (FMR) technique combined with transmission electron microscopy, X-ray diffraction, Mossbauer spectroscopy, and magnetostatic investigations. The e-Fe2O3 iron oxide nanoparticles supported on silica have been examined for their stability under the selective H2S oxidation conditions. The combination of the physicochemical methods has been used to study the state of reacted catalysts. The e-Fe2O3 phase has been found to remain stable under the selective H2S oxidation conditions at temperatures up to 300 °C. The active phase state during the catalytic reaction has been explored using in situ FMR experiments. It has been established that the e-Fe2O3 nanoparticles retain their structure and magnetic properties in the presence of H2S at high temperatures. During the in situ FMR experiments, the e-Fe2O3 sulfidation process has been studied.

New Metal Oxide Composite Materials as Efficient Catalysts of Partial Oxidation of Methane

New Metal Oxide Composite Materials as Efficient Catalysts of Partial Oxidation of Methane

Performance evaluation of NiCo2O4 spinel as a catalyst for partial oxidation of methane

The NiCo2O4 catalyst with spinel structure was prepared by a modified polymeric-precursor method using gelatin as an organic-directing agent. The obtained powder was characterized by XRD, TPR and tested on the partial oxidation of methane. The Rietveld analysis performed on the XRD pattern confirmed the crystallization of two phases, the spinel NiCo2O4, and a solid solution NixCo1-xO. TPR profile revealed that both phases are entirely reduced up to 610 °C. The catalyst showed CH4 conversion of 75 % with H2/CO ratio around 2 and no signal of deactivation by coke formation, such as confirmed by XRD and TG analysis carried out after the catalytic test. Keywords: NiCo2O4, gelatin, partial oxidation of methane.

Morphological and Physical Study of La0.7Sr0.3Co0.2Fe0.8O3-δ (LSCF 7328) Flat Membranes Modified by Polyethylene Glycol (PEG)

The aim of this work is to study the effect of polyethylene glycol (PEG) on the modification of microstructure formation correlated with the mechanical strength properties of perovskite-based membrane in form of a flat sheet. LSCF 7328 flat membrane was potentially promoted as an oxygen separator and catalyst for partial oxidation of methane reaction at high temperature. In this study, the phase-inversion followed by sintering process was used as the membrane fabrication method using varied PEG concentration of 0.55, 1.00, and 3.00 wt% with different molecular weight, i.e., PEG 300, 600, 1500, and 4000 Da for each PEG concentration. The result of morphology observation shows that almost every membrane hasthe asymmetric structure with finger-like pores and thin dense layer. Increasing PEG concentration as well as molecular weight increases pore size and affects on porosity, pore's volume, and physical properties of membrane. The largest pore size, pore volume and porosity of the membrane after sintering were found in the addition of 3.00% PEG 4000 (Da) additive with the value of 110.45 μm, 81.34 ml.g-1 and 120.6%, respectively. In addition, the mechanical properties of membrane were tested using the Vickers micro hardness method with the greatest value found in the addition of 3.00% PEG 1500 (Da) additive with the value of 13.58 Hv and the lowest is 3.00% PEG 4000 (Da) with the value of 1.2 Hv.

Catalytic partial oxidation of CH4 to syn gas (H2/CO) in presence of N2O over periclase type SiO2@Ni(Mg,Al)O catalyst synthesized by non aqueous route

Periclase type Ni/Mg/Al mixed-metal oxide prepared from sol-gel derived SiO2@Ni-Mg-Al Layered Double Hydroxides (LDH) nanocomposite at SiO2:LDH ratios 0:1 and 1:1 was used as a catalyst for catalytic partial oxidation (CPO) of CH4 in presence of N2O as well as oxygen. The catalysts were characterized by XRD, BET surface area, H2-TPR and XPS analysis. The presence of SiO2 dispersant influenced the catalytic property. The nascent oxygen formed by the decomposition of N2O does not re-oxidize Ni0 like molecular oxygen which act as the active species and leads to partial oxidation of CH4. SiO2@Ni-Mg-Al (1:1) catalyst showed about 99.99% H2 and 99.8% CO yield between the temperature range of 200-500 °C.

Mars van Krevelen Mechanism for the Selective Partial Oxidation of Ethane

Abstract Ethylene is the most important olefin in the petrochemical context, since it is the main raw material for the production of many polymers. Traditional production of ethylene via thermal cracking and catalytic dehydrogenation consumes large amounts of energy; hence selective partial oxidation of ethane has been considered as an attractive alternative production path. Recently, development of a promising catalyst for selective partial oxidation of ethane, which consists of multi-metallic mixed oxides of Mo, Te, V, and Nb, has been published. It is also noteworthy that this catalytic system starts to be active at temperatures below 400 °C, substantially lower than the one required by commercial thermal processes, >800 °C. In this work, a kinetic mechanism based on Mars van Krevelen formalism is proposed for the selective partial oxidation of ethane, considering the surface itself as active protagonist of the reaction. RedOx steps on active sites are considered as the controlling ones, and the rest of transformations are considered as pseudo-steady steps. It is noticed that there are side reactions, which produces CO and CO2 as combustion by-products. Additionally, there is competition for reduced sites on the catalytic surface, mainly between oxygen and water molecules, which adsorb strongly on these sites. Adjusted results by the mechanism proposed are in agreement with experimental observations of reaction rates diminishing proportionally to partial pressure of water, caused by competition of reduced sites on catalyst surface.

Heterogeneous Catalytic Oxidation of Amides to Imides by Manganese Oxides

Herein, we report a one-step peroxide mediated heterogeneous catalytic oxidation of amides to imides utilizing a series of manganese oxides. Among them, Cs/Mn2O3 was found to be the most active catalyst for the selective partial oxidation of N-benzylbenzamide to diphenyl imide. We have been able to apply an optimized oxidation method to other aromatic substrates. The feasibility of using air as an oxidant, the heterogeneous nature, inexpensive catalytic materials, respectable turnover numbers, and chemoselectivity to imides make this methodology an attractive choice for functional group transformations of amides to imides.

Rational Design of High Surface Area Mesoporous Ni/CeO2 for Partial Oxidation of Propane

A Ni loaded catalyst on mesoporous ceria, with a large surface area, prepared through the surfactant-assisted precipitation and impregnation method was investigated as an efficient catalyst for propane partial oxidation to produce synthesis gas. The results show that 2.5 wt% Ni/CeO2 had the optimum Ni loading, exhibiting the highest catalytic propane conversion. It also showed excellent stability, with no obvious activity drop after a 10 h time-on-stream reaction and slightly decreased in H2 and CO yields. The investigation of the reactant composition effect on carbon formation showed that by decreasing the C/O2 ratio the content of accumulated carbon decreased and propane conversion increased. The good activity of the Ni/CeO2 can be ascribed to the high surface area and rich surface defects of the ceria support and a high dispersion of active sites (Ni nanoparticles).

Statistically Guided Synthesis of MoV-Based Mixed-Oxide Catalysts for Ethane Partial Oxidation

The catalytic performance of Mo8V2Nb1-based mixed-oxide catalysts for ethane partial oxidation is highly sensitive to the doping of elements with redox and acid functionality. Specifically, control over product distributions to ethylene and acetic acid can be afforded via the specific pairing of redox elements (Pd, Ni, Ti) and acid elements (K, Cs, Te) and the levels at which these elements are doped. The redox element, acid element, redox/acid ratio, and dopant/host ratio were investigated using a three-level, four-factor factorial screening design to establish relationships between catalyst composition, structure, and product distribution for ethane partial oxidation. Results show that the balance between redox and acid functionality and overall dopant level is important for maximizing the formation of each product while maintaining the structural integrity of the host metal oxide. Overall, ethylene yield was maximized for a Mo8V2Nb1Ni0.0025Te0.5 composition, while acetic acid yield was maximized for a Mo8V2Nb1Ti0.005Te1 catalyst.

Alkali and earth alkali modified CuOx/SiO2 catalysts for propylene partial oxidation: What determines the selectivity?

In this work, CuOx/SiO2 catalysts were investigated in the propylene partial oxidation reaction. Ordered mesoporous silica (KIT-6) was used to deposit 1–10 wt. % copper and subsequently modified with Na, K and Ca. The synthesized materials were characterized by N2 physisorption, XRD, TEM-EDS, CO2-TPD, operando UV/Vis DRS, operando XANES and pyridine DRIFT spectroscopy. Regardless of the CuOx loading, catalyst deactivation was observed during propylene oxidation reaction in non-modified catalysts, which was related to sintering of oligomeric [Cu-O-Cu]n species. Sintering of CuOx is strongly promoted under a reducing propylene atmosphere and related to the presence of Cu+1. The resulting bulk CuOx promotes acrolein selectivity. We produced modified catalysts with finely dispersed alkali metal cations, associated with the subnanometer CuOx phase, resulting in a greatly stabilized morphology and catalytic activity. Operando XANES analysis revealed that a substantial fraction of Cu2+ is transformed to Cu+ during the propylene oxidation reaction (52–68%, depending on the modifying atom). Also, the dynamics of reaching the quasi steady oxidation state differ strongly. The kinetics of oxygen abstraction and replenishment are substantially different, indicative of modified chemistry of the nucleophilic oxygen species, present in 5CuNa catalyst in contrast to others (5Cu and 5CuCa). We propose that Cu+ is not crucial for PO formation. Instead the electropositive Na+ and K+ decrease the nucleophilic strength of oxygen in CuOx, by attracting its electrons. Consequently, the catalytic action of oxygen changes from oxidative attack on the allylic hydrogen to oxygen insertion into the CC bond of propylene. This results in a noticeable selectivity shift from acrolein to propylene oxide. The effect of calcium on decreasing the nucleophilic character of O species in CuOx is negated by charge compensation by strongly adsorbed hydroxyl groups and Ca modification for PO selectivity is inefficient. Additionally we found, that further oxidation of propylene oxide is, most likely, the main factor determining high selectivity for COx products. The alkali modification which increases the PO selectivity does not function via elimination of LAS, but exclusively through attenuation of nucleophilic character of oxygen species.

The Compatibility of NiO, CeO2 and NiO-CeO2 as a Coating on La0.6Sr0.4Co0.2Fe0.8O3-δ, La0.7Sr0.3Co0.2Fe0.8O3-δ and La0.7Sr0.3Mn0.3O3-δ Ceramic Membranes and Their Mechanical Properties

Metal oxides and perovskites have got tremendous attention as a good catalyst for partial oxidation of methane (POM). In the present work, the materials were cast into a double layer planar membrane using the dry pressing method in order to enhance its’ catalytic activity. Unfortunately, the majority of metal oxides and perovskites have different thermal expansion coefficient (TEC). Therefore, this work was aimed to study the compatibility between catalyst metal oxides (NiO, CeO2) and perovskite oxides La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF 6428), La0.7Sr0.3Co0.2Fe0.8O3-δ (LSCF 7328) and La0.7Sr0.3MnO3-δ (LSM 73) when they were made as double layer membranes. The result shows that the density and volume shrinkage of LSCF 7328 was the highest, followed by LSM 73 and LSCF 6428. It was also found that the trends of hardness and density in the perovskites and metal oxides follows their thermal expansion trends. According to thermomechanical analysis (TMA) results, TEC of LSCF 6428, LSCF 7328, LSM 73, NiO-CeO2, NiO and CeO2 were 22.16; 9.31; 10.14; 12.21; 20.86 and 21,11 ppm/°C, respectively. From the TEC data, Large differences in TEC cause the delamination of NiO, CeO and mixtures of NiO-CeO2 from perovskite surface except those who were prepared using amylum as a binder in the preparation of double layer membranes.

Support effect of Ag/ZnO catalysts for partial oxidation of methanol

Three ZnO supports with different morphologies (fusiform, nanoparticle and rod-shaped sphere) were synthesized successfully by facile hydrothermal method, over which Ag were loaded to evaluate for the hydrogen production in partial oxidation of methanol in the temperature range of 150–400°C. The activity data showed that the catalytic activities of Ag/ZnO catalysts were markedly affected by the morphologies of the supporting materials, among which their activities ranked as fusiform>nanoparticle>rod-shaped sphere. The best performing AgZn-F catalyst shows the highly efficient catalytic performance, achieving almost 100% conversion and very low CO selectivity at 360°C. These results illustrate that the morphology of support plays a crucial role on the Ag dispersion and the interaction of Ag and ZnO support, and thus determines the catalytic activity in partial oxidation of methanol.

Behaviour of Rh supported on hydroxyapatite catalysts in partial oxidation and steam reforming of methane: On the role of the speciation of the Rh particles

Rh/hydroxyapatite samples were prepared by impregnation and investigated for the partial oxidation (POM) and steam reforming (SRM) of methane. The catalysts were analysed by BET, XRD, DRS, XPS, H2-TPR, TEM, H2 chemisorption, CO2-TPD and NH3-TPD techniques. The characterisation results showed that, after calcination, Rh existed in three different forms in the samples: (i) large crystallites of Rh2O3 deposited on the surface of the catalysts, (ii) RhOx in small particles exhibiting strong interaction with the support and (iii) a phase of Rh2+ species which incorporated the hydroxyapatite framework.Operating in the POM and SRM processes the reduced Rh(x)/HAP catalysts resulted highly active and exhibited excellent stability at 973 K (for 30 h). This behaviour was explained by their high coke-resistance. The activity of the catalyst with the optimum loading (1%), in SRM, was compared with that of a commercial Rh/Al2O3 catalyst. The conversion and H2 and CO yields values achieved on the former were all close to those exhibited by the latter. This comparable behaviour was explained by suitable properties provided by the HAP support such as reducibility, lower surface acidity and larger pore sizes (ensuring a better diffusion of the reactants and the products during the SRM reaction). These properties seemed to compensate the low dispersion of the Rh active phase induced by its low specific surface area.

Effect of copper and cerium on the performance of Ni-SBA-16 in the partial oxidation of methane

In this research, the effect of Ce, Cu and Ce–Cu promoters on the performance of Ni/SBA-16 catalyst in partial oxidation of methane reaction was investigated. The Ni/SBA-16 catalyst with 9.1 wt% Ni content without promoter and Ni/SBA-16 catalyst promoted with cerium, copper, copper–cerium with equimolar to nickel content were prepared and their performance in methane partial oxidation reaction were evaluated. The prepared catalysts were characterized by XRD, N2 adsorption and EDX-FESEM analysis techniques. The N2 adsorption isotherms of catalyst samples showed that adding promoters to the Ni/SBA-16 catalyst partly decreased the surface area of catalysts. Furthermore, the results using XRD analysis partly demonstrated dispersion of nickel particle for catalyst Cu-promoted. Also, SEM analysis showed a similar size of nano crystallites in the range of 8–20 nm for all catalyst samples. The results of evaluation of catalytic activities of the catalysts showed high activity of unpromoted and Ce-promoted nickel catalyst in methane conversion (≈ 93%) remained stable for 3 h. The effects of other reaction parameters such as temperature, gas hourly space velocity and molar ratio of the feed were also evaluated and reported.

Catalytic Activity Studies of Vanadia/Silica–Titania Catalysts in SVOC Partial Oxidation to Formaldehyde: Focus on the Catalyst Composition

In this work, silica–titania supported catalysts were prepared by a sol–gel method with various compositions. Vanadia was impregnated on SiO2-TiO2 with different loadings, and materials were investigated in the partial oxidation of methanol and methyl mercaptan to formaldehyde. The materials were characterized by using N2 physisorption, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), Scanning transmission electron microscope (STEM), NH3-TPD, and Raman techniques. The activity results show the high importance of an optimized SiO2-TiO2 ratio to reach a high reactant conversion and formaldehyde yield. The characteristics of mixed oxides ensure a better dispersion of the active phase on the support and in this way increase the activity of the catalysts. The addition of vanadium pentoxide on the support lowered the optimal temperature of the reaction significantly. Increasing the vanadia loading from 1.5% to 2.5% did not result in higher formaldehyde concentration. Over the 1.5%V2O5/SiO2 + 30%TiO2 catalyst, the optimal selectivity was reached at 415 °C when the maximum formaldehyde concentration was ~1000 ppm.

Thermally stable core-shell Ni/nanorod-CeO2@SiO2 catalyst for partial oxidation of methane at high temperatures.

During partial oxidation of methane (POM), the greatest challenge is to maintain the thermal stability of the catalyst at high temperatures. One of the most effective ways to improve thermal stability is to construct core-shell structure. Herein, using a microemulsion method, we synthesized a core-shell Ni/nanorod-CeO2@SiO2 catalyst, in which the Ni nanoparticles were supported on the CeO2 nanorods and encapsulated by SiO2 shells. Based on a series of characterizations, we found that the Ni particles are of nanosize (2.2 nm) and the thickness of the SiO2 shell is about 8 nm in the core-shell catalyst. Moreover, the Ni/nanorod-CeO2@SiO2 catalyst can perfectly maintain rod-like structures of the CeO2 support and enhance interaction between the metal Ni and CeO2, significantly reducing the sintering of metal Ni particles at high temperatures. Therefore, the as-prepared Ni/nanorod-CeO2@SiO2 catalyst shows high catalytic activity and good thermal stability during the POM reaction.

Molybdenum dioxide as an alternative catalyst for direct utilization of methane in tubular solid oxide fuel cells

Direct utilization of methane in conventional tubular solid oxide fuel cells (SOFCs) with a Ni-YSZ anode support was proposed using MoO2 as a partial oxidation catalyst for methane reforming at the cell inlet. A promising stability was achieved for a continuous operation in a mixture of methane and air (1, 1.5) for >150h under a load voltage of 0.7V at 750°C. The addition of the MoO2 catalyst at the anode inlet made tubular SOFCs with the conventional Ni-YSZ anode an efficient and practically promising candidate for direct hydrocarbon utilization.

Partial oxidation of alkanes by dioxiranes formed in situ at low temperature.

Partial oxidation catalysts capable of efficiently operating at low temperatures may limit the over-oxidation of alkane substrates and thereby improve selectivity. This work focuses on examining alkane oxidation using completely metal-free organocatalysts, dioxiranes. The dioxiranes employed here are synthesized by oxidation of a ketone using a terminal oxidant, such as hydrogen peroxide. Our work generates the dioxirane in situ, so that the process can be catalytic with respect to the ketone. To date, we have demonstrated selective partial oxidation of adamantane using ketone catalysts resulting in yields upwards of 60% towards 1-adamantanol with greater than 99% selectivity. Furthermore, we have demonstrated that changing the electrophilic character of the ketone R groups to contain more electron-donating ligands facilitates the dioxirane ring formation and improves overall oxidation yields. Isotopic labelling studies using H218O2 show the preferential incorporation of an 18O label into the parent ketone, providing evidence for a dioxirane intermediate formed in situ The isotopic labelling studies, along with solvent effect studies, suggest the formation of peracetic acid as a reactive intermediate.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol: Influence of solution pH, Au nanoparticle size, support structure and acidity

Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1nm.

Cu doped amine functionalized graphene oxide and its scope as catalyst for selective oxidation

We describe the synthesis of Cu doped amine functionalized graphene oxide (Cu@AGO) and its effective application as recyclable heterogeneous catalyst for selective partial oxidation of benzyl alcohols to corresponding benzaldehydes under mild conditions with acetonitrile as solvent. The Cu@AGO was fully characterized by XRD, FT-IR, Raman spectra, XPS, SEM and TEM analysis. FT-IR validated the successful grafting of organic amine with graphene oxide, while TEM confirmed the uniform distribution of metal particles on amine functionalized graphene oxide. The catalyst gave excellent conversion (92%) and selectivity (99%) towards benzaldehyde, with good reusability up to 4cycles.