SiO2 Catalysts Research Articles

Room Temperature Ultrafast Oxidative Desulfurization with Sodium Hypochlorite in the Presence of Silica-Supported Catalysts.

A series of silica-supported catalysts containing molybdenum, tungsten, and vanadium oxides as the active phase was investigated in the process of oxidative desulfurization with sodium hypochlorite. It was shown for the first time that catalysts containing vanadium oxide as the active phase are more stable under oxidation conditions with sodium hypochlorite and retain their effectiveness at increased dosages of the oxidant and at high initial sulfur contents. The catalysts were characterized in detail by a complex of methods: Fourier transform infrared, X-ray spectral fluorescence, transmission electron microscopy, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. Key factors affecting the oxidation of dibenzothiophene (DBT) were investigated: oxidant and catalyst amount, oxidation time, initial sulfur content, and acetonitrile amount. Under optimized conditions, the DBT conversion rate was 100% in 5 min at room temperature (25 °C), NaClO/S molar ratio 6:1, catalyst amount 2 wt %. In the real sample of the straight-run diesel fraction, the sulfur content was reduced from 10,100 to 3030 ppm. The V(10%)/SiO2 catalyst retains its activity for 5 oxidation-regeneration cycles.

High-Pressure oxidative coupling of methane on alkali metal catalyst – Microkinetic analysis and operando thermal visualization

To introduce promotional H2O effects for both CH4 rate and C2 selectivity, the OH radical formation, catalyzed through H2O activation with O2 surface species, was critical for modeling selective Mn-K2WO4/SiO2 catalysts. Based on our reported experimental evidence, which demonstrates the formation of H2O2 through surface alkali peroxide intermediate, the elementary reactions that account for the OH-mediated pathway were added into the microkinetic model. The advanced model adeptly replicated the promotional H2O effects on both OCM rate and selectivity. The data from a low-pressure microkinetic study were treated isothermally, and extended for near-industrially relevant pressures up to 901 kPa. Thermal visualization using an infrared camera found substantial temperature increases at undiluted high-pressure conditions which caused C2 selectivity to drop significantly. When the furnace temperatures were decreased after ignition, side reactions after O2 depletion (e.g., hydrocarbon reforming) were suppressed, obtaining 13.7 (11.8) % yields at 19.9 % CH4 conversion with 68.6 (59.1) % selectivities for C2-4 (C2) at 901 kPa. The temperature was found to be the determining factor of C2 yield which was perturbed by varying space velocity or CH4/O2 ratios. The optimum temperature for high-pressure conditions was predicted as 885 °C at 901 kPa. The study provides mechanistic and industrially relevant understandings for further OCM catalyst design and system application.

Catalytic wet peroxide oxidation of organic dye with in-situ generated H2O2 over bifunctional Fe-Pt@Pd/SiO2 catalyst prepared by double-metal complex salt approach

While the Fenton reaction is efficient in wastewater treatment, the intrinsic problem of the dosage-dependent process poses another burden on ecosystem. Herein, we propose a highly efficient and environmentally-benign catalytic wet peroxide oxidation (CWPO) of methyl orange (MO) using in-situ generated H2O2 from hydrogen and air instead of ready-made H2O2. Pt@Pd/SiO2 and Pd@Pt/SiO2 catalysts were prepared by double-metal complex salt approach, and they were combined with soluble Fe salt (CWPO-I) or impregnated Fe (CWPO-II). The MO degradation rate of Pt@Pd/SiO2 for CWPO-I was 2.5 times faster than that of the conventional PdPt/SiO2. This can be rationalized in terms of Pd-enriched surface with strong interaction between Pt and Pd. Moreover, bifunctional Fe-Pt@Pd/SiO2 catalyst demonstrated outstanding activity in promoting CWPO-II with in-situ generated H2O2, even outperforming its counterpart with ready-made H2O2. This new approach offers an efficient water remediation method free from addition and generation of any undesirable chemicals affecting environment.

A bifunctional cobalt catalyst for the synthesis of waxy diesel fuel by the Fischer–Tropsch method – from the development to implementation. Part 3. The experience of industrial implementation of the preparation technology

The work summarizes the results of testing the technology for preparing a bifunctional cobalt catalyst for the synthesis of hydrocarbons from CO and H2, obtained by extruding a mixture of Co-Al2O3 /SiO2 catalyst powders and HZSM-5 zeolite with a binder – boehmite in industrial conditions (2 batches of 50 kg each were prepared). The catalyst technology was implemented on the equipment of Ishimbay Specialized Chemical Catalyst Plant LLC. The obtained industrial samples of the catalyst were characterized by XRF, TPR H2, DTG, and tested in the synthesis of hydrocarbons from CO and H2 at a temperature of 250 °C, a pressure of 2.0 MPa, GHSV 1000 h–1. It has been shown that the implementation of the technology of a bifunctional cobalt catalyst for the production of low pour point diesel fuel in industrial conditions makes it possible to reproduce the characteristics of the catalyst obtained in laboratory conditions. The technology for producing the catalyst can be recommended for the production of industrial batches. It was determined that changes in the heat treatment conditions of the catalyst, as well as the presence/absence of a peptizer and pore former do not lead to a significant decrease in the productivity of C5+ hydrocarbons. The contentof the diesel fraction in C5+ products obtained from industrial samples of the catalyst remains at the level of the value obtained from the laboratory sample of the catalyst. At the same time, the low-temperature properties of diesel fuel obtained using all catalyst samples have similar values. Using an industrial sample synthesized without the use of a peptizing agent and a pore-forming component, the best lowtemperature properties of diesel fuel were achieved – the cloud point and fluid loss point were minus 16 and minus 24, respectively.

An Analysis of Fixed-Bed Catalytic Reactors Performances for One-Stage Butadiene Synthesis from Ethanol

The present study assesses, using a theoretical approach, the performances of two widely used fixed-bed reactors for the ethanol-to-butadiene (ETB) one-stage (Lebedev) process: multibed adiabatic reactors (MBAR) with inter-bed heating and a multitubular reactor (MTR). The mathematical model consists of mass and heat conservation equations at catalyst particle and particle bed scales, coupled with a published kinetic model specific for a modified MgO–SiO2 catalyst. The process simulations at the level of catalyst particle have shown that the inter-phase concentration and temperature gradients are negligible, the only physical step with a limiting influence on process kinetics being the internal diffusion. A simplified version of the reactor model was also formulated, including empirical expressions developed in the study for the calculation of internal effectiveness factors. The reactor simulations highlighted that the MBAR with inter-bed heating by injection of hot reactants provides worse butadiene (BD) yields as a consequence of reduced reaction times (due to reactant by-pass of catalyst beds). The MBAR with inter-bed heating using heat exchangers provides better performances but inferior to those of MTR if the number of catalyst beds is less than six. A preliminary optimization study for the MBAR and MTR is also presented. The results showed that the maximization of BD yield has the drawback of a low BD production rate, whereas the maximization of BD production rate corresponds to a relatively low BD yield and high ethanol and inert recycles. A trade-off between the two extreme cases can be attained by maximizing the income generated by reactor operation.

Modulation of supported Ni catalysts with phosphorus for the hydrogenation of diethyl oxalate to ethyl glycolate

The presence of P affects the surface metal states of catalysts, which, in turn, has an effect on their substrate adsorption states and ultimately their catalytic performance.

Core–shell structured magnesia–silica as a next generation catalyst for one-step ethanol-to-butadiene Lebedev process

Over 70 years, silica–magnesia catalyst prepared by wet-kneading method has been a benchmark for one-step ethanol-to-butadiene Lebedev process. Recent studies showed that wet-kneading provides an environment for the concomitant dissolution and cross-deposition of silicon and magnesium subunits, which can lead to the formation of not only the beneficial sites (Si on MgO), but also the detrimental ones (Mg on SiO2) for the Lebedev process. The use of conventional silica sources to formulate the silica–magnesia catalysts should be revisited, as they will be eventually dissolved and redispersed on MgO and the remaining SiO2 particles would be used for the formation of detrimental sites. In this regard, we demonstrated core–shell structured MgO–SiO2 catalysts as a second generation of Lebedev catalyst, where the Si subunits were selectively deposited on the MgO nanoparticles as surface magnesium silicates. Compared to the conventional wet-kneaded silica–magnesia catalyst system, we could reduce the amount of Si source by ∼40 times with the enhanced catalytic performance towards butadiene.

CrOx–SiO2 Catalysts in Nonoxidative Propane Dehydrogenation: Effect of Adding Cerium Dioxide

CrOx–SiO2 Catalysts in Nonoxidative Propane Dehydrogenation: Effect of Adding Cerium Dioxide

Unlocking a Dual-Channel Pathway in CO2 Hydrogenation to Methanol over Single-Site Zirconium on Amorphous Silica.

Converting CO2 into methanol on a large scale is of great significance in the sustainable methanol economy. Zirconia species are considered to be an essential support in Cu-based catalysts due to their excellent properties for CO2 adsorption and activation. However, the evolution of Zr species during the reaction and the effect of their structure on the reaction pathways remain unclear. Herein, single-site Zr species in an amorphous SiO2 matrix are created by enhancing the Zr-Si interaction in Cu/ZrO2 -SiO2 catalysts. In situ X-ray absorption spectroscopy (XAS) reveals that the coordination environment of single-site Zr is sensitive to the atmosphere and reaction conditions. We demonstrate that the CO2 adsorption occurs preferably on the interface of Cu and single-site Zr rather than on ZrO2 nanoparticles. Methanol synthesis in reverse water-gas-shift (RWGS)+CO-hydro pathway is verified only over single-dispersed Zr sites, whereas the ordinary formate pathway occurs on ZrO2 nanoparticles. Thus, it expands a non-competitive parallel pathway as a supplement to the dominant formate pathway, resulting in the enhancement of Cu activity sixfold and twofold based on Cu/SiO2 and Cu/ZrO2 catalysts, respectively. The establishment of this dual-channel pathway by single-site Zr species in this work opens new horizons for understanding the role of atomically dispersed oxides in catalysis science.

Unlocking a Dual‐Channel Pathway in CO2 Hydrogenation to Methanol over Single‐Site Zirconium on Amorphous Silica

AbstractConverting CO2 into methanol on a large scale is of great significance in the sustainable methanol economy. Zirconia species are considered to be an essential support in Cu‐based catalysts due to their excellent properties for CO2 adsorption and activation. However, the evolution of Zr species during the reaction and the effect of their structure on the reaction pathways remain unclear. Herein, single‐site Zr species in an amorphous SiO2 matrix are created by enhancing the Zr−Si interaction in Cu/ZrO2‐SiO2 catalysts. In situ X‐ray absorption spectroscopy (XAS) reveals that the coordination environment of single‐site Zr is sensitive to the atmosphere and reaction conditions. We demonstrate that the CO2 adsorption occurs preferably on the interface of Cu and single‐site Zr rather than on ZrO2 nanoparticles. Methanol synthesis in reverse water‐gas‐shift (RWGS)+CO‐hydro pathway is verified only over single‐dispersed Zr sites, whereas the ordinary formate pathway occurs on ZrO2 nanoparticles. Thus, it expands a non‐competitive parallel pathway as a supplement to the dominant formate pathway, resulting in the enhancement of Cu activity sixfold and twofold based on Cu/SiO2 and Cu/ZrO2 catalysts, respectively. The establishment of this dual‐channel pathway by single‐site Zr species in this work opens new horizons for understanding the role of atomically dispersed oxides in catalysis science.

Catalytic combustion of lean methane over different Co3O4 nanoparticle catalysts

Three types of Co3O4 catalyst, namely Co3O4 nanoparticles (denoted as Co3O4-NPs, ∼12 nm in diameter), Co3O4 nanoparticles encapsulated in mesoporou s SiO2 (denoted as Co3O4@SiO2), and Co3O4 nanoparticles inside microporous SiO2 hollow sub-microspheres (denoted as Co3O4-in-SiO2), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co3O4-NPs ≈ Co3O4@SiO2 > Co3O4-in-SiO2 due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co3O4@SiO2 has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO2 layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co3O4@SiO2. In contrast, the microporous SiO2 layer reduces the catalytical activity of Co3O4-in-SiO2 possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO2 layer and catalyst structure are both crucial for the catalytical activity and stability.

Fundamentals of enhanced oxygen releasability of Mn-Na2WO4/SiO2 through cofed water for efficient oxidative coupling of methane in a chemical looping mode

The oxidative coupling of methane (OCM) to C2H6 and C2H4 (C2-hydrocarbons) is an industrially attractive reaction, which has not yet been commercialized. Apart from the low selectivity to C2-hydrocarbons at high degrees of CH4 conversion, another substantial drawback is the necessity to use pure O2 when this oxidant and methane are cofed. Original OCM studies used an approach called chemical looping OCM (CL-OCM) that consists of alternating feeding of methane and air for product formation and catalyst reoxidation, respectively. The developed catalysts, however, suffer from their low ability to provide lattice oxygen for the desired reaction. Herein, we demonstrate that this catalyst property can be significantly improved when performing CL-OCM over Mn-Na2WO4/SiO2 catalysts in the presence of water. In comparison to water-free CL-OCM, both methane conversion and C2-hydrocarbons selectivity increase resulting in at least doubling of the yield of these products. The selectivity to ethylene of about 53 % was obtained at about 24 % CH4 conversion. The total selectivity to C2-hydrocarbons was about 76 %. The analysis of selectivity-conversion relationships for C2H4, C2H6, CO and CO2 proved that water does not alter their general formation pathways but influences the kinetics of their formation.In situ X-ray diffraction, in situ UV–vis spectroscopic, and temperature-programmed tests (H2-TPR and O2-TPD with or without cofed H2O) showed that Mn2O3 acts as the oxygen carrier in CL-OCM. In-situ DRIFTS proved the presence of O2– and O22–. They can interact with water yielding OH radicals that accelerate CH4 conversion.

Dual Pd-acid sites confined in a hierarchical core-shell structure for hydrogenation of nitrobenzene.

A core-shell structured Pd@TS-1@meso-SiO2 catalyst with confined Pd nanometals has been fabricated by one-pot synthesis, impregnation method and sol-gel method. With the promotion of acid sites and protection of mesoporous silica shell, Pd@TS-1@meso-SiO2 shows higher activity than commercial comparison and higher stability than sample without mesoporous silica shell in the hydrogenation of nitrobenzene. The schematic illustration of the synergy effect is also proposed.

Oxidative coupling of biogas to ethylene over a trilobe-shaped Mn-Na2WO4/α-Al2O3 catalyst in a single-pellet reactor

Despite the development of selective catalyst formulations for oxidative coupling of methane (OCM), kinetic and reactor design studies have been hampered by a lack of data for truly isothermal reaction conditions. Because of the high exothermicity, the temperature of a fixed-bed reactor filled with Mn-Na2WO4/SiO2 catalysts will show hot-spots with a loss of selectivity. The objective of this study is to measure catalyst activity under relevant reaction conditions of pressure (3 bar), biogas composition (no dilution) and contact time, while keeping the process isothermal. To this aim, we have synthesized and shaped a trilobed Mn-Na2WO4/α-Al2O3 catalyst, which may be used as is at industrial scale, and measured its performance in a single-pellet reactor. We found that the presence of CO2 did not degrade the catalyst performance, even on the long run, which should enable the use of a CO2-rich stream such as biogas. Actually, higher methane conversions have been obtained in the presence of CO2, likely due to a possible contribution of methane dry reforming reaction. We also noticed a slow catalyst activation over the first 100 h, while selectivity was kept constant.

Decomposition of formic acid over Ni-containing SiO2 catalysts synthesized by various one-pot synthesis routes

Decomposition of formic acid over Ni-containing SiO2 catalysts synthesized by various one-pot synthesis routes

Mn2O3-Na3PO4/TiO2 catalyst with high anti-agglomeration and attrition resistance for fluidized-bed oxidative coupling of methane

The fluidized-bed reactor is a preferred option for the design of an intrinsic-safety oxidative coupling of methane (OCM) process, because it permits such strongly exothermic reaction to proceed isothermally. However, the widely studied Mn-Na2WO4/SiO2 catalyst cannot meet the requirements of the fluidized-bed reaction. Ground-breaking fluid catalyst coupling high activity/selectivity with good anti-agglomeration and high attrition resistance represents a grand challenge. Herein, we report an Mn2O3-Na3PO4/TiO2 catalyst (280–355 μm) for the fluidized-bed OCM process, achieving 28.5% CH4 conversion with 70.1% C2-C3 selectivity at 760 °C for a feed gas of CH4/O2 of 5/1 while remaining unchanged within 16 h test. This catalyst shows significant fluidization behavior under OCM reaction conditions. It is found that TiO2 nanorods tangle up with each other to form an interpenetrating nano-structure thereby inducing strong mechanical strength and robustness with a low attrition index of only 2.8%. Moreover, high melting-point Na3PO4 and use of TiO2 support impart the catalyst to good anti-agglomeration because of eradication of formation of the sticky Na2Si2O5 and molten Na2WO4 (main cause for agglomeration) encountered in the Mn-Na2WO4/SiO2.

Highly Selective Alkaline Oxide Promoted Ni/silica for the Production of Cyclohexanol/‐one from Lignin‐Derived Guaiacol

AbstractCatalytic hydrodeoxygenation (HDO) is a promising route to upgrade bio‐oils from plants or pyrolysis to basic chemicals. KA‐oil (cyclohexanol/‐one) is an example of a highly valuable feedstock for the industrial synthesis of caprolactam and perlon, which can potentially be produced via a completely sustainable route. This work investigates the alkaline promoter effects on Ni‐based catalysts for the selective HDO of lignin surrogate guaiacol using mesoporous Ni/MgO and co‐impregnated Ni‐MgO/SiO2 catalysts. Due to preferred demethoxylation by alkaline oxides and their accumulation on nickel corners, responsible for dehydration, conversion, and selectivity for KA‐oil rise. Furthermore, influences of operating parameters are investigated and optimized by design of experiments (DoE), while long‐term stability (24 h) and water resistance remain high. In a final proof of concept, the application of Ni‐CaO/SiO2 was the most promising material (U=93 %, S=86 %), demonstrating a sustainable route from lignin‐based bio‐oil to produce a bulk commodity for caprolactam synthesis.

Breaking the dilemma of low selectivity in the oxidative coupling of methane over Mn-Na2WO4/SiO2 at low temperatures

Oxidative coupling of methane allows to directly produce higher hydrocarbons (C2-hydrocarbons, mainly C2H6 and C2H4) from cheap and available methane. Although various catalysts have been developed, they operate selectively above 750 °C that is detrimental in terms of reactor construction materials and safe operation. The present study demonstrates that the supported Mn-Na2WO4/SiO2 catalyst achieves the selectivity to C2+-hydrocarbons of 87.3% at methane conversion of 6.6% at 675 °C only. With the aid of sophisticated kinetic measurements, the origins of this unexpectedly high performance have been elucidated. When operating with water-containing feeds, the reaction order of the rate of C2H6 formation with respect to O2 at 675 °C is practically zero in the presence of water, while the corresponding values for CO and CO2 are 0.9 and 0.7. Moreover, O2 partial pressure is also decisive for the strength of the enhancing water effect. The water-induced increase in the rate of CH4 conversion into C2-hydrocarbons can be about 120 times using a feed with the ratio of CH4/O2 of 24. The corresponding enhancement factors for the formation of CO and CO2 are only 20 and 6, respectively. These new fundamentals provide hints for optimizing reactor operation for efficient conversion of methane into C2+-hydrocarbons at low temperatures.

One‐pot synthesis of V doped mesoporous SiO2 catalysts for selective oxidation of ethane and propane

AbstractA series of vanadium‐doped mesoporous SiO2 catalysts were prepared using a one‐pot emulsion method. The effects of VOx species with different structures on C−H bond activation and product selectivity in ethane and propane selective oxidation were investigated using X‐ray diffraction (XRD), N2 adsorption‐desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, ultraviolet‐visible diffuse reflectance spectroscopy (UV‐Vis DRS), hydrogen temperature programmed reduction (H2‐TPR), and ammonia temperature programmed desorption (NH3‐TPD) characterizations. The results revealed that the highly dispersed isolated tetrahedral VOx species on the catalyst gradually polymerized into highly dispersed oligomeric VOx species with the increased V loading. The former is beneficial for the formation of olefins and total aldehydes during the selective oxidation of propane. Oligomeric VOx species are conducive to improving the selectivity of ethylene and acetaldehyde in the selective oxidation of ethane. The highest catalytic performances for selective oxidation of ethane and propane were obtained at a temperature of 650 °C. The conversion of ethane was 41.6 %, with a corresponding yield of ethylene and acetaldehyde of 23.6 % over a 0.5 V−SiO2 catalyst. In contrast, the propane conversion was 61.5 %, with a corresponding total yield of olefins and aldehydes of 41.3 % over a 1.0 V−SiO2 catalyst.

Silica‐Confined Ru Species Highly Dispersed on the Porous Ce‐Modified ZrO2 Matrix with Different Redox and Acidity Properties for the Catalytic Combustion of 1,2‐Dichloroethane

AbstractThe RuO2@CemZr1−mO2−SiO2 catalysts were synthesized by the spontaneous deposition method. Based on the XRD patterns of various RuO2@CemZr1−mO2−SiO2 catalysts, it was suggested that the Ru noble metal nanoparticles were distributed with high dispersion on the surface of Ce‐modified porous matrix of ZrO2. H2‐TPR and NH3‐TPD confirmed that all catalysts possessed superior redox ability as well as acidity, which were facilitated to the catalytic dichloroethane (DCE) oxidation. From the systematic study of texture structure, surface properties and catalytic activity, we knew that acid sites were shown to be favorable for adsorption as well as activation of DCE and improve the anti‐poisoning property of the catalyst, and the redox ability could facilitate the further oxidation of the intermediate. The optimized RuO2@Ce0.1Zr0.9O2−SiO2 catalyst exhibited superior activity (T90=275 °C at a space velocity of 15000 h−1), good stability (at 300 °C for 50 h) and outstanding tolerance towards moisture (in 5 % moisture). Our work demonstrated the important role of acidity and redox ability over these functionalized catalysts, providing guidance for the advanced catalyst design.