In this study, the asphaltene extracted from Luntai heavy oil was oxidized by a mixture of propionic anhydride and hydrogen peroxide without and with a catalyst. Elemental analysis and infrared ...spectroscopy results indicated the occurrence of oxygen addition, condensation, and side chain cleavage reactions in the oxidation process. Oxidation products were divided into methanol solubles and methanol insolubles. The H/C and O/C atomic ratios of the MeOHS in the oxidation products without a catalyst were higher than those of the Luntai asphaltene. MeOHS had fewer aromatic rings than Luntai asphaltene. Compared with the oxidative reaction without a catalyst, the total mass of oxidation products and the proportion of MeOHS in oxidation products both increased after catalytic oxidation. This low-temperature oxidation technology can be used to upgrade asphaltenes, and thus can promote the exploitation and processing of heavy oil.
Enhanced oxygen vacancy (V
O
) has been designated as an effective strategy to prepare high-performance MnO
2
nanocatalysts for the oxidation of volatile organic compounds (VOC) for thereof ...unbalanced electronic structure, and rapid electron transfer which may even reduce the reaction temperature down to room temperature. Herein, the effects of the V
O
on the catalytic performance of nano-sized MnO
2
were discussed by classifying the V
O
into surface-anchored and bulk-involved ones. Currently used introducing and modulating methods for V
O
including elemental doping, energetic particle bombardment, atmosphere heat treatment, mechanical chemistry, and redox methods are detailly reviewed. Corresponding regulating mechanisms for V
O
are expounded. Commonly used characterization methods including ESR, XPS, HRTEM, and UV-vis are reviewed. Furtherly, the unveiled question which is highly expected to be answered on V
O
of MnO
2
nanocatalysts is proposed. The purpose of this review is to present the current status of research on MnO
2
nanoparticles and to provide researchers with basic research ideas.
Ceramic honeycomb monoliths were washcoated with cryptomelane-type manganese oxides and their catalytic performance was evaluated in the oxidation of ethyl acetate. The effect of a mixture of ethyl ...acetate with toluene and of the presence of water vapour was also assessed.
Different coating parameters, namely size of catalyst particles, number of immersions in the washcoating solution, presence of an initial coating with alumina, calcination temperature of this coating, as well as the amount of binding agent and ethanol in the washcoating solution were studied and optimized based on the catalytic activity of the structured catalyst. Small particles are required for a correct impregnation; however, since the smallest particles are less active, an intermediate size achieved the best catalytic results. Increasing the number of immersions over 3 did not significantly increase the catalytic activity of the structured catalyst. The presence of an initial coating with alumina and a binding agent (colloidal alumina) in the washcoating solution was found essential to increase the activity, whereas increasing the calcination temperature after the initial alumina coating above 500°C decreased the activity of the catalyst. The presence of ethanol in the washcoating solution did not significantly improve the activity of the structured catalyst.
The optimized structured catalyst presented high catalytic activity in the removal of ethyl acetate (90% conversion into CO
2
at 256°C) and high stability during 100 h of reaction. The addition of toluene or water vapour in the feed gas did not significantly affect the activity of the coated monolith.
Cryptomelane-type manganese oxides prepared by a solvent-free method were evaluated as catalysts for the oxidation of ethyl acetate, ethanol and toluene. The original catalyst (K-OMS-2) presented ...high catalytic activity for ethyl acetate and ethanol oxidation, achieving 90% conversion into CO
2
around 200°C for both pollutants. Toluene was much harder to oxidize, requiring a temperature near 270°C for the same conversion. The original catalyst was mechanically treated in a ball mill at different intensities, in order to decrease the particle size for subsequent impregnation onto structured supports, as small particle sizes are usually recommended. The catalytic activity of the materials decreases with the increase in the severity of this treatment, which is related to the decrease of the surface area of the catalysts, since the other properties (phase purity, thermal stability, surface oxygen, average oxidation state and reactivity of the oxygen species) are similar among the catalysts with different ball milling treatments. For comparison, a platinum-based catalyst (1%-Pt/Al
2
O
3
) was also tested, which exhibited a high activity for toluene, but much lower activities for the two other volatile organic compounds tested. A long-term experiment, using ethanol as model pollutant, showed that the cryptomelane catalyst was stable for more than 100 h.
The preparation of atomically dispersed catalysts with high metal loading remains a formidable challenge due to the high surface energy of single atoms. Here we prepared PtPd/TiO
2
catalysts ...possessing metal loading as high as 8.17 wt% by a new versatile method which based on metal oxide carriers with abundant oxygen defects. PtPd/TiO
2
catalysts consist of PtPd nanoparticles and atomically dispersed Pt and Pd atoms, and the content of PtPd nanoparticles is little. Pt
3
Pd
1
/TiO
2
-400 catalyst exhibited the highest catalytic activity in toluene oxidation, and with a 94.7% conversion at 110 °C. Kinetic investigation reveals that the toluene oxidation follows a typical Langmuir-Hinshelwood mechanism. Experimental research indicates that the superior catalytic activity could be attributed to a large number of metal atoms atomically dispersed on the surface of the catalyst. Pt and Pd atoms are close to each other, which produces the synergetic effect and thereby promotes toluene oxidation. This work provides a promising pathway to fabricate single atom catalysts with high loading.
•The surface of carbon nanotubes was covered uniformly by TiO2 layer.•The synergetic effect of CNT and TiO2 promotes the catalytic performance.•The catalyst prepared by NH3-coordination method had ...superior activity.•Pd species was easy to enrich on the surface of catalyst by NH3 coordination.
In this paper, a series of Pd-Ce/acid-treated carbon nanotube (TCNT)-TiO2 composite catalysts were designed and fabricated carefully for low temperature CO oxidation. After covering of TiO2 on the surface of CNT, the catalytic activity enhanced obviously because of the synergetic effect of CNT and TiO2. The composite material CNT-TiO2 was more suitable for the catalytic support than only TCNT or TiO2. The experimental conditions, such as the ratio of CNT/TiO2, the prepared method of Pd nanoparticles, the effect of the Ce element, etc., were investigated in detail. The final result showed that Pd-Ce/TCNT-TiO2 catalyst prepared by NH3 coordination impregnation method when TCNT:TiO2=12:88–24:76 had superior activity on low temperature CO oxidation. The high dispersion of Pd nanoparticles and enriched surface Pd species on the Pd-Ce/CNT-TiO2 catalyst prepared by NH3 coordination impregnation method was the two main reasons of obtaining higher catalytic performance. By adjusting the research conditions, the CO molecules could be complete oxidized at about 35°C, which was lower than many catalysts reported in the existed literature.
A series of rare earth zeolites Ln–ZSM-5 (Ln = La, Ce, Pr, Nd) were synthesized directly via a one-step hydrothermal method. The obtained zeolites were used as support and applied in low-temperature ...CO oxidation. The influence of various factors such as rare earth types, rare earth contents, particle sizes of molecular sieve, and silica alumina ratios, etc., on the catalytic activity of CO oxidation were investigated in detail. The results showed that low silica small size Ce–ZSM-5 (1 % Ce content) had the highest activity. The results also showed that Ce–ZSM-5 zeolite prepared by one-step direct synthesis was more suitable as catalytic support than ZSM-5 or Ce/ZSM-5 zeolite, prepared by impregnation of ZSM-5 with Ce.
