Search

MnO2/g-C3N4 nanocomposites were facilely synthesized by calcining the mixture of bulk g-C3N4 and MnO2 precursors. The effects of the morphology of MnO2 precursors and the mass ratio of MnO2 to g-C3...

The hydrogenation of CO2-derived carbonates to methanol is an alternative route for the indirect utilization of abundant C1 sources. Various Cu/SiO2 catalysts with different copper loading content prepared by using an ammonia evaporation hydrothermal method are implemented to evaluate the catalytic performance of ethylene carbonate (EC) hydrogenation to methanol and ethylene glycol (EG). The Cu loading content was identified to significantly affect the Cu nanoparticles (NPs) size and metal-support interaction. Highly dispersed Cu NPs restricted and embedded in copper phyllosilicate presented a smaller average particle size than the impregnated Cu/SiO2–IM catalyst. The xCu/SiO2 catalyst with ultrafine Cu NPs showed abundant Cu–O–Si interfaces, acidic sites, and coherent Cu0 and Cu+ species. The 5Cu/SiO2 catalyst achieved methanol yield of 76% and EG yield of 98% at EC conversion of 99%, and no obvious deactivation was observed after long-term operation. The superior catalytic performance of the 5Cu/SiO2 catalyst is attributed to the synergetic effect between the appropriate Cu0 surface area which provides sufficient active hydrogen, and the atomic ratio of Cu+ for the polarization and activation of carbon–oxygen bonds.

A plate-type anodic alumina support (γ-Al2O3/Fe–Cr–Ni alloy/γ-Al2O3) was used to prepare a series of Ru catalysts. The performance of these catalysts was investigated in the steam reforming of kerosene (SRK). Ethanol solution impregnation was used to enhance metal dispersion on the catalyst surface. The catalyst prepared by ethanol solution impregnation and dried at 120 °C (Ru/Al2O3-ED) gave a higher metal dispersion and more favorable activity and durability than that prepared in aqueous solution. However, owing to shrinking caused by the oxidation of ruthenium species, high temperature calcination in air after impregnation greatly decreased the metal dispersion on the catalyst surface, regardless of the impregnation solution type. In contrast to calcination in air, high temperature N2 treatment could decompose the reducible ruthenium species on the Ru/Al2O3-ED completely. This indicates that H2 pre-reduction is not an essential procedure for the SRK reactions over this catalyst. The experimental results also confirm this hypothesis. The effect of Ce addition was also investigated and was found to enhance significantly the catalyst tolerance to carbon deposition thereby improving the SRK durability of Ru/Al2O3-ED under a high space velocity. In addition, owing to the high electrical resistance of the Fe–Cr–Ni alloy, the anodic alumina catalyst itself can be used as a heater, when an electrical current is applied along the alloy layer. Under an electrical-heating pattern, the SRK reaction system reached stability within 15 min, offering a strong possibility for shortening the start-up time of conventional reformers from 1 to 2 h to a few minutes.

An anodic alumina supported silver catalyst (1.7 Ag/Al2O3) was synthesized to investigate the selective catalytic reduction (SCR) of NO under an electrically heating pattern. It was found that less than 1 min was required to heat the catalyst from room temperature to 450°C. Comparing with a common furnace heating pattern, similar de-NOx activity was achieved. According to the electrically heating tests, the NOx conversion of 1.7 Ag/Al2O3 remained above 80% for 15 h at 450°C (F/W = 65000 mL/(g · h)), which proved that it was commendable to apply this type of catalyst to C3H6-SCR of NO. Additionally, the promotional effect of hydrogen additive is also discussed under the electrically heating pattern. In the presence of 2000 ppm of hydrogen, the 1.7 Ag/Al2O3 reached 80% NOx conversion within a few seconds at 300°C, while the activity was very low at 300°C without hydrogen; such a high conversion was maintained for 15 h.

Two plate-type anodic alumina supported Ru catalysts, Ru/Al and Ru/Ce–Al, has been employed to investigate activities in the kerosene steam reforming reaction. H2 pre-reduction during the kerosene steam reforming was found not an essential procedure, in terms of activity and stability. In addition, the Ru/Ce–Al catalyst was more stable than Ru/Al without pre-reduction in the accelerated life test. In the 20 times of DSS operation over Ru/Ce–Al, no remarkable decline in kerosene conversion was observed, indicating that Ru/Ce–Al was tolerable to multiple cycles under such severe conditions without obvious deterioration. Under an electric heating pattern, the performance of catalyst Ru/Ce–Al was investigated. It showed that 100% of kerosene conversion would be obtained in just 15 min over the Ru/Ce–Al catalyst when the kerosene was introduced into the reactor. It also presented excellent stability during test and DSS operation, which indicates more promising lifetime for the Ru/Ce–Al catalyst in the wall-type reformer.

Plate-type metal monolithic anodic alumina supported Ru catalysts prepared by impregnation method has been employed for the kerosene steam reforming. The characteristics of the catalysts were analyzed by ICP, BET, TG and FESEM. We found that although plate-type Ru/Al2O3 catalyst displayed favorable activity in the long-term stability test, coke deposition resistance should be further improved. In order to inhibit the coking during the reforming reaction, ceria was added to Al2O3 support to synthesize Ru/Ceria-Al2O3 catalysts. The results showed that ceria addition to the Ru/Al2O3 catalyst enhanced the catalyst stability, resulting from the lower content of coke formation on the catalyst surface. Furthermore, it showed that the content of ceria had a greater impact on the content of coke formation on the catalyst surface. If more ceria were contained in Ru/Ceria-Al2O3 catalyst, less coke would be formed over the catalyst surface during the reaction.

A series of anodic alumina supported silver/titanium catalysts (Ag/Ti/Al2O3) were synthesized to investigate the effect of Ti on the selective catalytic reduction of NO with propene. In the low temperature region, the SCR activity was greatly enhanced on Ag/Ti/Al2O3 compared to Ag/Al2O3, and this promotion became more significant with increasing Ti loading. Adding Ti to an anodic alumina support did not cause obvious improvement of activity, indicating that the presence of Ti acted as a catalytic promoter of Ag, but did not directly participate in the SCR reaction. The result of NOx-TPD in flowing He showed that no obvious difference in the desorption performance of ads-NOx species was found between Ag/Al2O3 and Ag/Ti/Al2O3. However, in flowing O2/C3H6/He the desorption peak of nitrate species was decreased by about 50°C when Ti was present. The promoted partial oxidation of the reducing agent was believed to be a main reason. The result of H2-TPR suggested that besides Ag+ ion and metallic Ag another type of silver existed in Ag/Ti/Al2O3, possibly a moderately agglomerated Agnδ+ cluster. Additionally, in comparison with the SO2-aged Ag/Al2O3 catalyst, the SO2-aged Ag/Ti/Al2O3 catalyst provided a favorable tolerance to SO2 poisoning, and led to higher activity. A relatively lower SO2 adsorption amount and a faster reduction rate of sulfate species by propene were considered to be a reasonable interpretation.

A novel metal monolithic anodic γ-Al2O3 support was prepared by anodization using a clad aluminum plate. The catalytic combustion of methane on Pt/Al2O3/Alloy, Pd/Al2O3/Alloy and Pd–Pt/Al2O3/Alloy catalysts prepared by the impregnation method was studied. The catalysts were characterized by ICP, BET, and temperature-programmed oxidation (TPO). The results showed that at low temperatures ( 700°C), Pd–Pt/Al2O3/Alloy showed the best activity among these three catalysts, whereas the activity of Pd/Al2O3/Alloy decreased gradually. Therefore, it was concluded that the co-existence of Pd and Pt in the Al2O3/Alloy support in Pd–Pt/Al2O3/Alloy made its activity the best among that of all the catalysts studied over the entire temperature range (400–800°C) considered for methane combustion.

An anodic alumina supported 17.9 wt% Ni catalyst shows an excellent catalytic performance during steam reforming of methane at 700°C under W/F = 6.33 × 10–3 g-cat·h/L, even when compared with some commercial Ni and Ru reforming catalysts. This is considered to be the result of the existence of an interfacial NiAl2O4 layer, which could anchor the top metallic nickel particles to prevent them from reacting with the alumina support and sintering, thereby, effectively suppressing carbon deposition. Nevertheless, for the industrialization of anodic nickel catalysts, some effort should be made to alleviate the deterioration of anodic supports, because when subjected to a higher W/F as 1.27 × 10–3 g-cat·h/L, the catalyst shows irreversible deactivation, and little improvement is seen by increasing nickel spinel content and metal loading or modifying the impregnation solution pH.

A 17.9 wt.% Ni/Al 2 O 3 /alloy catalyst with porous anodic alumina support was subjected to steam reforming of methane after 700 °C steam purging and no reactivity was shown because of surface oxidation of sintered Ni particles. When 0.05 wt.% Ru doped on this catalyst, it exhibited self-activation and self-regenerative activity, resulted from the hydrogen spillover over Ru and/or Ru–Ni alloy. Moreover, a 97% CH 4 conversion was kept for 20 h over the catalyst under electrical heating pattern.