Combustion of Volatile Organic Compounds at Trace Concentration Levels in Zeolite-Coated Microreactors

Non-thermal plasma synthesis of supported Cu-Mn-Ce mixed oxide catalyst towards highly improved catalytic performance for volatile organic compound oxidation

Compared with that of the transition metal mixed oxide pellet catalyst, the catalytic activity of the supported mixed oxide catalyst was significantly reduced, which was limited in practical industrial applications. In this work, supported Cu-Mn-Ce mixed oxide catalysts were prepared by non-thermal plasma. Catalyst characterization result demonstrated that plasma treatment could promote the proportion of oxygen vacancy and enhance the adsorptive strength of VOCs on the surface of catalyst. Meanwhile, plasma treatment process exerted a slight influence on the pore structure and morphological property of the catalyst. Consequently, CMC/SiO₂-P exhibited much higher catalytic activity than CMC/SiO₂ prepared by the incipient wetness impregnation method for the catalytic oxidation of toluene and n-hexane. Among the catalysts prepared, the 15%CMC/SiO₂-P catalyst even exhibited a high catalytic activity comparable to that of the supported noble metal catalyst for the oxidation of the inert hexane. The T₉₈ of toluene and n-hexane over 15%CMC/SiO₂-P was 260 and 280°C under the conditions of VOC concentration at 1000 ppm and WHSV at 20,000 mL·g^-1·h^-1, respectively. This work provided a novel method for the preparation of the supported transition metal mixed oxide catalyst.

Coke Deposition and Structural Changes of Pellet V2O5/NaY-SiO2 in Air Regeneration: The Effects of Temperature on Regeneration

V2O5/NaY-SiO2 adsorbents were prepared by soaking up vanadium oxalate precursors into pellet NaY-SiO2. The NaY-SiO2 supports were prepared from NaY-SiO2 dough followed by extrusion and calcination at 450 °C. Ethanol was used as a model adsorbate to test the performance of the adsorbents. The regeneration efficacy, defined as the ratio of the adsorption capacity of a regenerated adsorbent to that of the fresh adsorbent, was investigated through the dynamics of fixed-bed adsorption (breakthrough curve). TPO, DSC, and FT-IR were used to characterize carbonaceous species on the adsorbents; meanwhile, synchrotron XRPD, XAS, and the N2 isotherm were used to characterize the zeolite, vanadia structure, and surface area, respectively. The results indicated that in low temperature (300 °C) regeneration, adsorption sites covered by alkylated aromatic coke formed during regeneration, causing adsorbent deactivation. In contrast, during regeneration at a high temperature (450 °C), the deactivation was caused by the destruction of the NaY framework concomitant with channel blockage, as suggested by the BET surface area combined with Rietvelt XRPD refinement results. In addition, the appearance of V-O-V contribution in the EXAFS spectra indicated the aggregation of isolated VO4, which led to a decrease in the combustion rate of the carbonaceous species deposited on the adsorbents. For regeneration at 350 and 400 °C, only trace coke formation and minor structural destruction were observed. Long-term life tests indicated that regeneration at 400 °C presents a higher maintenance of stability.

Microwave-Assisted Catalytic Combustion for the Efficient Continuous Cleaning of VOC-Containing Air Streams

A microwave-heated adsorbent-reactor system has been used for the continuous cleaning of air streams containing n-hexane at low concentrations. Both, a single catalytic bed (PtY zeolite) and a double (adsorptive DAY zeolite + catalytic PtY zeolite) fixed-bed reactor configurations were studied under dry and humid conditions. The zeolites were selectively heated by short periodic microwave pulses that caused the desorption of n-hexane and its subsequent catalytic combustion. The double bed configuration was attractive because it allowed nearly the same performance with only half of the catalyst load. The operation was especially efficient under realistic humid gas conditions that favored more intense microwave absorption, producing a faster heating of the adsorptive and catalytic beds. Under these conditions, continuous gas cleaning could be achieved with short (3 min, 30 W) microwave heating pulses every 5 min.

Towards the continuous production of Pt-based heterogeneous catalysts using microfluidic systems

The continuous production of Pt-based heterogeneous catalysts based on ultra-small (<2 nm) noble metal nanoparticles deposited on mesoporous ordered silica and their catalytic activity in VOC abatement are here reported. Microfluidic reactors can be used not only to enable the fast and controlled production of ultra-small Pt nanoparticles (NPs), but also alloyed NPs including PtPd, PtRu and PtRh can be formed in short residence times (between 60 s and 5 min). A novel continuous and homogeneous loading of these catalytic NPs on SBA-15 used as a mesoporous support is also here reported. This procedure eases the NP loading and minimizes washing post-treatments. A 12-fold decrease in the synthesis time was obtained when using this microfluidic reactor compared to the traditional batch production of Pt NPs. Microflow and batch type reactors yielded a Pt precursor conversion to generate Pt NPs with a 90% and 85% yield, respectively. Under the same conditions, the productivity of the microfluidic system (27 mg Pt NPs per h) was twice the one achieved in the conventional batch type reactor. The catalytic performance of the supported catalysts separately prepared by microfluidics and by conventional impregnation under the same conditions and with the same noble metal loading was also compared in the n-hexane abatement as a model of VOCs. Both catalysts were active in the VOC oxidation reaction but a 95% reduction in the catalyst synthesis time was obtained when using the catalysts produced in the microfluidic platform. For this reaction a long-term activity test was successfully carried out at 175 °C during 30 h on stream using the heterogeneous catalyst prepared by using the flow reactor.

Total oxidation of isopropanol over manganese oxide modified ZSM-5 zeolite membrane catalysts

Manganese oxide modified ZSM-5 membrane catalysts were prepared for the catalytic combustion of a volatile organic compound (isopropanol) over a zeolite membrane reactor.