Unwanted CO Research Articles

A novel alkylation process of benzene with CO2 and H2 over bifunctional ZnxCeyZrzO/Z5 catalyst

Alkylation of benzene using CO2 and H2 to toluene and xylene (TX) can not only give value-added chemical products but also alleviate the greenhouse effect. The key to achieving this goal is to develop a highly efficient catalyst. Herein, a class of bifunctional catalysts containing series of ZnxCeyZrzO metal oxide and HZSM-5 was prepared and studied for the catalytic properties. Higher CO2 conversion and alkylation utilization were achieved using the ZnxCeyO coupling with HZSM-5 compared to its counterpart ZnO and CeO2, revealing synergy between the ZnO and CeO2. More strikingly, the ZnxCeyZrzO, synthesized by insertion of Zirconia (Zr) atoms into CeO2, can not only improve the concentration of oxygen vacancy but also facilitate CO2 adsorption. After coupling with HZSM-5, the alkylation utilization of CO2 was significantly improved and the unwanted CO selectivity was obviously reduced by hindering the RWGS reaction. The optimal bifunctional catalyst Zn3Ce1Zr3O/Z5 showed alkylation utilization of 24%, unwanted CO selectivity of only 64% and the TX selectivity as high as 82%. In situ DRIFTS results confirmed that the methanol generated on the ZnxCeyZrzO metal oxide via the formate-methoxy intermediates mechanism was rapidly alkylated on HZSM-5 with benzene to produce TX.

Selectivity-induced conversion model explaining the coke-catalysed O2-mediated styrene synthesis over wide-pore aluminas

Explaining the conversion and selectivity of a heterogeneous catalyst is often done separately. The general rule is that with high temperatures conversion increases but the catalyst becomes less selective to the desired product, as other pathways to side products are activated. However, this study shows that conversion and selectivity can be correlated. Ethylbenzene (EB) can be converted into styrene under oxidative dehydrogenation conditions. This process is catalysed by the coke formed on an acidic solid material (alumina in this study) at the beginning of the reaction. The process also produces unwanted CO and CO2 (denoted as COx). In a previous study, the alumina calcination temperature influenced the coke selectivity; it increased the styrene selectivity. The EB conversion was also enhanced and it was explained in qualitative terms. In this work, we developed a quantitative model explaining the changes in EB conversion related to the selectivity. The model was obtained by setting an O2 mass balance and showed to explain the experimental reaction data well. The enhanced EB conversion, observed in the alumina series, was explained by the fact that the coke becomes less selective to the unwanted COx, and more to styrene. The COx-forming reactions consume more O2 than the styrene reaction, and have a highly negative impact on the EB conversion. The study provides evidence for the difficulty in achieving a high EB conversion under ODH conditions when COx is formed. For instance, to achieve an EB conversion above 80%, the selectivity to COx should be below 4% at O2/EB of 0.6 (mole) for a typical alumina catalyst. The model proves the link between conversion and selectivity and, secondly, the demanding conditions to achieve a high EB conversion for this reaction. To the best of our knowledge, this is the first example showing a quantitative model relating selectivity and conversion for a heterogeneously catalysed reaction.

Two-in-One Catalyst Turns Carbon Dioxide in Base Chemicals

Cascading chemical reactions can be realized when the local structure and composition of two catalytically active phases are fine-tuned and combined in one material. In this issue of Chem, Fan et al. report an innovative approach for the conversion of carbon dioxide into light olefins with a metal oxide-zeolite tandem catalyst.

Metal organic framework-derived 3D nanostructured cobalt oxide as an effective catalyst for soot oxidation

While Co3O4 represents one of the most promising catalysts for soot oxidation, conventional Co3O4 nanoparticles (NPs) tend to aggregate, losing their activities. Herein, an alternative approach is proposed for preparing three-dimensional nanostructured Co3O4 (NSCo) using the hierarchically-structured Co-based Metal Organic Frameworks as a precursor. Specifically, ZIF-67 is chosen as the precursor as ZIF-67 can be conveniently synthesized with high yields and it can be easily converted to NSCo via calcination. The resulting NSCo exhibits a unique morphology which enables NSCo to possess more porosities and surface areas than the typical Co3O4 NPs. Consequently, NSCo shows a much higher catalytic activity than the typical Co3O4 NPs for soot oxidation because of superior textural properties of NSCo. Besides, when the soot oxidation by the typical Co3O4 NPs produced a significant amount of unwanted CO, soot can be completely combusted into CO2 using NSCo. In comparison with other reported Co-related catalysts, NSCo also achieves a higher soot oxidation efficiency (100% conversion) at lower temperatures with Tig of 331 °C. NSCo can be reused over many continuous cycles and still retains its catalytic activities. These features validate that NSCo is an easy-to-prepare 3D nanostructured Co3O4 catalyst, which possesses advantageous capabilities for soot oxidation at lower temperatures.

Physico-chemical elimination of unwanted CO2, H2S and H2O fractions from biomethane

It was possible to increase the biomethane content of raw biogas by removing CO2, H2S and water (H2O) by a physico-chemical method.

Dehydrogenation of Formic Acid over a Homogeneous Ru-TPPTS Catalyst: Unwanted CO Production and Its Successful Removal by PROX

Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been reported to be very selective towards FA dehydrogenation (resulting in H2 and CO2), a side-production of CO and H2O (FA dehydration) should also be considered, because most PEM hydrogen fuel cells are poisoned by CO. In this research, a highly active aqueous catalytic system containing Ru(III) chloride and meta-trisulfonated triphenylphosphine (mTPPTS) as a ligand was applied for FA dehydrogenation in a continuous mode. CO concentration (8–70 ppm) in the resulting H2 + CO2 gas stream was measured using a wide range of reactor operating conditions. The CO concentration was found to be independent on the reactor temperature but increased with increasing FA feed. It was concluded that unwanted CO concentration in the H2 + CO2 gas stream was dependent on the current FA concentration in the reactor which was in turn dependent on the reaction design. Next, preferential oxidation (PROX) on a Pt/Al2O3 catalyst was applied to remove CO traces from the H2 + CO2 stream. It was demonstrated that CO concentration in the stream could be reduced to a level tolerable for PEM fuel cells (~3 ppm).

Performance of Cu-Zn-Al-Zr catalyst prepared by ultrasonic spray precipitation technique in the synthesis of methanol via CO2 hydrogenation

The effects of the newly improvised catalyst preparation technique, namely ultrasonic spray precipitation (USP), on the physicochemical properties as well as the catalytic performance of Cu-Zn-Al-Zr catalyst in CO2 hydrogenation reaction were studied. Spraying technique is advantageous in generating micro-droplets of catalyst precursors by providing high surface area contact during precipitation, while the incorporation of an ultrasonic irradiation can physically alter the surface morphology of the catalyst. In this study, Cu-Zn-Al-Zr catalysts were prepared using both USP and conventional precipitation (CP) techniques for comparison purposes. Structural analysis showed that USP technique dictated the formation of finer Cu crystallites with better particle uniformity. Meanwhile, TPR results revealed a good interaction between different elements in the catalyst with the formation of single form of oxide species. In terms of reactivity, USP-prepared catalyst outperformed CP catalyst for CO2 conversion by 20.9% and also improved methanol selectivity and yield by 2.7 and 27%, respectively, while reducing noticeably the unwanted CO. It is believed that the improved surface basicity of USP catalyst, which has a great influence on reaction pathways of intermediate species, contributed significantly to the enhanced catalytic performance, and hence justifying the superiority of this new preparation technique over the conventional ones.

Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts.

The exothermic oxidative dehydrogenation of propane reaction to generate propene has the potential to be a game-changing technology in the chemical industry. However, even after decades of research, selectivity to propene remains too low to be commercially attractive because of overoxidation of propene to thermodynamically favored CO2 Here, we report that hexagonal boron nitride and boron nitride nanotubes exhibit unique and hitherto unanticipated catalytic properties, resulting in great selectivity to olefins. As an example, at 14% propane conversion, we obtain selectivity of 79% propene and 12% ethene, another desired alkene. Based on catalytic experiments, spectroscopic insights, and ab initio modeling, we put forward a mechanistic hypothesis in which oxygen-terminated armchair boron nitride edges are proposed to be the catalytic active sites.

Steering of methanol reforming selectivity by zirconia–copper interaction

“Inverse” (ZrO2/ZrOxHy on Cu) and “real” (Cu nanoparticles on ZrO2) ultra-high-vacuum/ambient pressure model catalyst studies were performed using methanol steam reforming as a test reaction. The catalytic profile was correlated with structural and spectroscopic analysis using X-ray photoelectron and Auger electron spectroscopy and high-resolution electron-energy-loss spectroscopy. Access to water-activation-dependent pathways is achieved by special Cu/ZrOxHy phase boundary or interfacial sites formed during reaction, which were studied with respect to surface coverage, island size, and chemical state of Cu/Zr metal/oxide species. In the “real” model system, particle size effects increasing the amount of unwanted CO were observed beyond interfacial selectivity-steering effects. Oxidation of Zr0 to Zr+4 during reaction forms the most efficient phase boundary with respect to redox-active sites. Ability for reversible hydroxylation of Zr and submonolayer Zr coverage for maximum ZrOxHy/Cu phase boundary dimensions are the most critical parameters in catalyst preparation.

Shape and size of red blood cells from the Pygoscelid penguins of Antarctica using atomic force microscopy

Antarctic biodiversity is evolutionarily com- plex, reXecting the extreme ambient conditions. Therefore, Antarctic organisms exhibit sophisticated adaptations in all organization levels, including organs, tissues, and cells. Since red blood cells (RBCs) travel through the vertebrates blood delivering O2 to all tissues and organs and purging the unwanted CO 2 , they represent an interesting model to investigate biological adaptations. We have used atomic force microscopy (AFM) to compare the shape and size of RBCs of the Pygoscelid penguins. A total of 18 landmarks were measured in AFM images. When analyzed individu- ally, the parameters were not capable of discriminating the RBCs of each species. However, the simultaneous use of multiple parameters discriminated (74%) among the RBCs. In addition, the use of RBC measurements was suYcient to hierarchically cluster the species in accordance to other common and reliable phylogenetic strategies. In light of these results, the use of RBC characters could eVectively beneWt taxonomic inferences.

Novel methanol steam reforming activity and selectivity of pure In2O3

Pure In 2 O 3 thin film and In 2 O 3 powder catalysts were found to be structurally stable and highly active and CO 2 -selective in methanol steam reforming between 450 and 673 K. No catalytic activity in both routes of the water–gas shift reaction as tested in the same temperature region where the catalysts exhibit high reforming activity and selectivity, could be observed. Electron-microscopy suitable In 2 O 3 thin films prepared by thermal deposition of In 2 O 3 powder in 10 −2 Pa O 2 at 600 K and, for comparison, a commercial polycrystalline In 2 O 3 powder catalyst were tested in methanol steam reforming and in both routes of the water–gas shift reaction as a function of reaction temperature. The effect of oxidative (1 bar O 2 , 373–673 K, 1 h) and reductive (1 bar H 2 , 373–673 K, 1 h) catalyst pre-treatments was assessed. The resulting structural and morphological changes occurring during catalyst activation and catalytic reaction were monitored by (high-resolution) transmission electron microscopy, scanning electron microscopy and surface area measurements by N 2 adsorption according to BET. Both the In 2 O 3 thin film and the powder sample were observed to be structurally stable under typical catalyst pre-treatments in oxygen and hydrogen at temperatures T ≤ 673 K and T < 673 K, respectively, as well as under typical methanol steam reforming conditions at temperatures T ≤ 680 K. No pronounced catalyst sintering was observed below 673 K. Both In 2 O 3 samples were found to be highly active and selective toward CO 2 in methanol steam reforming over a broad temperature range (450 < T < 673 K). Selectivities of >95% toward CO 2 were usually observed, with at maximum 5% or less CO formed. No dependence of selectivity on either reaction temperature or oxidative/reductive pre-treatment was observed. No catalytic activity in both routes of the water–gas shift reaction as tested in the same temperature region where the catalysts exhibit high reforming activity and selectivity, could be observed. Therefore In 2 O 3 based catalysts offer a broad range of temperature not influenced by unwanted CO formation via the inverse water–gas shift process.

Design and performance of a measuring system for CO 2 exchange of a greenhouse crop at different light levels

At low light levels measured and in a dynamic greenhouse climate, crop photosynthesis does not match prediction by photosynthesis models. In order to address this problem, a greenhouse scale crop photosynthesis measuring system was designed to generate data that can be used to validate crop photosynthesis models. The system is based on net CO 2 exchange of a crop and was tested with a full scale cut chrysanthemum crop including the canopy bed structure. The system was used to measure crop photosynthesis at different CO 2 concentration levels (350 and 970 μmol mol −1 ), different temperatures, various low-photosynthetic photon-flux densities (PPFD; 85 and 160 μmol m −2 s −1 ) and natural light conditions (0–600 μmol m −2 s −1 ). The system consisted of two identical closed greenhouses (44 m 2 floor area each) that were sealed against air infiltration and tested on the occurrence of air leakage and unwanted CO 2 sources with the help of tracer gases. The CO 2 was supplied by computer-controlled flow proportionally to the difference between set point and measured concentration. An error analysis was applied successfully to find the required system characteristics needed to meet the requirement of a maximum system error of 5% for net CO 2 exchange measurements even at low photosynthesis levels. The description of the arrangement, calibration and testing of this system supports the design process of accurate large-scale crop photosynthesis measuring systems for use in crop photosynthesis research.