Higher CO Formation Research Articles

Isothermal reverse water gas shift chemical looping on La0.75Sr0.25Co(1−Y)FeYO3 perovskite-type oxides

The RWGS-CL is a two-step process for the conversion of CO2 to CO using a redox cycle of a parent metal oxide. Previously, this process was demonstrated using La0.75Sr0.25CoO3 perovskite, but this material required different oxidation and reduction temperatures. In this study, oxidation and reduction were achieved at the same temperature. La0.75Sr0.25Co(1−Y)FeYO3 (Y=0, 0.5, 0.75 and 1) perovskite-type oxides were synthesized by the Pechini method and were tested by X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR) and oxidation with carbon dioxide (CO2-TPO). Results demonstrated that the LaFeO3 (Y=1) sample showed structure stability when reduced at 550°C, the lowest CO formation onset temperature (450°C) and high selectivity toward CO. Five isothermal RWGS-CL cycles were performed at 550°C on the Y=1 sample. The stability of the crystalline structure throughout the cycles was demonstrated by XRD. CO formation rates increased during the first cycles and stabilized at the third cycle due to the increased accumulated amount of oxygen vacancies (δ) on the perovskite surface, which is consistent with the findings from the density functional theory studies that directly correlate the CO2 binding strength to the amount of oxygen vacancies. The high CO formation rates and the repeatability of the process make RWGS-CL a promising technology for CO2 conversion, if a renewable hydrogen source is available.

Oxygen Depletion and Formation of Toxic Gases following Sea Transportation of Logs and Wood Chips

Several recent accidents with fatal outcomes occurring during discharge of logs and wood chips from ships in Swedish ports indicate the need to better understand the atmospheric conditions in holds and connecting stairways. The principal aim of the present study was to assess the air levels of oxygen and toxic gases in confined spaces following sea transportation of logs and wood chips. The focus of the study was the conditions in the stairways, as this was the location of the reported accidents. Forty-one shipments of logs (pulpwood) and wood chips carried by 10 different ships were investigated before discharge in ports in northern Sweden. A full year was covered to accommodate variations due to seasonal temperature changes. The time from completion of loading to discharge was estimated to be 37–66 h (mean 46 h). Air samples were collected in the undisturbed air of altogether 76 stairways before the hatch covers were removed. The oxygen level was measured on-site by handheld direct-reading multi-gas monitors. On 16 of the shipments, air samples were additionally collected in Tedlar® bags for later analysis for carbon dioxide, carbon monoxide, and hydrocarbons by fourier transform infrared spectroscopy. The mean oxygen level was 10% (n = 76) but in 17% of the samples the oxygen level was 0%. The oxygen depletion was less pronounced during the cold season. The mean CO2 and CO levels were 7.5% (n = 26) and 46 p.p.m. (n = 28), respectively. More than 90% of the hydrocarbons were explained by monoterpenes, mainly α-pinene (mean 41 p.p.m., (n = 26). In conclusion, the measurements show that transport of logs and wood chips in confined spaces may result in rapid and severe oxygen depletion and CO2 formation. Thus, apparently harmless cargoes may create potentially life-threatening conditions. The oxygen depletion and CO2 formation are seemingly primarily caused by microbiological activity, in contrast to the oxidative processes with higher CO formation that predominate in cargoes of wood pellets. Improved technical and organizational measures are considered necessary to prevent future accidents. Recommendations given regarding safe entry procedures and technical preventive methods may also apply to other oxygen-depleting products.

Partial oxidation of ethanol over Pd/CeO 2 and Pd/Y 2O 3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H 2, CO 2 and acetaldehyde formation was favored on Pd/CeO 2, whereas CO production was facilitated over Pd/Y 2O 3 catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y 2O 3 catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH 4 and CO at high temperatures. On Pd/CeO 2 catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H 2, CH 4 and CO. The CO formed is further oxidized to CO 2, which seems to be promoted on Pd/CeO 2 catalyst.

Combustion characteristics of fatty acid methyl esters derived from recycled cooking oil

The goal of this study is to find out the exhaust emissions differences produced by different kinds of fatty acid methyl esters (FAME) derived from used cooking oils and animal fats, as well as the importance of the purification step in exhaust emissions production. A total of 120 L of waste vegetable oil and 30 L of waste frying oil were collected and converted into three batches of FAME. There were two batches of FAME produced from waste vegetable oil (B01 and B02), and one batch of FAME produced by mixing 2% of waste frying oil with waste vegetable oil (B03). The FAMEs used in this study had higher density, kinematic viscosity, and flash point, but a lower gross heating value, when compared to the premium diesel. The B01 engine produced higher CO formation and the diesel-fuelled engine produced higher CO than the B02 and B03 did for engine speeds higher than 1400 rpm. Most of the FAME fuels produced higher CO2 than the diesel fuel did. The FAME fuels emitted higher NOx and PM, but lower SO2, than the diesel fuel. CnH2n+2, diphenyl sulfone (C12H10O2S), and diethyl phthalate (C12H14O4) can be selected as the character index for the combustion of FAME.

Hydrogen production from methane decomposition over Ni/CeO 2 catalysts

The catalytic behavior of Ni/CeO 2 catalysts was investigated for methane decomposition at 773 K. Ni/CeO 2 catalysts prepared by impregnation and deposition–precipitation methods showed much higher hydrogen formation rates than that of Ni/CeO 2 catalyst prepared by coprecipitation method, which exhibited relatively higher CO formation rate. CH 4-TPSR measurements confirmed that CO formation is inevitable during methane decomposition, since the lattice oxygen of ceria could react with the deposited carbons. TEM observations further indicated that the morphologies as well as the reactivities of the deposited carbons are strongly dependent on the interaction degrees between Ni and ceria, which in turn explains the differences in the catalytic activity of the Ni/CeO 2 catalysts for methane decomposition. The Ni/CeO 2 catalyst prepared by coprecipitation method exhibited rather strong metal–support interaction probably through the formation of Ni–O–Ce solid solution, resulting in much lower hydrogen formation rate and relatively higher CO production.

Photocatalytic reduction of carbon dioxide using [ fac-Re(bpy)(CO) 3(4-Xpy)] + (Xpy = pyridine derivatives)

Photocatalytic reduction of CO 2 using [ fac-Re(bpy)(CO) 3(4-Xpy)] + [bpy = 2,2′-bipyridine, py = pyridine, X = tert-Bu, Me, H, MeCO, CN] in a triethanolamine (TEOA)–dimethylformamide (DMF) solution was examined. The quantum yields for CO formation were almost identical for each (0.03 to 0.04), except for the 4-CNpy complex. Irradiating the solutions caused ligand substitution of these complexes with solvent molecules to produce [ fac-Re(bpy)(CO) 3(TEOA)] + and [ fac-Re(bpy)(CO) 3(DMF)] +, followed by formation of the formate complex [ fac-Re(bpy)(CO) 3{OC(O)H}], which acts as the real catalyst for CO formation. On the other hand, the much higher CO formation ability observed for the 4-CNpy complex (quantum yield for CO formation = 0.13) was due to the participation of the cyano complex [ fac-Re(bpy)(CO) 3CN], which is converted from the 4-CNpy complex during irradiation. The photochemical substitution of the initial complexes with the solvent molecules is very rapid (quantum yields >1). This phenomenon is explained by a chain mechanism.

Hydrogenation of carbon dioxide over alumina supported Fe-K catalysts

The hydrogenation of CO2 has been studied over Fe/alumina and Fe-K/alumina catalysts. The addition of potassium increases the chemisorption ability of CO2 but decreases that of H2. The catalytic activity test at high pressure (20 atm) reveals that remarkably high activity and selectivity toward light olefins and C2+ hydrocarbons can be achieved with Fe-K/alumina catalysts containing high concentration of K (K/Fe molar ratio = 0.5, 1.0). In the reaction at atmospheric pressure, the highly K-promoted catalysts give much higher CO formation rate than the unpromoted catalyst. It is deduced that the remarkable catalytic properties in the presence of K are attributable to the increase in the ability of CO2 chemisorption and the enhanced activity for CO formation, which is the preceding step of C2+ hydrocarbon formation.

Base catalysis by alkali modified zeolites: III. Alkylation with methanol

Ion exchanged CsNaX and CsNaY, cesium acetate impregnated CsNaX ( CsAce CsNaX ) and CsNaY ( CsAce CsNaY ), and MgO have been reacted with isopropanol at 425 °C and atmospheric pressure to assess their acid/base properties at a temperature consistent with that used in the side chain alkylation of toluene with methanol. The results suggest that the ability of the catalysts tested here to promote a base mediated reaction follow the order of MgO > CsAce CsNaY > CsAce CsNaX ⋍ CsNaY > CsNaX . Selectivities to acetone measured at 4.73% conversion follow this order as well, ranging from 95.7% and 93.9% for MgO and CsAce CsNaY , respectively, to 17.6% for the CsNaX. Thus, these catalysts can be grouped into two categories: (i) catalysts which vary in acid/base properties yet possess identical topology (e.g., the zeolites) and (ii) catalysts which vary in topology yet have similar acid/base properties (e.g., MgO and CsAce CsNaY ). These catalysts were compared using the side chain alkylation of toluene, ethane, methane, and acetone with methanol. For the impregnated zeolites, similar toluene conversions were observed. Unlike the impregnated X zeolite, no formaldehyde (i.e., the alkylating agent) was observed in the product stream of the impregnated Y zeolite. Both MgO and CsAce CsNaY had similar methanol decomposition products; i.e., no formaldehyde and high CO formation, yet unlike CsAce CsNaY no toluene conversion was observed for MgO. No conversion of ethane or methane was observed for either impregnated zeolite at 425 °C. Attempts at higher temperatures (e.g., 465 °C) failed also. Acetone was alkylated to methyvinylketone and methylethylketone; however, the majority of the reacted acetone formed products which appear to result from acetone aldol condensations.