10 Search Results

Towards the goal of integrating CO₂ capture using aqueous ammonia with its utilization for algae cultivation, Scenedesmus acutus (UTEX B72) was grown in 1100 L open raceway ponds using CO₂ and NH₃ supplied from gas cylinders. CO₂/NH₃ mole ratios of 7 and 10 were employed, the gas mixture acting as a surrogate for the output from a CO₂ scrubbing system using aqueous ammonia. Compared to Scenedesmus acutus grown in open ponds using gaseous CO₂ and NaNO₃ as the N-source, the ponds supplied with gaseous CO₂ and NH₃ displayed higher productivity at both CO₂/NH₃ ratios, with the higher ratio providing themore » best growth. Depending on the culturing conditions and CO₂/NH₃ ratio, CO₂ utilization ranged up to 15.8% and NH₃ utilization to 23.0%. These rather low values reflect the fact the high CO₂/NH₃ feed rate used, resulting in a substantial release of NH₃ from the ORPs (~45%). Finally, these findings demonstrate the suitability of gaseous NH₃ as a N-source for microalgae cultivation, while highlighting the need for a control strategy that closely balances the CO₂/NH₃ supply with the algae growth rate. The produced algae biomass possessed a high protein and low ash content, rendering it particularly suitable for use as a bioplastic feedstock.« less

Integrating CO₂ scrubbing from flue gas with its utilization in algae cultivation represents a potential means of lowering the cost of CO₂ capture. Towards this goal, this study sought to assess the feasibility of using gaseous a CO₂/NH₃ stream, derived from CO₂ capture using aqueous ammonia, as a C- and N-source for algae cultivation. Scenedesmus acutus was cultured in 800 mL photobioreactors using gaseous CO₂/NH₃ in mole ratios varying from 7 to 18. Excellent growth of Scenedesmus acutus was observed, the average growth rate for CO₂/NH₃ = 10 of 0.171 ± 0.015 g/L·day exceeding that obtained using 1% CO₂/N₂ andmore » urea as the N-source (0.099 ± 0.28 g/L·day). Under optimal growth conditions (CO₂/NH₃ mole ratio of 10), CO₂ utilization ranged from 57% to 72%, while the NH₃ utilization was >90%. The CO₂/NH₃ feed rate was also found to exert a significant effect on algae productivity, excessive feed rates leading to accumulation of NH₃ in the culture at concentrations that were toxic to the algae. Consequently, to avoid the toxic effects of high NH₃ concentrations (>2.0 mM), it proved necessary to balance the NH₃ supply with the algae growth rate so that excessive NH₃ accumulation was prevented. This indicates that for practical applications, a CO₂/NH₃ feed control strategy would be required that takes into account the ammonium ion concentration in solution and the pH so as to avoid significant concentrations of free NH₃. Furthermore, analysis of the harvested biomass revealed a high protein (≥ 47 wt%) and a low ash content (< 3.6 wt%), suggesting it would be well suited for use as animal feed or as a feedstock for the production of bioplastics.« less

For this study, three Pd/H-CHA samples were prepared containing 53.0%, 10.8% and 6.5% paired Al sites at near fixed Si/Al ratio and similar Pd loading. According to H₂ temperature-programmed reduction, Pd was present almost exclusively as isolated cations in the two samples containing the higher concentrations of paired Al sites, whereas in the other sample PdO was also present. Simulated lean cold start tests on the fresh samples conducted in a microflow reactor showed that the sample containing PdO stored the lowest amount of NOx. When tested with CO/H₂, the sample containing 53.0% paired Al sites showed significantly better storagemore » capacity than the other samples and deactivated less rapidly upon sequential tests. Experiments using lean gasoline engine exhaust revealed similar trends. This study showed that a high concentration of paired Al sites in Pd/H-CHA is beneficial for NOx storage capacity, thermal durability, and minimizing deactivation in the presence of CO/H₂.« less

The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al₂O₃ catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H₂-chemisorption, NH₃ temperature programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X ray diffraction (XRD). The catalysts were tested in a 1 L continuously stirred tank reactor (CSTR) at 220 °C, 2.2 MPa, H₂/CO = 2.1 and 20–55% CO conversion. Addition of 1% of Cd or In enhanced the reduction degree of 15%Co/Al₂O₃ by ~20%, while addition of 1%more » Sn slightly hindered it. All three additives adversely impacted Co dispersion by 22–32% by increasing apparent Co cluster size based on the H₂-chemisorption measurements. However, the decreased Co active site density resulting from the additives did not result in a corresponding activity loss; instead, the additives decreased the activity of the Co catalysts to a much greater extent than expected, i.e., 82–93%. The additional detrimental effect on catalyst activity likely indicates that the Cd, In and Sn additives migrated to and covered active sites during reaction and/or provided an electronic effect. XANES results showed that oxides of the additives were present during the reaction, but that a fraction of metal was also likely present based on the TPR and reaction testing results. This is in contrast to typical promoters that become metallic at or below ~350 °C, such as noble metal promoters (e.g., Pt, Ru) and Group 11 promoters (e.g., Ag, Au) on Co catalysts in earlier studies. In the current work, all three additives remarkably increased CH₄ and CO₂ selectivities and decreased C₅₊ selectivity, with the Sn and In additives having a greater effect. Interestingly, the Cd, In, or Sn additives were found to influence hydrogenation and isomerization activities. At a similar conversion level (i.e., in the range of 40–50%), the additives significantly increased 2-C₄ olefin content from 3.8 to 10.6% and n-C₄ paraffin from 50 to 61% accompanied by decreases in 1-C₄ olefin content from 48 to 30%. The Sn contributed the greatest impact on the secondary reactions of 1-olefins, followed by the In and Cd. NH₃-TPD results suggest enhanced acid sites on cobalt catalysts resulting from the additives, which likely explains the change in selectivities for the different catalysts.« less

Pd-promoted ZrO₂ and WO₃-ZrO₂ (W-Zr) were investigated for low temperature NOx adsorption and release. Pd-promoted W-Zr exhibited high NOx storage efficiency at short storage times, subsequently releasing ~95% of the stored NOx upon thermal ramping to 350 °C. DRIFTS studies demonstrated that Pd increased nitrate formation relative to nitrite during NOx storage on both Pd-Zr and Pd-W-Zr. Moreover, Pd sites on Pd-W-Zr played a major role in NOx storage, the ad-species being readily removed by 350 °C. From NO- and CO-DRIFTS data, it is inferred that Pd on the acidic W-Zr support was present as mainly cationic species, and wasmore » therefore able to adsorb NO, whereas on ZrO₂ Pd was not able to directly store NOx. Co-feeding CO with NO resulted in increased NOx storage capacity for Pd-W-Zr, which on the basis of DRIFTS measurements is attributed to the formation of Pd²⁺(CO)(NO) complexes.« less