Ceria-zirconia oxide high temperature desulfurization sorbent

High temperature desulfurization of highly reducing coal-derived gases using ceria and ceria-zirconia sorbents is the primary object of this dissertation research. If H2S concentration is reduced to less than 1 ppmv the product gas may be used with fuel cells and downstream catalytic process. CeO2 is reduced to a non-stoichiometric oxide, which is superior to CeO2 in removing H2S. Moreover, ZrO2 addition to CeO2 to form a solid solution, Ce1-xZrxO2, increases the reducibility of CeO2. This should also result in improved desulfurization performance. Pure CeO2 and sorbents, both commercially available and prepared at LSU, were tested. XRD analysis indicated that all sorbents containing ceria and zirconia formed a single phase. TGA analysis showed that overall reducibility of Ce1-xZrxO2 sorbents was better than pure CeO2. BET surface area measurements were also made to further characterize the sorbents. In the early stages of this research, commercially available sorbents were used for sulfidation tests. Experimental results were very promising. However, these commercially available sorbents were obtained from different sources and the differences in chemical and structural properties overwhelmed the possible effect of ZrO2 addition. Experimental results using LSU sorbents prepared using a coprecipitation method also produced favorable desulfurization results. H2S concentration in the product gas was reduced to less than 1 ppmv during the prebreakthrough phase of sulfidation tests with feed rates corresponding to about 3.8 second reactor residence time at temperatures in the range of 600 to 750oC. Addition of ZrO2 did not result in significant reduction of the H2S concentration during prebreakthrough, but did increase the duration of the prebreakthrough period. Addition of CO2, an oxygen source, to the feed gas decreased the prebreakthrough duration, but did not alter the sorbent’s ability to achieve sub-ppmv H2S concentrations level during prebreakthrough

High Efficiency Desulfurization of Synthesis Gas Annual Report

Mixed metal oxides containing CeO{sub 2} and ZrO{sub 2} are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv or less H{sub 2}S. The research is justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeO{sub n} (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and should have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} were prepared. XRD showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Unfortunately, the quantity of CeO{sub 2}-ZrO{sub 2} that could be prepared electrochemically was too small to permit full testing in our desulfurization reactor. Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that may be exposed to low concentrations of H{sub 2}S are constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time is determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H{sub 2}S concentrations ({approx}< 10 ppmv) and a thermal conductivity detector (TCD) for higher concentrations of H{sub 2}S. Larger quantities of CeO{sub 2}-ZrO{sub 2} mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, have been obtained. Characterization and desulfurization testing of these sorbents began in year 02 and is continuing. To properly evaluate the effect of ZrO{sub 2} addition on desulfurization capability, the physical properties of the sorbent mixtures must be similar. That is, a CeO{sub 2}-ZrO{sub 2} mixture from source A would not necessarily be superior to pure CeO{sub 2} from source B if the properties were dissimilar. Therefore, current research is concentrating on CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} mixtures prepared in this laboratory using the coprecipitation procedure. The structure of these sorbents is similar and the effect of ZrO{sub 2} addition can be separated from other effects. X-ray diffraction tests of the sorbents prepared in house have confirmed the existence of a solid solution of ZrO{sub 2} in CeO{sub 2}. Reduction tests using an electrobalance reactor have confirmed that CeO{sub 2}-ZrO{sub 2} mixtures are more easily reduced than pure CeO{sub 2}. Reduction of CeO{sub 2}-ZrO{sub 2} begins at a lower temperature and the final value of n in CeO{sub n} (1.5 <n < 2.0) is smaller in CeO{sub 2}-ZrO{sub 2} than in pure CeO{sub 2}. 700 C desulfurization tests have shown that both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents are capable of reaching the target sub-ppmv H{sub 2}S level in highly reducing gases. Some CeO{sub 2}-ZrO{sub 2} sorbents have successfully removed H{sub 2}S to the minimum detectable limit of the PFPD detector, approximately 100 ppbv

HIGH EFFICIENCY DESULFURIZATION OF SYNTHESIS GAS

Mixed metal oxides containing CeO{sub 2} and ZrO{sub 2} are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv or less H{sub 2}S. The research is justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeOn (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and should have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} were prepared. XRD analysis showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Unfortunately, the quantity of CeO{sub 2}-ZrO{sub 2} that could be prepared electrochemically was too small to permit full desulfurization testing. Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that may be exposed to low concentrations of H{sub 2}S are constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time is determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H{sub 2}S concentrations (<{approx}10 ppmv) and a thermal conductivity detector (TCD) for higher concentrations of H{sub 2}S. Larger quantities of CeO{sub 2}-ZrO{sub 2} mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, have been obtained. Much of the work during year 02 consisted of characterization and desulfurization testing of materials obtained from commercial sources. To properly evaluate the effect of ZrO{sub 2} addition on desulfurization capability, the physical properties of the sorbent must be similar. That is, a CeO{sub 2}-ZrO{sub 2} mixture from source A would not necessarily be superior to pure CeO{sub 2} from source B if the properties were dissimilar. Therefore, research during year 03 concentrated CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} mixtures prepared in this laboratory using the coprecipitation procedure. The structure of these sorbents is similar and the effect of ZrO{sub 2} addition can better be separated from other effects. X-ray diffraction tests of the sorbents prepared in house have confirmed the existence of a solid solution of ZrO{sub 2} in CeO{sub 2}. Reduction tests using an electrobalance reactor have confirmed that CeO{sub 2}-ZrO{sub 2} mixtures are more easily reduced than pure CeO{sub 2}. Reduction of CeO{sub 2}-ZrO{sub 2} begins at a lower temperature and the final value of n in CeO{sub n} (1.5 < n < 2.0) is smaller in CeO{sub 2}-ZrO{sub 2} than in pure CeO{sub 2}. Desulfurization tests have shown that both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents are capable of reaching the target sub-ppmv H{sub 2}S level in highly reducing gases. Both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents have successfully removed H{sub 2}S to the minimum detectable limit of the PFPD detector, approximately 100 ppbv

HIGH EFFICIENCY DESULFURIZATION OF SYNTHESIS GAS

Mixed metal oxides containing CeO{sub 2} and ZrO{sub 2} are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv of less H{sub 2}S. The research is justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeO{sub n} (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and should have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} has been developed and the products have been characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} have been prepared. XRD showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Phase separation did not occur when the solid solutions were heat treated at 700 C. A flow reactor system constructed of quartz and teflon has been constructed, and a gas chromatograph equipped with a pulsed flame photometric detector (PFPD) suitable for measuring sub-ppmv levels of H{sub 2}S has been purchased with LSU matching funds. Preliminary desulfurization tests using commercial CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} in highly reducing gas compositions has confirmed that CeO{sub 2}-ZrO{sub 2} is more effective than CeO{sub 2} in removing H{sub 2}S. At 700 C the product H{sub 2}S concentration using CeO{sub 2}-ZrO{sub 2} sorbent was near the 0.1 ppmv PFPD detection limit during the prebreakthrough period

HIGH EFFICIENCY DESULFURIZATION OF SYNTHESIS GAS

Mixed metal oxides containing ceria and zirconia have been studied as high temperature desulfurization sorbents with the objective of achieving the DOE Vision 21 target of 1 ppmv or less H{sub 2}S in the product gas. The research was justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeOn (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and was postulated to have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} mixtures was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} were prepared. XRD analysis showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Unfortunately, the quantity of CeO{sub 2}-ZrO{sub 2} that could be prepared electrochemically was too small to permit desulfurization testing. Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that were exposed to low concentrations of H{sub 2}S were constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time was determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H{sub 2}S concentrations from approximately 0.1 to 10 ppmv, and a thermal conductivity detector (TCD) for higher concentrations of H{sub 2}S. Larger quantities of CeO{sub 2}-ZrO{sub 2} mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, were obtained. Much of the work during year 02 consisted of characterization and desulfurization testing of materials obtained from commercial sources. Most of the commercial CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} materials were capable of reducing H{sub 2}S concentration from 5000 ppmv in highly reducing feed gas to less than 1 ppmv in the product gas. However, to properly evaluate the effect of ZrO{sub 2} addition on desulfurization capability, the physical properties of the sorbent must be similar. That is, a CeO{sub 2}-ZrO{sub 2} mixture from source A would not necessarily be superior to pure CeO{sub 2} from source B if the properties of the pure CeO{sub 2} were superior. Therefore, research during year 03 concentrated on CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} mixtures prepared in this laboratory using a coprecipitation procedure. The structural properties of these sorbents were similar and the effect of ZrO{sub 2} addition could better be separated from the structural effects. X-ray diffraction tests of the sorbents prepared in house confirmed the formation of a solid solution of ZrO{sub 2} in CeO{sub 2}. Crystallite sizes ranged from 12.7 to 18.8 nm and surface areas from 75 to 85 m{sup 2}/g. Reduction tests using an electrobalance reactor confirmed that CeO{sub 2}-ZrO{sub 2} mixtures were more easily reduced than pure CeO{sub 2}. Reduction of CeO{sub 2}-ZrO{sub 2} began at a lower temperature and the final value of n in CeO{sub n} (1.5 < n < 2.0) was smaller in CeO{sub 2}-ZrO{sub 2} than in pure CeO{sub 2}. Sorbent performance during desulfurization testing was judged both by the minimum H{sub 2}S concentration achieved during the so-called prebreakthrough period and by the duration of the prebreakthrough period. The end of the prebreakthrough period was defined as the time when the H{sub 2}S concentration in the product gas exceeded 1 ppmv. Both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents produced in house were capable of reaching the target sub-ppmv H{sub 2}S level in highly reducing gases for extended time periods. H{sub 2}S concentrations were reduced to levels approaching the minimum detectable limit of the PFPD detector, approximately 100 ppbv for time periods corresponding to as much as 60% sorbent sulfidation. The critical test of the sorbents was their performance when the reducing power of the feed gas was decreased by the addition of CO{sub 2} as an oxidant. While sub-ppmv levels of H{sub 2}S were still achieved using both CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} sorbents when the feed gas contained as much as 1% CO{sub 2}, the duration of the prebreakthrough time decreased as the CO{sub 2} concentration increased

Development of foam concrete with nitrogen oxides removal capability using various forms of titanium dioxide

Air quality in Seoul is significantly worse than in major OECD countries, with 1.2–3.5 times higher levels of fine dust and nitrogen dioxide. Photocatalytic reaction with Ca-bound catalyst efficiently removes nitrogen oxides (NOx), especially in building materials, promising solutions for NOx removal in urban air purification. This study therefore investigates the effect of various forms of titanium dioxide (TiO2) on the mechanical properties and NOx removal capability of foam concrete. To produce foam concrete, the type and amount of air foaming agent were optimized. Two types of commercially available TiO2 (P25 and NP600) were incorporated into the foam concrete, alongside synthesized TiO2-mayenite (as an intermixing powder or a coating material). Test results indicated that the incorporation of P25 and NP600 led to increased compressive strength and decreased porosity. The strength increased and porosity decreased, as the amount of TiO2 powders was increased. P25 outperformed NP600 in terms of the NOx removal capacity of foam concrete, with the peak NOx removal capacity (6.07 μmol/50 cm2·5 h) observed at a P25 content of 3%. An even higher NOx removal amount of 6.19 μmol/50 cm2·5 h was achieved by triple-coating the foam concrete surface with 10 wt% TiO2-mayenite. Considering the thickness of the coated TiO2-mayenite and economic feasibility, an approach with dual-coating emerged as the most suitable

Modification of Copper-Ceria Catalyst via Reverse Microemulsion Method and Study of the Effects of Surfactant on WGS Catalyst Activity

Some major drawbacks encountered in the synthesis of copper-ceria (Cu-CeO2)-based Water Gas Shift (WGS) catalyst via the conventional Impregnation (IMP) method are aggregate formation and nanoparticles’ instability. These lead to the poor interaction between Copper and Ceria, thereby impeding the catalytic activity with the inefficient utilization of active sites. To overcome these drawbacks, in this study, we described the synthesis of the Cu-CeO2 catalyst via the Reverse Microemulsion (RME) method with the help of the organic surfactant. This development of insights and strategies resulted in the preparation of porous particles with uniform size distribution and improved interaction within the composites, which were evident through XRD, XPS, BET Surface area, TPR, TEM and SEM analysis results. Remarkably, the optimum 20% Cu-CeO2 catalyst prepared by RME method was found to have superior Water Gas Shift (WGS) catalytic activity than the conventionally Impregnated catalyst when their CO conversion efficiencies were tested in WGS reaction at different feed gas compositions with and without CO2. Moreover, the 20% Cu-CeO2 sample prepared by RME method exhibited sustained catalytic activity throughout the entire 48 h period without any signs of deactivation. This observation highlights RME method as the potential pathway for developing more effective nanoparticle catalysts for hydrogen production, contributing to the growing demand for clean and sustainable energy sources

Enhanced Photovoltaic Performance of Novel TiO2 Photoelectrode on TCO Substrates for Dye-Sensitized Solar Cells

In this study, we report synthesis and growth of rutile-anatase TiO2 thin film on fluorine-doped tin oxide (FTO) glass by a two-step hydrothermal method. The effects of additional treatments (i.e., TiCl4 post-treatment and seed layer formation were also studied. Photocurrent-voltage (I-V) measurement of rutile-anatase TiO2 thin film was performed under 1.5 G light illumination. Photovoltaic performance was investigated by incident photon-to-electron conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent/ photovoltage spectroscopy (IMVS/IMPS) and open-circuit photovoltage decay (OCVD). Copyright © 2014 American Scientific Publishers. All rights reserved.

Hydrothermal synthesis of rutile-anatase TiO2 nanobranched arrays for efficient dye-sensitized solar cells

Rutile-anatase TiO2 nanobranched arrays were prepared in two sequential hydrothermal-synthesis steps. The morphologies and crystalline nanostructures of the samples were investigated by controlling growth time and the concentration of the titanium precursor. All samples were characterized by field-emission scanning electron microscopy and X-ray diffraction analysis. It was found that treating the surfaces of rutile TiO2 nanorods with aqueous TiCl4 solutions allows the anatase TiO2 nanobranches to grow perpendicular to the main rutile TiO2 nanorods attached to the FTO glass. Irregularly shaped, dense TiO2 structures formed in the absence of TiCl4 treatment. A light-to-electricity conversion efficiency of 3.45% was achieved using 2.3 μm tall TiO2 nanobranched arrays in a dye-sensitized solar cell. This value is significantly higher than that observed for pure rutile TiO2 nanorods. © 2014 Elsevier B.V. All rights reserved.