Preferential oxidation of carbon monoxide in simulated reformatted gas over PtAu/CexZnyO2 catalysts

A series of Pt–Au catalysts prepared by co-precipitation (CP) and single step sol-gel (SSG) methods was investigated for selective CO oxidation. The characteristics of the prepared catalysts were determined by XRD, BET surface area, SEM, H₂-TPR, chemisorption analysis, and FTIR. The simulated reformatted gas consisted of 1% CO, 1% O₂, 0% to 10% H₂O, 0–20% CO₂, and 40% H₂ in He balance. The operating temperature range was varied from 50 °C to 190 °C at atmospheric pressure. The experimental results elucidated that the catalytic preparation method had a significant effect on the catalyst characteristics and its activity. The catalytic performance over PtAu/Ce₁Zn₁O₂ prepared by co-precipitation was higher than that of PtAu/CeO₂ and PtAu/ZnO because of the incorporation of Ce⁴⁺ ions and the Zn²⁺ ions in the lattice. To encourage better catalytic performance, the catalysts should be calcined at 500 °C for 5 h and pretreated in a H₂ atmosphere. The CO conversion for the single- and double-stage reaction was reduced when adding water vapor and CO₂ to the feedstream; the water vapor and CO₂ molecules compete for the adsorption with CO on the active sites of the catalysts. During the deactivation test for 60 h, the CO conversion and selectivity are maintained.     

Single- and double-stage catalytic preferential CO oxidation in H2-rich stream over an α-Fe2O3-promoted CuO–CeO2 catalyst

Single- and double-stage catalytic preferential CO oxidation (CO-PrOx) over-Fe₂O₃-promoted CuO–CeO₂ in a H₂-rich stream has been investigated in this work. The catalyst was prepared by the urea-nitrate combustion method and was characterized by X-ray diffractometer (XRD), X-ray fluorescence (XRF), Brunauer–Emmet–Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM). The catalytic activity tests were carried out in the temperature range of 50–225 °C under atmospheric pressure. The results of the single-stage reaction indicated that complete CO oxidation was obtained when operating at a O₂/CO ratio of 1.5, W/F ratio of 0.36 g s/cm³, and at a reaction temperature of 175 °C. At these conditions, H₂ consumption in the oxidation was estimated at 58.4%. Applying the same conditions to the double-stage reaction, complete CO oxidation was found and H₂ consumption in the oxidation was reduced about 4.9%. When decreasing the double-stage reaction temperature to 150 °C, the results elucidated that CO could be converted to CO₂ completely while H₂ consumption in the oxidation was further reduced to 33.5%. A temperature blocking 2² factorial design has been used to describe the importance of the factors influencing the catalytic activity. The factorial design was according to the experimental results. When adding CO₂ and H₂O in feed, reduction of CO conversion for single- and double-stage reaction is obtained due to a blocking of CO₂ and H₂O at a catalytic active site. Comparing CO conversion obtained when operating with/without CO₂ and H₂O in feed for single- and double-stage reaction, less reduction is achieved when operating in double-stage reaction.     

Preferential oxidation of carbon monoxide over Pt, Au monometallic catalyst, and Pt–Au bimetallic catalyst supported on ceria in hydrogen-rich reformate

The objective of this paper was to study a preferential oxidation (PROX) of carbon monoxide over monometallic catalysts including Pt, Au and Pt–Au bimetallic catalyst supported on ceria in hydrogen-rich reformate. Single step sol–gel method (SSG) and impregnation on sol–gel method (ISG) were chosen for the preparation of the catalysts. The characteristics of these catalysts were investigated by X-ray diffractometer (XRD), Brunauer–Emmet–Teller (BET) method, transmission electron microscope (TEM), scanning electron microscope (SEM) and temperature-programmed reduction (TPR). The XRD patterns of the catalysts showed only the peaks of ceria crystallite and no metal peak appeared. From TEM images, the active components were seen to be dispersed throughout the ceria support. The TPR patterns of PtAu/CeO₂ catalyst prepared by SSG showed the reduction peaks were within a low temperature range and therefore, the catalysts prepared by SSG exhibited excellent catalytic activity for preferential oxidation of CO. Bimetallic Pt–Au catalyst improved the activity (90% conversion and 50% selectivity at 90 °C) because of the formation of a new phase. When the metal content of (1:1) PtAu/CeO₂ catalyst prepared by SSG was increased, the CO conversion did not change much while the selectivity decreased in the low temperature range (50–90 °C). The CO conversion increased with increasing W/F ratio. The presence of CO₂ and H₂O had a negative effect on CO conversion and selectivity due to blocking of carbonate and water on active sites.     

Effect of synthesis time on morphology of CeO_2 nanoparticles and Au/CeO_2 and their activity in oxidative steam reforming of methanol

Ceria(CeO_2)supports,synthesized by hydrothermal treatment with different synthesis time(CeO_2-X h,where X is the synthesis time in h)in the presence of the surfactant cetyltrimethyl ammonium bromide,were used as supports for gold(Au)catalysts.The synthesis time significantly affects the morphological structure and crystallite size of CeO_2,where CeO_2-2 h has the smallest crystallite size with coexisting nanorods and nanoparticles.Transmission electron microscopy analysis confirms the morphology of CeO_2 with distinctive(110),(100)and(111)planes,in agreement with interplanar spacings of 0.19,0,27 and 0.31,respectively.However,the morphology of CeO_2-8 h and CeO_2-48 h is mainly a truncated octahedral with crystal planes(111)and(100)accompanied by an interplanar spacing of 0.31 and0.27 nm,respectively.The CeO_2-X h supports and those with a 3 wt%Au loading(Au/CeO_2-X h)were investigated in the oxidative steam reforming of methanol at temperatures between 200 and 400 ℃.The Au/CeO_2-2 h gave the highest methanol conversion level and hydrogen yield at a low temperature of 250 ℃.This superior catalytic performance results from the good interaction between the metal and support and the well-distributed Au species on the CeO_2 support.     

Applying a face-centered central composite design to optimize the preferential CO oxidation over a PtAu/CeO2–ZnO catalyst

The catalytic performance for the preferential oxidation of CO over a 1% (w/w) PtAu/CeO₂–ZnO catalyst prepared by co-precipitation was investigated using a full 2^k factorial design with three central points and a 95% confidence interval, in order to screen for the importance of the operating temperature (°C) and the H₂O and CO₂ contents (%) in the simulated reformate gas on the CO conversion and selectivity. The catalyst was characterized by TEM, BET, XRD and FTIR. The temperature and CO₂ content had a significant influence on the conversion, whilst the selectivity depended on the temperature only. A face-centered central composite design was then used to evaluate the optimal conditions by simultaneously considering the maximal conversion, selectivity and constraints of the composition of realistic reformate gas. The difference in the estimated response and the experimental one was within ±2% and ±3% for routing simulated and realistic reformate gases, respectively.     

Water-gas shift reaction over Cu–Zn,Cu–Fe,and Cu–Zn–Fe composite-oxide catalysts prepared by urea-nitrate combustion

Water-gas shift reaction was investigated over Cu–Zn, Cu–Fe and Cu–Zn–Fe composite-oxide catalysts at atmospheric pressure from 200 to 375 °C in terms of reducing the CO content with maximal H₂ yield. The Cu_0.15ZnFe₂ spinel catalyst expressed a higher CO conversion level and H₂ yield at a lower temperature compared to the Cu_0.15Zn and Cu_0.15Fe catalysts. Adding H₂O to the feed up to 30% (v/v), but not above, increased the CO reduction level, presumably by increasing the hydroxyl species to react with the adsorbed CO. Increasing the W/F ratio to 0.24 g s cm^?3 increased the CO conversion level to 0.76 at 275 °C with the Cu_0.15ZnFe₂ catalyst, and could be further increased to 0.86 at 350 °C by increasing the Cu molar ratio to 0.30 (Cu_0.30ZnFe₂). Nevertheless, increasing the Cu molar content to 0.50 reduced the CO conversion level. No requirement for adding O₂ when using the Cu_0.30ZnFe₂ catalyst at >260 °C was observed. Increasing the CO content in the reactant decreased its conversion level. The performance of the Cu_0.30ZnFe₂ catalyst was stable over a test period in a CO-rich condition. No undesired product was detected, suggesting a higher selectivity for hydrogen production with a low CO content.     

Hydrogen production via methanol steam reforming over Au/CuO,Au/CeO2, and Au/CuO–CeO2 catalysts prepared by deposition–precipitation

The production of hydrogen (H₂) with a low concentration of carbon monoxide (CO) via steam reforming of methanol (SRM) over Au/CuO, Au/CeO₂, (50:50)CuO–CeO₂, Au/(50:50)CuO–CeO₂, and commercial MegaMax 700 catalysts were investigated over reaction temperatures between 200 °C and 300 °C at atmospheric pressure. Au loading in the catalysts was maintained at 5 wt%. Supports were prepared by co-precipitation (CP) whilst all prepared catalysts were synthesized by deposition–precipitation (DP). The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM). Au/(50:50)CuO–CeO₂ catalysts expressed a higher methanol conversion with negligible amount of CO than the others due to the integration of CuO particles into the CeO₂ lattice, as evidenced by XRD, and a interaction of Au and CuO species, as evidenced by TPR. A 50:50 Cu:Ce atomic ratio was optimal for Au supported on CuO–CeO₂ catalysts which can then promote SRM. Increasing the reaction time, by reducing the liquid feed rate from 3 to 1.5 cm³ h^?1, resulted in a catalytic activity with complete (100%) methanol conversion, and a H₂ and CO selectivity of ～82% and ～1.3%, respectively. From stability testing, Au/(50:50)CuO–CeO₂ catalysts were still active for 540 min use even though the CuO was reduced to metallic Cu, as evidenced by XRD. Therefore, it can be concluded that metallic Cu is one of active components of the catalysts for SRM.     

Hydrogen production with a low carbon monoxide content via methanol steam reforming over CuxCeyMgz/Al2O3 catalysts: Optimization and stability

Catalytic activities of Ce–Mg promoted Cu/Al₂O₃ catalysts via methanol steam reforming was investigated in terms of the methanol conversion level, carbon monoxide selectivity and hydrogen yield. The factors chosen were the reaction temperature, copper content, Mg/(Ce + Mg) weight-percentage and steam to carbon ratios. The catalysts were prepared by co-precipitation and characterized by means of XRD, BET, H₂-TPR, and FESEM. The Ce–Mg bi-promoter catalysts gave higher performance due to magnesium penetration into the cerium structure causing oxygen vacancy defects on the ceria. A response-surface-model was then designed to optimize the condition at a 95% confidence interval for complete methanol conversion to a high H₂ yield with a low CO content, and revealed an optimal copper level of 46–50 wt%, Mg/(Ce + Mg) of 16.2–18.0%, temperature of 245–250 °C and S/C ratio of 1.74–1.80. No deactivation of the Cu_0.5Ce_0.25Mg_0.05/Al catalyst was observed during a 72-h stability test.