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The development of methodologies for CO2 utilization is in high demand worldwide. Here, we propose bifunctional tandem catalysts of ZnZrOx (for CO2-to-methanol hydrogenation) and a series of solid acid catalysts (for subsequent methanol conversion to light olefins). As solid acid catalysts, we used zeolites and silicoaluminophosphates with different topologies, MOR, FER, MFI, ∗BEA, CHA, and ERI, confirmed by X-ray diffraction, electron microscopy, and nitrogen adsorption-desorption. They also showed the corresponding acid properties examined by ammonia adsorption. The tandem catalysts realized a one-pass synthesis of lower olefins, while no hydrocarbons were obtained using ZnZrOx only. According to the reaction test and ammonia adsorption, there seems to be no correlation between product yields and acid strength. The pore sizes and channel dimensionality of zeolites influence the selectivity of products; zeolites with small pores, such as MOR, SAPO-34 and ERI, are promising, while zeolites with larger pores, such as MFI, produce heavier hydrocarbons. The results provide new insight into the design of innovative catalysts for CO2 utilization.

Electrolysis at intermediate temperatures (100-600 degrees C) is promising because high reaction rates and high product selectivity can be achieved simultaneously during CO2 reduction. However, intermediate temperature electrolysis has rarely been reported owing to electrolyte limntions. Here, solid acid electrolysis cells (SA:Cs) were adopted for electrochemically reducing CO2. Carbon monoxide, methane, methanol, ethane, ethylene, ethanol, acetaldehyde and propylene were produced from CO2 and steam, using Cu-containing composite cathodes at 220 degrees C and atmospheric pressure. The results demonstrate the potential of SAECs for producing valuable chemical feedstocks. At the SAEC cathode, CO2 was electrochemically reduced by protons and electrons. The product selectivity and reaction rate were considerably different from those of thermochemical reactions with gaseous hydrogen. Based on the differences, plausible reaction pathways were proposed.

Optimization of Pt-based electrode structure is a key to enhance power generation performance of fuel cells and to reduce the Pt loading. This paper presents a new methodology for anode fabrication for solid acid fuel cells (SAFCs) operating at ca. 200 °C. Our membrane electrode assembly for SAFCs consisted of a CsH2PO4/SiP2O7 composite electrolyte and Pt-based electrodes. To obtain the anode, a commercial Pt/C catalyst and carbon substance, such as carbon black and carbon nanofiber, were mixed. The composite anode with Pt loading = 0.5 mg cm−2 demonstrated superior current-voltage characteristics to a benchmark Pt/C anode with Pt loading = 1 mg cm−2. We consider that the mixing of Pt/C catalyst and carbon substrate facilitated H2 mass transfer and increased the number of active sites.

The effect of Ag loading (wt%) of Ag/CuO/ZrO2 catalysts for the CO2 hydrogenation to methanol was investigated. The addition of a small amount of Ag (≤1 wt%) to CuO/ZrO2 did not change the turnover frequency of methanol production per exposed Cu sites (TOFmethanol) but increased the selectivity towards methanol due to a synergy developed between Cu and Ag, which was supported by H2-TPR studies.

CO2 methanation over sponge Ni was investigated. When CO2 methanation was carried out using sponge Ni without any pretreatment, the sponge Ni exhibited a CO2 conversion of 83% at 250 °C under a high space velocity (0.11 molCO2 gcat−1 h−1). We think that the sponge Ni is a promising new catalyst for CO2 methanation because it showed the high activity even under the high GHSV, and we can design a small plug flow reactor compared to a conventional reactor, resulting in a low manufacturing cost for the reactor. The high activity can be derived from the great number of crystal defects of fcc-Ni in the sponge Ni. On the other hand, with high-temperature pretreatment, the sponge Ni lost its activity in CO2 methanation as well as the surface defect sites. Thus, the activity loss can be explained by the disappearance of the surface defect sites by the high-temperature pretreatment.

The effect of adding Ag to CuO-ZrO 2 catalysts for the hydrogenation of CO 2 to methanol was investigated using CuO-ZrO 2 , Ag/CuO-ZrO 2 , and Ag/ZrO 2 . The addition of Ag to CuO-ZrO 2 catalysts decreased the specific surface area and also broke its mesostructure. Thus, Ag played a significant role as a sintering aid in the preparation of Ag/CuO-ZrO 2 catalysts. We note that the as-prepared Ag/CuO-ZrO 2 catalysts contained Ag + and Zr q + ( q q + content increased with increasing Ag + content. Furthermore, the presence of CuO in the Ag/CuO-ZrO 2 catalyst appeared to stabilize Ag + and Zr q + species under air. Based on H 2 chemisorption and powder X-ray diffraction patterns, formation of a Ag-Cu alloy was observed on completely reduced and spent Ag/CuO-ZrO 2 catalysts. Completely reduced Ag/CuO-ZrO 2 catalysts exhibited a higher methanol production rate (7.5 mL h −1 g cat −1 ) compared to completely reduced CuO-ZrO 2 (6.9 mL h −1 g cat −1 ) and Ag/ZrO 2 catalysts (2.2 mL h −1 g cat −1 ) under the following reaction conditions: CO 2 /H 2 /N 2 = 1/3/1, catalyst loading = 500 mg, W/F total = 1000 mg cat s mL −1 , reaction temperature = 230 °C, pressure = 10 bar.

Perovskite-based catalysts with a self-regeneration property, named intelligent catalysts, were developed for CH4 partial oxidation, and the effect of redox treatment on regeneration behavior of the catalytic activity was investigated. Rh-substituted catalysts such as LaM0.95Rh0.05O3 (M: Cr, Co, Fe) were prepared by the Pechini method. Among the catalysts, LaCr0.95Rh0.05O3 exhibited the highest and the most stable catalytic activity for partial oxidation of methane before and after redox treatment. The precipitation and dissolution of Rh species were confirmed by X-ray photoelectron microscopy and transmission electron microscopy, indicating that the catalyst regenerated itself via the redox process.

This paper deals with CuO/ZrO2 catalysts with extremely high Cu loading and their catalytic activity for CO2 hydrogenation to methanol. Because of aiming an industrial application, we chose a flame spray pyrolysis (FSP) technique as a simple and rapid catalyst preparation method. Thanks to the FSP, we succeeded to prepare 20–80 wt% CuO/ZrO2 catalysts. Interestingly, the catalyst structure changed with the Cu loading. In the case of Cu loading = 20 wt%, CuO nanoparticles (ca. 5 nm) were supported on tetragonal ZrO2 particles (5–10 nm), observed by high-angle annular dark-field scanning transmission electron microscopy. Of note, the catalyst with 60 wt% of Cu was ZrO2@CuO core-shell nanoparticles: ZrO2 aggregates were covered with many CuO nanoparticles (

Selective CO methanation was carried out over 10 wt%Ni/TiO 2 and 0.5 wt%Ru–10 wt%Ni/TiO 2 , and the durability was examined. During the long-term test, both catalysts abated CO concentration from 0.25% (dry base) to less than 0.05% above ca. 175 °C with CO 2 methanation suppressed. Ru–Ni/TiO 2 exhibited the high activity of CO methanation compared to Ni/TiO 2 during the test. Furthermore, for more than 5500 h, Ru–Ni/TiO 2 maintained a wide temperature window for selective CO methanation (>50 °C), where CO and CH 4 concentrations were −1 . Over Ni/TiO 2 and Ru–Ni/TiO 2 , CO 2 methanation activity was initially enhanced, and then stabilized. The initial promotion of CO 2 methanation activity is possibly due to the reduction of NiO which remained unreduced after the prereduction by H 2 at 450 °C.

Selective CO methanation over Ru/TiO2, Ru-Ni/TiO2, Ru-Co/TiO2, Ru-Fe/TiO2, Ru-La/TiO2, Ru-K/TiO2, and Ru-Ni-La/TiO2 was investigated as a CO removal method from reformate gas for polymer electrolyte fuel cell applications, and the selectivity and activity were examined. The addition of Co and La to Ru/TiO2 improved both CO and CO2 methanation, while the addition of Ni raised only the activity for CO methanation. The addition of La increased the electron density in the Ru species, which likely enhanced the dissociation of the C O bond of CO on Ru probably due to back donation of electrons from Ru to CO. This led to high CO methanation activity over Ru-La/TiO2. The trimetallic catalyst Ru-Ni-La/TiO2 showed the highest CO methanation activity among the prepared catalysts, resulting in a wider temperature range for selective CO methanation at low temperatures compared to Ru/TiO2.

The removal of CO from hydrogen-rich gas produced by steam reforming of hydrocarbons by selective CO methanation was investigated over xwt%Ru–ywt%Ni/TiO2 (x = 0, 0.2, 0.3, 0.4, y = 0, 5, 9). The bimetallic catalyst Ru–Ni/TiO2 exhibited higher activity of CO methanation at low temperatures and lower activity of CO2 methanation at high temperatures than Ru/TiO2. Especially, 0.2 wt%Ru–9 wt%Ni/TiO2 was the most suitable catalyst for selective CO methanation. As for the prepared Ru–Ni/TiO2 catalysts, the reverse water gas shift (RWGS) reaction was accelerated with an increase in the Ru loadings. Consequently the 0.2 wt%Ru–9 wt%Ni/TiO2 produced little CO due to the low activity of RWGS reaction, resulting in rapid abatement of CO at low temperatures and low production of CH4 at high temperatures compared to 0.3 wt%Ru–9 wt%Ni/TiO2 and 0.4 wt%Ru–9 wt%Ni/TiO2.

The effect of CeO 2 loading amount of Ru/CeO 2 /Al 2 O 3 on CO 2 methanation activity and CH 4 selectivity was studied. The CO 2 reaction rate was increased by adding CeO 2 to Ru/Al 2 O 3 , and the order of CO 2 reaction rate at 250 °C is Ru/30%CeO 2 /Al 2 O 3 > Ru/60%CeO 2 /Al 2 O 3 > Ru/CeO 2 > Ru/Al 2 O 3 . With a decrease in CeO 2 loading of Ru/CeO 2 /Al 2 O 3 from 98% to 30%, partial reduction of CeO 2 surface was promoted and the specific surface area was enlarged. Furthermore, it was observed using FTIR technique that intermediates of CO 2 methanation, such as formate and carbonate species, reacted with H 2 faster over Ru/30%CeO 2 /Al 2 O 3 and Ru/CeO 2 than over Ru/Al 2 O 3 . These could result in the high CO 2 reaction rate over CeO 2 -containing catalysts. As for the selectivity to CH 4 , Ru/30%CeO 2 /Al 2 O 3 exhibited high CH 4 selectivity compared with Ru/CeO 2 , due to prompt CO conversion into CH 4 over Ru/30%CeO 2 /Al 2 O 3 .

The removal of CO from reformate streams by selective CO methanation was investigated over TiO 2 supported Ru Ni bimetallic and monometallic catalysts. The combination of Ru and Ni enhanced CO methanation at low temperatures. The introduction of Ni into Ru/TiO 2 decreased the CO 2 conversion rate at 260 °C from 10 to 7.3 μmol min −1 g cat −1 . The use of Ru and Ni, thus, expands the temperature range of selective CO methanation. Transmission electron microscopy and temperature programmed reduction by H 2 confirmed that Ru species were in close proximity to Ni species on Ru Ni/TiO 2 , indicating a decrease in direct contact between Ru and TiO 2 . Fourier transform infrared spectroscopy techniques revealed that the decomposition of the formate species, formed during CO 2 methanation, is slow over Ru Ni/TiO 2 , in contrast to Ru/TiO 2 .

Selective CO methanation over Ru/Al 2 O 3 and Ru/TiO 2 was investigated as a CO removal method from reforming gas, and the effect of reduction treatment and the support materials on the selectivity and activity was examined. CO methanation activity was degraded over both Ru catalysts by raising reduction treatment temperature, which brought about Ru particle growth except for Ru/TiO 2 reduced at 600 °C. Ru/TiO 2 showed higher CO methanation activity than Ru/Al 2 O 3 due to smaller Ru particle size. A close correlation was found between CO 2 methanation rate and interfacial length of Ru particle and support, which indicates that the interface was identified as the reaction sites of CO 2 methanation in CO and CO 2 coexisting atmosphere. CO 2 methanation over Ru/TiO 2 was suppressed in spite of long length of the interface compared to Ru/Al 2 O 3 , stemming from the small amount of CO 2 adsorbed onto Ru/TiO 2 . Ru/TiO 2 catalyst exhibited wider temperature window for selective CO methanation than Ru/Al 2 O 3 catalyst.