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Cobalt-, iron-, and copper-substituted nickel-aluminum hydrotalcite-like compounds (Ni2.7Co0.3Al, Ni2.7Fe0.3Al, Ni2.7Cu0.3Al HTlcs) have been synthesized and used as precursors to prepare Ni–Co, Ni–Fe, and Ni–Cu alloy catalysts for methane decomposition. The catalysts before and after reaction were characterized with various techniques including XRD, H2-TPR, HAADF-STEM-EDX, SEM, TEM, and Raman. The characterization results indicate that upon calcination HTlcs are transformed into a mixed oxide solid solution, where cobalt, copper, and iron ions are incorporated into the nickel oxide, and the reduction treatment leads to composition-uniform alloy particles. In methane decomposition at 600 °C, alloying Ni with Co, Fe, and especially Cu is found to enhance the catalytic life and carbon yield. The order of activity is Ni2.7Cu0.3Al >> Ni2.7Fe0.3Al > Ni2.7Co0.3Al > Ni3Al in terms of carbon yield, highlighting that Ni–Cu alloying is the most effective. Besides, Ni–Cu alloying remarkably changes the carbon morphology, giving carbon nanofibers as the main product. TEM and STEM measurements suggest that Ni–Cu alloy particles are readily aggregated into big particles (>60 nm) under the reaction conditions, which may be responsible for the significant effect of Ni–Cu alloying.

Various Ni–Fe/Mg(Al)O alloy catalysts were obtained by calcination of Ni–Fe–Mg–Al hydrotalcite-like compounds, followed by reduction at different temperatures (973–1173 K). The characterizations of XRD and STEM-EDX suggest that the resulting Ni–Fe alloy particles are composition-uniform and size-controllable. The alloy composition is little affected by the reduction temperature, whereas the particle size (5.8–8.2 nm) increases with the increase of reduction temperature. This property is ascribed to the homogeneous distribution of nickel and iron species during the catalyst preparation. All of the Ni–Fe/Mg(Al)O alloy catalysts show relatively high and stable activity for CH4–CO2 reforming during 25 h of investigation at 773–1073 K. Particularly, the 973 K-reduced catalyst exhibits higher coke-resistance due to its smaller particle size. Ea-CH4 and CH4-TPSR measurements indicate that Ni–Fe alloying inhibits CH4 dissociation. It is considered that during DRM CH4 is dissociated at the Ni sites and CO2 may be activated at the metal-support interface as well as the Fe sites. Ni–Fe alloying may inhibit CH4 dissociation and/or promote CO2 activation, thus contributing to the suppression of coke deposition.

A series of Ni catalysts were prepared from Ni–Al hydrotalcite-like compounds (HTlcs) by varying the Ni/Al molar ratio (1–4) and calcination temperature (773–1173 K) of HTlcs. The catalysts were reduced with H2 at 1073 K and tested for CH4 decomposition at 773–923 K on a thermal gravimeter. Various techniques including N2 physical adsorption, XRD, H2-TPR, XPS, HAADF-STEM, TEM, and Raman were applied to characterize the catalysts and the as-produced carbon. The characterizations show that calcination of Ni–Al HTlcs leads to Ni(Al)O solid solution and minor NiO and/or NiAl2O4 spinel may be formed depending on the Ni/Al ratio and calcination temperature; upon reduction at 1073 K, most nickel species are reduced to metallic Ni. In CH4 decomposition, carbon yield shows a volcano-type dependence on the Ni content with the optimum Ni/Al ratio equal to 3. On the other hand, carbon yield is affected by the calcination temperature of the Ni3Al HTlcs to a small extent. Carbon yield is also significantly affected by the reaction temperature, which decreases remarkably with a rise of temperature to 923 K. TEM and Raman indicate that fish-bone carbon nanofibers are formed at 773–823 K, whereas multi-walled carbon nanotubes are formed at 873–923 K.

Hydrotalcite-derived Ni/Mg(Al)O is promising for CH4–CO2 reforming. However, the catalysts reported so far suffer from sever coking at low temperatures. In this work, we demonstrate that a significant improvement of coke-resistance of Ni/Mg(Al)O can be achieved by fine tuning the Ni particle size through adjusting the reduction condition of catalyst. Ni particles having average size within 4.0–7.1 nm are in situ generated by reducing the catalyst at a selected temperature within 923–1073 K. Controllability of Ni particle size is related to the formation of Mg(Ni,Al)O solid solution upon hydrotalcite decomposition. It is found that the catalyst reduced at 973 K exhibits high activity, stability, and coke-resistance even at reaction temperature as low as 773 K. In contrast, the catalyst reduced at 923 K has low activity and deactivates due to Ni oxidation, while those reduced at 1023 and 1073 K suffer from sintering and severe coking. STEM and O2-TPO reveal that coke deposition is directly proportional to the Ni particle size but becomes negligible at a size below 6.2 nm. It is evidenced that a critical size of about 6 nm is required to inhibit coking effectively. CO2 temperature-programmed surface reaction indicates that the deposited carbon on small Ni particles can be easily removed by the CO2 activated at the Ni–Mg(Al)O interfaces, accounting for the better resistance to coking.

CuO/CeO2 is a kind of promising catalysts for the water-gas shift (WGS) reaction. Efforts were put in to improve its performance through modification of CeO2 support. In this study, portions of CeO2 prepared by a co-precipitation method were separately annealed at 300 °C in air, under vacuum and with H2 , and were used as supports for the fabrication of CuO/CeO2 catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction, N2 -physisorption, inductively coupled plasma, Raman spectroscopy, CO2 temperature-programmed desorption, and H2 temperature-programmed reduction techniques. The relation between catalytic performances and physicochemical properties of the CuO/CeO2 catalysts were discussed. Among the three catalysts, the one with CuO supported on H2 -reduced CeO2 shows the highest catalytic activity, mainly due to strong CuO-CeO2 synergetic interaction and high concentration of Frenkel-type oxygen vacancies. The superior catalytic activities can also be attributed to the Cu0 crystals of small size and the oxygen vacancies in non-stoichiometric CeO2-x .

A series of Mg-Al-Ce mixed oxides with (nMg2+)/(nCe3+ + nAl3+) = 5 and nCe3+/(nCe3+ + nAl3+) = 0 ∼ 7% were synthesized by co-precipitation method based on a hydrotalcite route and used as support to prepare Co-Mo sulfur-resistant water-gas shift (WGS) catalysts. The supports and catalysts were characterized by XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS, TEM, and CO-IR. It is found that the catalytic performance and physicochemical property of the Co-Mo/Mg(Al)O catalyst are significantly influenced by the Ce modification. The addition of Ce effectively enhances the WGS activity and the highest activity is obtained on the Co-Mo/Mg(Al)O-CeO2 (5%) catalyst, where the activity at 623 K increases about 2.5 times. The results of H2S-TPS investigation show that in the presence of Ce, the H2S consumption peak shifts to lower temperatures and there is decrease of Mo sulfidation activation energy. Furthermore, HRTEM analysis shows that the addition of Ce (5%) results in decrease of MoS2 slab length and stacking number, and those of CO-IR characterization indicate increased exposure of surface MoS2 sites. It is suggested that the addition of Ce promotes the formation of MoS2 slabs that are smaller in size, leading to higher exposure of surface active sites and hence higher activity.

The Co catalyst using hydrotalcite-derived Mg(Al)O as support shows promising catalytic activity for low-temperature CH4-CO2 reforming. Under a wide range of reaction conditions, that is T = 773–1023 K, CH4/CO2/N2 = 25/25/50–50/25/25, WHSV = 60,000–120,000 mL h−1 g−1, and TOS = 25–200 h, the Co catalyst exhibits stable activity and high coke resistance. The performance is superior to the Ni counterpart which readily deactivates at 773 K due to severe coke deposition. The initial coking rate on the Co catalyst was estimated to be about 1/20 times that on the Ni catalyst. The kinetic study suggests that the dissociative adsorption of CH4 is favored on the Ni catalyst, whereas the Co catalyst has high affinity for CO2 adsorption. The results of CH4-TPSR and direct CH4 decomposition experiments further reveal that the Co catalyst is much less active for carbon formation through CH4 decomposition. It is deduced that a combination of lower activity for CH4 dissociation/decomposition and higher affinity for CO2 adsorption as well as a stronger metal-support interaction is responsible for the higher coke resistance of the Co catalyst.

Six kinds of functionalized multiwalled carbon nanotubes (FCNTs) with different functional moieties were utilized as metal-free electrocatalysts towards the hydrogen evolution reaction for the first time. Ethylenediamine-functionalized multiwalled carbon nanotubes (EDA-CNTs) delivered the best HER activity holding a low-onset overpotential of 150 mV, a Tafel slope of 116 mV dec−1, and a Faradaic efficiency (FE) of 94% with a good stability. This HER activity of EDA-CNTs is superior or quite comparable to other reported metal-free HER catalysts, while the preparation of this electrocatalyst is simple, quick, and inexpensive. This good HER performance of EDA-CNTs can be resulted from the high electrical conductivity and its high grafting yield to form more amide groups for enhancement of proton adsorption. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were successfully used to elucidate the HER process promoted by EDA-CNTs, in which the amide groups were demonstrated to improve the proton adsorption.

Hydrotalcite-like compounds (HTlcs) are promising supports or catalyst precursors for heterogeneous catalysts. Herein, MgAl-HTlcs-supported Pd catalyst was fabricated, and two Pd catalysts supported on Mg(OH)2 and Al(OH)3 were prepared for comparison. The presence of hydroxyl groups (OH-) in the support is important for obtaining uniform Pd nanoparticles with small sizes. We found that Pdn+ species are more active than Pd0 in low temperature CO oxidation due to their lower barrier in CO activation. The Pd/MgAl-HT catalyst shows the most stable Pdn+ at a temperature lower than 90 °C, leading to the highest catalytic activity towards CO oxidation. Pdn+ in the Pd/Al(OH)3 catalyst is more stable than that in Pd/Mg(OH)2 at low temperature, which is ascribed to its smaller temperature hysteresis (Thysteresis) between the oxidation and re-reduction cycles. The effect of hydroxyl groups on stabilizing Pd species is related to the stability of Pd catalyst in CO oxidation reaction.

Cu/ZnO/Al2O3 catalysts with different compositions were prepared from Cu–Zn–Al layered double hydroxides (LDHs) and tested for the water–gas shift reaction. LDHs were synthesized by the coprecipitation method, and Cu–Zn–Al LDHs or Cu–Al LDHs could be formed depending on the (Cu + Zn)/Al atomic ratio. Upon calcination, LDHs decomposed to form mixed metal oxides consisting of CuO, ZnO, ZnAl2O4, CuAl2O4, and/or amorphous Al2O3. After reduction, well dispersed Cu metal particles with 18–48% dispersion and 2–6 nm size were formed. It was observed that the initial activity of Cu/ZnO/Al2O3 catalysts was proportional to the number of surface Cu0 atoms and the 30%Cu/Zn1Al catalyst showed the highest activity. Moreover, this optimum catalyst exhibited better activity, thermal stability, and long-term stability than a commercial Cu/ZnO/Al2O3 catalyst. It was considered that a synergetic effect between Cu metal and ZnAl2O4 spinel might exist and play a key role for the high catalytic performance.

Mg(Al)O mixed oxide-supported Co catalysts were prepared by using Co–Mg–Al layered double hydroxides (LDHs) as precursors and their structural and catalytic properties for CH4–CO2 reforming were studied. Upon calcination and reduction, Co–Mg–Al LDHs were decomposed to Mg(Co, Al)O mixed oxides and gave rise to highly dispersed Co metal particles with the mean size of ∼9–10 nm. The catalytic activity, stability, and coke resistance of Co/MgAl increased with the increase of Co loading. The 12%–15%Co/Mg3Al catalysts showed high and stable activity as well as less coke deposition during 30 h of reaction at 1023 K. Sintering of Co particles was not clearly observed, indicative of good thermal stability of Co particles, and this could be attributed to the strong metal-support interaction between Co particles and Mg(Al)O. It was also found that the optimum LDHs-Co/MgAl catalyst exhibited superior coke resistance than the LDHs-Ni/MgAl catalyst. Particularly during 25 h of reaction at 873 K, the 12%Co/Mg3Al catalyst showed much higher catalytic stability and much less coke deposition as compared to the 12%Ni/Mg3Al catalyst, highlighting the great potential of using Co instead of Ni as an active catalyst for the CH4–CO2 reforming.

Ru catalysts (2 wt%) supported on Mg and/or Al oxides including γ-Al 2 O 3 , MgAl 2 O 4 , Mg 3 (Al)O, and MgO were prepared by incipient wetness impregnation and compared for the CH 4 -CO 2 reforming to investigate the effect of support on the Ru dispersion and catalytic performance. The catalysts before and after reaction were well characterized by using N 2 physical adsorption, ICP, SEM-EDX, XRD, H 2 -TPR, TEM, CO chemisorption, FTIR of CO adsorption, XPS, CO 2 -TPD, TG, and Raman spectroscopy. The characterization results revealed that Ru metal was very highly dispersed on the Mg 3 (Al)O mixed oxide obtained from Mg-Al layered double hydroxide, probably existing in very small nanoparticles and/or clusters. The order of Ru metal dispersion was Ru/Mg 3 (Al)O > Ru/MgO > Ru/MgAl 2 O 4 > Ru/γ-Al 2 O 3 . The catalytic activity and stability of the Ru catalysts were greatly dependent on the support. Both Ru/MgO and Ru/Mg 3 (Al)O showed higher activity than Ru/MgAl 2 O 4 and Ru/γ-Al 2 O 3 , which might be related to the strong base intensity of support and more accessible surface Ru 0 atoms, respectively. During 30 h of reaction at 1023 K, a significant deactivation occurred on Ru/γ-Al 2 O 3 , Ru/MgAl 2 O 4 , and Ru/MgO, which was mainly attributed to the sintering of Ru metal particles. In contrast, the Ru/Mg 3 (Al)O catalyst exhibited superior stability and no significant sintering of Ru metal was observed, suggesting that the highly dispersed Ru metal was stable. A 300 h long-term test further demonstrated the excellent stability of Ru/Mg 3 (Al)O. These results highlight the significant effect of Mg(Al)O mixed oxide on the improvement of Ru dispersion and catalytic performance, and this might be related to the unique properties of Mg(Al)O mixed oxide including memory effect, low crystallinity, and its strong interaction with Ru.

Mixed metal oxides Co 5 − x Cu x Al ( x = 0–0.5) were prepared from Co-Cu-Al layered double hydroxides (LDHs) and tested for benzene total oxidation. By calcination, Co-Cu-Al LDHs were mainly transformed to (Co, Cu)(Co, Al) 2 O 4 spinels, where both Cu 2 + and Al 3 + cations were incorporated into the spinel structure. The incorporation of Cu significantly improved the Co oxide reducibility and remarkably enhanced the light-off activity as well as the total conversion activity, indicative a strong interaction between Cu 2 + and Co 3 + active sites. The optimum Co 4.75 Cu 0.25 Al spinel mixed oxide was comparable with a 0.3%Pd/γ-Al 2 O 3 catalyst, highlighting the promoting effect of structural modification with Cu.

Mg(Al)O mixed metal oxide (MMO) supported Cu nanoparticles catalysts have been prepared by calcination and reduction of Cu-Mg-Al layered double hydroxides (LDHs). By adjusting the chemical compositions of LDHs precursors, various catalysts with 10–40 wt% Cu content and molar ratio of (Cu + Mg)/Al = 1–4 were prepared. The catalysts were characterized by ICP, N 2 physical adsorption, XRD, TEM, H 2 -TPR, and N 2 O chemisorption, and tested for the water-gas shift (WGS) reaction. The characterization results suggested that upon calcination Cu-Mg-Al LDHs were converted to Mg(Cu, Al)O MMOs, where both Cu 2+ and Al 3+ were incorporated into the MgO framework to form a solid solution; reduction of Mg(Cu, Al)O gave highly dispersed and uniform Cu metal nanoparticles. The Cu metal dispersion was as high as 22–78% and the particle size varied from 1.5 to 5 nm depending on the chemical compositions. The WGS activity of the Cu catalysts increased with the increase of Cu 0 surface area. Among the prepared catalysts, the 30%Cu/Mg 2 Al catalyst exhibited the highest Cu surface area and the highest WGS activity. The optimized catalyst also showed superior activity, thermal stability, and steady-state stability than a commercial Cu/ZnO/Al 2 O 3 catalyst under the present reaction conditions. The characterization on the spent catalysts showed that the LDHs-derived Cu nanoparticles remained highly dispersed, suggesting that the Mg(Al)O supported Cu nanoparticles were stable and possessed good resistance against sintering.

A biodegradable adsorbent, modified konjac glucomannan (MKGM), was prepared by konjac glucomannan (KGM) acylated with phthalic anhydride catalyzed using concentrated sulfuric acid. The modified conditions such as reaction temperature, mass ratio of phthalic anhydride to KGM, catalyst dosage and reaction time were investigated, respectively. MKGM exhibited preferable adsorption performance for the removal of Fe (Ⅲ) ion. The adsorption behavior was discussed using the Langmuir and Freundlich isotherm models. The results showed that the Freundlich linear model was suitable for describing the adsorption process of Fe (Ⅲ). The maximum adsorption capacity of MKGM for Fe (Ⅲ) ion was 31.87 mg g−1 at 298 K. The kinetics studies suggested that adsorption process followed the pseudo-second-order model and the adsorption process was mainly controlled by both surface reactivity and intra-particle diffusion. Together with the evaluation of the thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes, the results indicated that the adsorption process of Fe (Ⅲ) was endothermic, feasible, and spontaneous in nature. Hence, as a bioadsorbent, the MKGM has a promising potential for the removal of Fe (Ⅲ) ion from aqueous solutions.

Supported Ni-Cu alloy nanoparticles prepared from Ni-Cu-Mg-Al hydrotalcite-like compounds (HTlcs) with Cu/Ni = 0.25 have been shown to be an active catalyst for the steam reforming of tar derived from the biomass pyrolysis. In the present work, Ni-Cu alloy catalysts with wider compositions of Cu/Ni were characterized and their performances were evaluated in the steam reforming of 1-methylnaphthalene (1-MN), which has lower reactivity than the biomass tar, in order to make the effect of Cu/Ni much clearer. The characterizations with XRD, STEM-EDX, H2 chemisorption, and FIIR of CO adsorption suggest that the obtained Ni-Cu alloy nanoparticles had uniform composition in the range of Cu/Ni = 0.1–1; the particle size was decreased with the increase of Cu/Ni ratio (ca. 5–7 nm), and Cu tended to be enriched on the particle surface. The HTlcs-derived Ni-Cu alloy catalysts showed a volcano-type dependence of activity on the alloy composition; the highest reforming activity and lower yields of byproducts including benzene, naphthalene, and coke were obtained at Cu/Ni = 0.25. The kinetic study indicates that 1-MN was strongly adsorbed on both the Ni and Ni-Cu catalysts; in contrast, the adsorption of steam was promoted by the alloying of Ni with Cu even in the presence of strongly adsorbed 1-MN. The property of stronger adsorption of steam can be connected to higher reforming activity and lower coke deposition through the dissociative adsorption of steam to supply more adsorbed oxygen species, which enhance the gasification of carbonaceous species.

The influence of the preparation methods of Co-Al layered double hydroxides (LDHs) on the structural and catalytic properties of Co-Al mixed oxides for benzene total oxidation was investigated. Various Co-Al LDHs were synthesized via constant pH precipitation, decreasing pH precipitation, and urea homogeneous precipitation. The synthesized samples were characterized by using N2 physical adsorption, ICP, XRD, TG–DTA, SEM, and H2-TPR. The characterization results showed that calcination of Co-Al LDHs gave rise to Co-Al mixed oxides consisting of Co(Co, Al)2O4 spinel as the main phase, which showed relatively small crystallite size and high specific surface area, i.e., ~12 nm, 90–100 m2 g cat −1 . The highest catalytic activity was obtained on the Co-Al mixed oxide prepared by decreasing pH precipitation, followed by that prepared by constant pH precipitation, while the Co-Al mixed oxide prepared by urea homogeneous precipitation was much less active. The activity difference can be related to the different reducibility of Co3+ species in Co(Co, Al)2O4 spinel.

Steam reforming of tar model compounds (benzene, toluene and phenol) was carried out using Ni–Fe/Mg/Al catalysts prepared by calcination and reduction of hydrotalcite-like precursor. Ni–Fe/Mg/Al (Fe/Ni = 0.25) catalyst showed higher activity (∼twice conversion rate based on catalyst weight) and better resistence to carbon deposition (∼one order smaller amount of deposited carbon) than Ni/Mg/Al. The difference in the weight-based rate and carbon deposition amount between catalysts with and without Fe was large when benzene or toluene was used as a substrate and high steam/carbon (S/C) ratio was applied. On the other hand, when phenol was used as a substrate, relatively large amount of carbon derived from decomposition of phenol was deposited on Ni–Fe/Mg/Al catalyst even with high (3.8) S/C ratio. The catalyst loses some activity for steam reforming of toluene when treated with phenol (untreated catalyst: ∼80% conversion of toluene (rate 51 μmol g −1 -cat s −1 ); treated catalyst ∼60% (rate 38 μmol g −1 -cat s −1 )), probably because of the deposited carbon from phenol. Kinetic studies and O 2 - or H 2 O-TPO studies showed that phenol was strongly adsorbed on Fe site as well as Ni site, and the adsorbed phenol could be converted into carbonaceous species under the reaction conditions. On the other hand, the adsorbed phenol on Ni site underwent steam reforming, and the reaction was promoted by Fe.

A series of Co-Al mixed oxides were prepared by co-precipitation method via Co-Al layered double hydroxides (LDHs) as precursors. The influence of chemical compositions of Co-Al LDHs on the structural and physicochemical properties of Co-Al mixed oxides as well as their catalytic performance for benzene total oxidation was investigated. The samples were characterized by using ICP, N 2 physical adsorption, XRD, TG-DTA, SEM, TEM, Raman, H 2 -TPR, and XPS techniques. The characterization results showed that calcination of Co-Al LDHs gave rise to Co(Co, Al) 2 O 4 spinel-like mixed oxide as the main phase. The crystallite size of Co(Co, Al) 2 O 4 spinel (6 ∼ 19 nm) decreased with decreasing the Co/Al molar ratio, suggesting the inhibition of crystal growth by the incorporation of Al 3+ ions in the spinel phase. A drastic change in the state of Co-Al mixed oxide occurred at Co/Al = 6, as indicated by H 2 -TPR and XPS. In benzene total oxidation, the activity of Co-Al mixed oxide increased with increasing the Co/Al molar ratio, with the highest activity at Co/Al = 5; further increase in the Co/Al molar ratio to 6 led to significant decrease in the activity, properly caused by the change of surface state of mixed oxide. The 50 h long-term stability test revealed that the optimized Co-Al mixed oxide was stable for the total oxidation of benzene.

Catalytic gasification of the oil-extracted residue biomass of Botryococcus braunii was demonstrated in a laboratory-scale continuous feeding dual bed reactor. Steam gasification at 1023 K over Ni-Fe/Mg/Al catalyst can completely reform tar derived from pyrolysis of the residue biomass into C1 gases and hydrogen, and has achieved 91%-C conversion to gaseous product (CO+CO2+CH4). Composition of product gas has higher contents of CO and H2 with their ratio (H2/CO) of around 2.4 which is slightly H2-rich syngas. Maximum hydrogen yield of 74.7 mmol g-biomass(-1) obtained in this work is much higher than that from gasification of other algal biomass reported in literature. The residue biomass of B. braunii can be a superior renewable source of syngas or hydrogen.

Various Cu catalysts were prepared by the calcination and reduction of Cu-containing layered double hydroxides (LDHs) including Cu–Al LDHs, Cu–Mg–Al LDHs, Cu–Zn–Al LDHs, and Cu–Zn–Cr LDHs. The catalysts were characterized by using ICP, N 2 physisorption, TG, SEM, XRD, H 2 -TPR, and N 2 O chemisorption, and tested for the water-gas shift (WGS) reaction at 453–623 K. The characterization results reveal the formation of LDHs on the as-synthesized precursors. Upon calcination and reduction, highly dispersed Cu nanoparticles, particularly for Cu/MgO/Al 2 O 3 , were formed. The Cu 0 surface area and Cu dispersion was found to be Cu/MgO/Al 2 O 3 > Cu/Al 2 O 3 > Cu/ZnO/Al 2 O 3 > Cu/ZnO/Cr 2 O 3 . The activity of the LDHs-derived Cu catalysts for WGS decreased in the order of Cu/MgO/Al 2 O 3 ∼ Cu/ZnO/Al 2 O 3 > Cu/ZnO/Cr 2 O 3 > Cu/Al 2 O 3 . The high activity of Cu/MgO/Al 2 O 3 was attributed to its high Cu 0 surface area and Cu dispersion, while the interaction between metallic Cu and ZnO on Cu/ZnO/Al 2 O 3 might be responsible for the WGS activity. Interestingly, the highly dispersed Cu metal particles on the Cu/MgO/Al 2 O 3 catalyst seemed stable during the WGS reaction.

Ni–Cu/Mg/Al bimetallic catalysts were prepared by the calcination and reduction of hydrotalcite-like compounds containing Ni2+, Cu2+, Mg2+, and Al3+, and tested for the steam reforming of tar derived from the pyrolysis of biomass at low temperature. The characterizations with XRD, STEM-EDX, and H2 chemisorption confirmed the formation of Ni–Cu alloy particles. The Ni–Cu/Mg/Al bimetallic catalyst with the optimum composition of Cu/Ni = 0.25 exhibited much higher catalytic performance than the corresponding monometallic Ni/Mg/Al and Cu/Mg/Al catalysts in the steam reforming of tar in terms of activity and coke resistance. The catalyst gave almost total conversion of tar even at temperature as low as 823 K. This high performance was related to the higher metal dispersion, larger amount of surface active sites, higher oxygen affinity, and surface modification caused by the formation of small Ni–Cu alloy particles. In addition, the Ni–Cu/Mg/Al catalyst showed better long-term stability than the Ni/Mg/Al catalyst. No obvious aggregation and structural change of the Ni–Cu alloy particles were observed. The coke deposition on the Ni–Cu/Mg/Al catalyst was approximately ten times smaller than that on the Ni/Mg/Al catalyst, indicating good coke-resistance of the Ni–Cu alloy particles.

The Co/Mg/Al catalysts were prepared from the hydrotalcite-like compounds containing Co, Mg and Al, and applied to the steam gasification of biomass. It is found that the Co/Mg/Al (10/40/50) catalyst exhibited much higher activity and resistance to coke deposition than Co/α-Al 2 O 3 , Co/Al, Co/Mg and Ni/Mg/Al (9/66/25) catalysts. The catalyst characterization using BET, TPR, TPO, XRD, H 2 adsorption, and TEM indicates that the Co/Mg/Al (10/40/50) catalyst after the reduction has a nanocomposite structure of Co metal particles (∼14 nm) and oxide particles (∼16 nm) of MgAl 2 O 4 -based solid solution. On the other hand, according to the catalyst characterization after the catalytic use and regeneration, the structural change of MgAl 2 O 4 -based solid solution to MgO-based solid solution can be a cause of the decrease of the catalytic activity.

A series of copper ferrite-based catalysts were prepared by the co-precipitation method using KOH, K 2 CO 3 , Na 2 CO 3 , NaOH, and NaHCO 3 as the precipitants and their physicochemical properties were investigated by N 2 -physisorption, SEM, XRD, FT-IR, Raman, H 2 -TPR, N 2 O decomposition, and CO 2 -TPD. The characterization results indicated that the utilization of KOH as precipitant was favorable for the formation of copper ferrite, which exhibited smaller crystalline and higher reducibility. The catalytic test in the water–gas shift reaction (WGSR) revealed that the sample prepared with the KOH as precipitant exhibited higher activity and thermal stability than the other samples. It was suggested that higher Cu dispersion, larger amount of surface copper atoms, weak basic sites, and strong interaction between copper and iron oxides resulting from the copper ferrite were responsible for the high catalytic performance.

A series of CuO/ZrO 2 catalysts with different Cu loadings (4.1, 6.1 and 8.4 wt.%) were synthesized by a deposition-precipitation method and evaluated with the water–gas shift (WGS) reaction. In order to distinguish the different supported copper oxide species, (NH 4 ) 2 CO 3 -leaching process was conducted on the three CuO/ZrO 2 catalysts. The parent and leached catalysts were characterized by ICP-OES, XPS, XRD, N 2 -physisorption, N 2 O titration, UV–Vis DRS, H 2 -TPR and CO-TPR. The results reveal that three types of copper oxide species are present on the parent CuO/ZrO 2 catalysts: (α) highly dispersed CuO that is weakly bound with ZrO 2 ; (β) strongly bound Cu-[O]-Zr species, which can not be leached by (NH 4 ) 2 CO 3 solution and is possibly associated with the surface oxygen vacancy of ZrO 2 ; (γ) crystalline CuO. The XRD and TEM results of the freshly reduced catalysts disclose that the three types of CuO species are transformed into their corresponding metallic states after the H 2 -pretreatment. It is found that the reaction rate correlates well with the amount of Cu-[O]-Zr species, indicating the metallic Cu derived from this species should be the catalytically active copper species for the WGS reaction. Moreover, CO-TPR results disclose that the Cu-[O]-Zr species play a significant role in promoting the reactivity of the surface hydroxyl groups, as is thought to be responsible for the high WGS activity of the CuO/ZrO 2 catalysts.

The performances of Ni–Co/Al 2 O 3 catalysts with the optimum composition were much higher than the corresponding monometallic Ni and Co catalysts in terms of the catalytic activity, the resistance to coke formation and catalyst life in the steam reforming of biomass tar. This behavior can be related to the formation of the Ni–Co solid solution alloys indicated from the characterization with XRD, TPR, TEM, H 2 adsorption and EXAFS.

The addition of hydrogen to the reactant gas for the toluene steam reforming enhanced the stability and activity of Co-Fe/α-Al 2 O 3 (Fe/Co = 0.25), which is due to the suppression of the oxidation of the bcc Co-Fe alloy phase as the catalytically active species. It is characteristic that the adsorption of hydrogen on Co-Fe/α-Al 2 O 3 was much stronger than that on Co/α-Al 2 O 3 , suggesting that the coverage of adsorbed hydrogen species can be rather high under the reaction conditions. The kinetics analysis gave almost first reaction order with respect to toluene and higher reactivity of toluene than benzene indicate that the activated adsorption of toluene can proceed via its methyl group and it can be assisted by adsorbed hydrogen species at the bcc Co-Fe alloy surface.

Co catalyst supported on BaAl12O19 (BA) showed higher activity in the steam reforming of tar from the pyrolysis of biomass than those supported on Al2O3, ZrO2, SiO2, MgO, and TiO2. Characterization results indicate that the Co metal particles supported on BA had high dispersion, although the surface area of Co/BA was small. High dispersion of Co metal particles on BA can account for the high steam reforming activity, and this high dispersion is related to the strong basicity of the BA surface. Strong basicity of BA and high dispersion of Co metal particles on BA are connected to high H2O reactivity to form H2, probably at the interface between Co metal and BA. In addition, the Co/BA catalyst exhibited higher reusability through the coke combustion and the subsequent reduction treatment than the Co/Al2O3 catalyst. This is attributed to the suppression of the solid reaction between the oxidized Co and BA.

We investigated the performance of Ni + MnOx/Al2O3 catalysts in the steam reforming of tar from the pyrolysis of cedar wood. Performance of Ni + MnOx/Al2O3 catalyst with optimum composition was much higher than those of the corresponding monometallic Ni and MnOx catalysts. This tendency is also supported by the activity test in the steam reforming of toluene as a model compound of tar. Based on the catalyst characterization results, the surface of Ni metal particles was partially covered with MnOx, and the interaction between Ni metal and MnOx can play an important role on the enhancement of the catalytic activity and the suppression of coke deposition in the steam reforming of tar. Excess MnOx addition decreased the catalytic activity by decreasing the number of the surface Ni atoms.

Performance of Co–Fe/Al 2 O 3 catalysts with the optimum composition (Fe/Co = 0.25) was much higher than corresponding monometallic Co and Fe catalysts in the steam reforming of tar from the pyrolysis of cedar wood in terms of the catalytic activity and the suppression of coke deposition. According to the catalyst characterization, the fcc and bcc Co–Fe alloys were formed by H 2 reduction on the Co–Fe/Al 2 O 3 catalyst. In the steam reforming of toluene, the addition of H 2 to the reactant gas enhanced the activity of Co–Fe/Al 2 O 3 remarkably. Without H 2 addition, bcc Co–Fe alloy particles were oxidized and this is connected to the deactivation. With H 2 addition, the bcc Co–Fe alloy with an appropriate composition is maintained in metallic state and it contribute to high activity in the steam reforming of toluene.

Nickel catalysts are effective for the steam reforming of tar derived from biomass pyrolysis, but the improvement is needed in terms of activity, stability, suppression of coke deposition and aggregation, and regeneration. Our recent development of Ni-based catalysts for the steam reforming of tar is reviewed including the modification with CeO2 (or MnO), trace Pt, and MgO. The role of additives such as CeO2, MnO, Pt, and MgO is also discussed.

Nickel is an effective component for the steam reforming of methane in terms of the catalytic activity and the catalyst cost. When Ni catalysts are applied to dry reforming, oxidative reforming, and catalytic partial oxidation, it is necessary to add the properties of high resistance to oxidation, hot spot formation, and coke deposition, to the Ni catalysts. An efficient method for giving these properties while considering the catalyst cost is the modification of Ni metal particles with small amounts of noble metals. An important point is that preparation methods can affect the structure of noble metal–Ni bimetallic particles, which is connected to the catalytic performances. The additive effects of noble metals on the catalytic performances are summarized in terms of activity, suppression of Ni oxidation, carbon formation, self-activation, and sustainability in the daily startup and shutdown operations.

The Ni/Mg/Al catalysts were prepared from the calcination and reduction of hydrotalcite-like compounds containing Ni, Mg and Al, and applied to the steam reforming of tar from pyrolysis of biomass. The dependence of the composition and reduction pretreatment conditions on the catalytic performance was investigated. It is found that the Ni/Mg/Al catalyst with optimized composition of Ni/Mg/Al = 9/66/25 exhibited much higher activity, resistance to coke deposition, and stability than Al 2 O 3 - and MgO-supported Ni catalysts. The catalyst characterization using XRD, TPR, N 2 and H 2 adsorption, and TEM indicates that the Ni/Mg/Al catalyst after the reduction has a nanocomposite structure of Ni metal particles (about 8.5 nm) and Mg(Ni, Al)O particles (about 11.5 nm). Even after the catalytic use, the nanocomposite structure was maintained. High performance of the Ni/Mg/Al catalyst including the suppression of the aggregation of the metal particles can be caused by the nanocomposite structure.

Catalytic performance of Ni-Fe/Al2O3 catalysts with the optimum composition was much higher than corresponding monometallic Ni and Fe catalysts in the steam reforming of tar from the pyrolysis of cedar wood. According to the catalyst characterization, the Ni-Fe alloys were formed and the Fe atoms on the alloys tend to be enriched on the surface, and it was suggested that the structure was maintained mainly during the reaction. The surface Fe atoms supply oxygen species, enhancing the reaction of tar and suppressing the coke formation. Excess Fe addition decreased the catalytic activity by decreasing the surface Ni atoms.

Trace amounts of MgO were doped on Cu/ZnO/Al 2 O 3 catalysts with the Cu/Zn/Al molar ratio of 45/45/10 and tested for the water–gas shift (WGS) reaction. A mixture of Zn(Cu)–Al hydrotalcite (HT) and Cu/Zn aurichalcite was prepared by co-precipitation ( cp ) of the metal nitrates and calcined at 300 °C to form the catalyst precursor. When the precursor was dispersed in an aqueous solution of Mg(II) nitrate, HT was reconstituted by the “memory effect.” During this procedure, the catalyst particle surface was modified by MgO-doping, leading to a high sustainability. Contrarily, cp -Mg/Cu/Zn/Al prepared by Mg 2+ , Cu 2+ , Zn 2+ and Al 3+ co-precipitation as a control exhibited high activity but low sustainability. Mg 2+ ions were enriched in the surface layer of m -Mg–Cu/Zn/Al, whereas Mg 2+ ions were homogeneously distributed throughout the particles of cp -Mg/Cu/Zn/Al. CuO particles were significantly sintered on the m -catalyst during the dispersion, whereas CuO particles were highly dispersed on the cp -catalyst. However, the m -catalyst was more sustainable against sintering than the cp -catalyst. Judging from TOF, the surface doping of MgO more efficiently enhanced an intrinsic activity of the m -catalyst than the cp -catalyst. Trace amounts of MgO on the catalyst surface were enough to enhance both activity and sustainability of the m -catalyst by accelerating the reduction–oxidation between Cu 0 and Cu + and by suppressing Cu 0 (or Cu + ) oxidation to Cu 2+ .

Trace amounts of Pt- and Ru-doped Ni/Mg(Al)O catalysts were prepared by a citrate method and tested in the oxidative reforming of C 3 H 8 under daily start-up and shut-down (DSS) operation. The activity and the sustainability of the catalysts were compared with those of the Pt- and Ru-doped Ni/Mg(Al)O catalysts derived from hydrotalcite (HT) precursor. The DSS operation of C 3 H 8 reforming was carried out with O 2 gas or O 2 /H 2 O mixed gas between 200 °C and 600 °C or 700 °C under air purging conditions. The catalysts underwent steaming treatment with H 2 /H 2 O mixed gas at 900 °C for 10 h. This allowed us to test the effect of Ni sintering on the catalyst deactivation. Coking was significantly suppressed on both HT- and citrate-derived Ni catalysts. Although both preparations produced highly dispersed Ni particles on the catalysts, the HT-derived catalysts exhibited more finely dispersed Ni particles, resulting in higher activity values than those of the citrate-derived catalysts. The regenerative activity due to redispersion of sintered Ni particles was enhanced over the HT-derived catalysts compared with the activity over citrate-derived catalysts. Although a clear redispersion of Ni particles was not observed in the oxidative reforming, i.e., in the absence of steam, the size decrease in Ni particles was more significant over the HT-derived catalysts than over the citrate-derived catalysts. The Mg(Al)O periclase structure derived from Mg-Al HT likely plays an important role in the regenerative activity of Pt- and Ru-Ni/Mg(Al)O catalysts. Pt-doping was more effective than Ru for the catalyst sustainability in the oxidative reforming of C 3 H 8 .

Ni/[Mg x Al]O ( x = 3.5, 1.5 and 0.5) doped with trace amounts of Pt were prepared from Mg–Al layered double hydroxides (LDHs) aiming the “green” preparations of “intelligent” reforming catalysts. Commercial Mg–Al LDHs were used as raw materials. The LDHs were calcined and impregnated with Ni(II) and Pt(IV) nitrates at room temperature. The preparative conditions were optimized to produce an effective catalyst for the daily start-up and shut-down steam reforming of methane. The catalysts exhibited the “intelligent” properties, i.e., self-activation and self-regenerative activity. We conclude that well crystallized Mg(Al)O periclase played an important role in the “intelligent” properties of the Pt/Ni/[Mg x Al]O catalysts; the periclase acted as an effective Ni reservoir for a reversible reduction–oxidation movement of Ni ions between the outside and the inside of the Mg(Al)O periclase crystals. Surface Ni 0 was oxidized to Ni 2+ by steam and incorporated into Mg(Ni 2+ ,Al)O periclase, whereas the Ni 2+ ions in the periclase were reduced to Ni 0 by the hydrogen spillover forming small Ni 0 particles on the catalyst surface.

“Green” preparation of “intelligent” catalysts for daily start-up and shut-down steam reforming of CH 4 for the reformer of the PEFCs has been investigated; trace Pt-doped Ni/[Mg x Al]O ( x = 0.5, 1.3 and 3.5) catalysts were prepared starting from commercial Mg x –Al hydrotalcites (HTs) by adopting a “memory effect” of HT. The Mg x –Al HTs were calcined to the mixed oxides, i.e., [Mg x Al]O, and were sequentially impregnated with aqueous solutions of Ni(II) nitrates and Pt(IV) nitrates. When [Mg 3.5 Al] HT was calcined to [Mg 3.5 Al]O at 850 °C, well grown Mg(Al)O periclase structure was formed. After impregnating [Mg 3.5 Al]O powders in Ni(II) nitrate solution at 80 °C for 2 h, 10 wt% Ni was completely incorporated by reconstituting Mg(Ni)–Al HT due to the “memory effect”, resulting in a high and sustainable activity due to the formation of self-regenerative Ni(-Pt) particles after 0.05 wt% Pt doping. The catalyst exhibited “intelligent” properties, i.e., self-activation and self-regenerative activity; the finely dispersed Ni(-Pt) particles were effectively self-regenerated via a reversible reduction–oxidation between Ni 0 and Ni 2+ on/in Mg(Ni,Al)O periclase. An increased Ni loading to 16 wt% on [Mg 3.5 Al]O produced Ni(OH) 2 separately from the Mg(Ni,Al)O lattice, leading to the formation of non self-regenerative Ni(-Pt) particles even after 0.1 wt% Pt doping. We conclude that the well grown Mg(Ni,Al)O periclase structure acts as an effective Ni reservoir, through which Ni(-Pt) particles were self-redispersed via oxidative Ni incorporation and reductive Ni release assisted by steam and hydrogen spillover, respectively.

Trace amount of Ru-doped Ni/Mg(Al)O catalyst was prepared from hydrotalcite precursor and was tested in the reforming of propane under daily start-up and shut-down (DSS) operation. Mg(Ni,Al)O periclase derived from the hydrotalcite was dispersed in an aqueous solution of Ru nitrate, followed by calcination and reduction. Finely dispersed Ni–Ru was supported on Mg(Al)O periclase particles. The activity as well as the sustainability in the propane reforming was compared with the commercial Al 2 O 3 -supported Ni and Ru catalysts. The DSS operations of partial oxidation, steam reforming and autothermal reforming were carried out under steam or air purging conditions. The Ru doping suppressed the surface oxidation of Ni particles on the Ni/Mg(Al)O catalyst, resulting in the high activity as well as the high sustainability in all reforming reactions except under steam–air combined purging. The deactivation was effectively suppressed by increasing either reaction temperature or Ru doping even under steam–air combined purging. Ni particles also suffered by sintering, but the sintered Ni particles were redispersed and the activity was sustained during DSS operations. Air-purged partial oxidation was the most effective for the redispersion of the sintered Ni particles. This likely indicates that the finely dispersed Ni particles were continuously regenerated by reversible reduction–oxidation between Ni 0 and Ni 2+ via Mg(Ni)Al periclase assisted by hydrogen spillover from Ru or NiRu alloy.

Doping effects of Pt and Ru on Ni/Mg(Al)O catalysts were compared in daily start-up and shut-down operations of steam reforming of CH 4 . Trace Pt-doped catalyst showed better behavior than trace Ru-doped catalyst; the former was self-activated but the latter was not, although both exhibited self-regenerative activity. Moreover, the former exhibited sustainable activity, although the latter was quickly passivated, in the autothermal reforming of CH 4 . Formation of Pt–Ni alloy on the surface of fine Ni metal particles on the catalysts was suggested by EXAFS analyses. CH 4 was dissociatively activated to form hydrogen on Pt, assisted by adsorbed O or OH species, leading to the self-activation via Ni reduction by hydrogen spillover from Pt. The self-regeneration of the Pt–Ni/Mg(Al)O catalysts can be achieved by the continuous rebirth of active Ni metal species via reversible reduction–oxidation between Ni 0 and Ni 2+ in/on Mg(Ni,Al)O periclase assisted by the hydrogen spillover.

Trace amounts of noble metal were doped on Cu/ZnO/Al2O3 catalysts by adopting “memory effect” of hydrotalcite. Ternary Cu/ZnO/Al2O3 (molar ratio Cu/Zn = 1/1, Al content 0–25 mol%) catalysts were prepared by co-precipitation (cp) from metal nitrates; a mixture of hydrotalcite (Cu,Zn)6Al2(OH)16CO3·4H2O, and aurichalcite (Cu,Zn)5(CO3)2(OH)6, was formed at pH 9 with NaOH as the pH controller. Finally the sample, cp-Cu/Zn/Al(45/45/10) containing mainly aurichalcite together with a small amount of hydrotalcite, was selected as the precursor for the noble metal-doping. Noble metal-doping was conducted by dipping the precursor calcined at 300 °C in aqueous solutions of the noble metal nitrates; hydrotalcite was reconstituted by the “memory effect” and simultaneously noble metals were incorporated. The noble metal-doped samples were calcined at 300 °C and tested for the water–gas shift (WGS) reaction. Among the noble metals, Pt was the most effective for stabilizing the catalytic activity although some deactivation due to Cu sintering took place. An intrinsic promoting effect of Pt was clearly observed by evaluating the turnover frequency of the catalyst. Aurichalcite was indispensable for producing active Cu/ZnO sites, whereas a small amount of hydrotalcite was effective for improving the sustainability of the catalyst by the surface modification. It is likely that hydrogen-spillover from trace Pt to active Cu metal not only enhanced the activity via the reduction–oxidation cycle between Cu0 and Cu+ but also stabilized the active Cu metal species against oxidative sintering during the reaction.

Ternary Cu/ZnO/Al2O3 catalysts have been prepared by homogeneous precipitation (hp) using urea hydrolysis and tested for the water-gas shift reaction. The Cu/Zn ratio was fixed at 1/1, and the effects of the Al addition on the precipitation procedure, the precursor structure and the catalytic activity have been studied. The precipitation proceeded stepwise; Cu(II) nitrate was first hydrolyzed, followed by the hydrolysis of Zn(II) nitrate, but the final compounds consist mainly of aurichalcite. It is likely that amorophous Cu(OH)2 formed first was converted to aurichalcite via a dissolution-reprecipitation mechanism assisted by Zn(II). A significant leaching of Cu took place with increasing Al content during the precipitation at 90 °C. The Cu leaching was effectively suppressed by lowering the temperature to 80 °C, but resulting in a slight decrease in the catalytic activity. In the hp-catalyst precursors, aurichalcite was always observed as the main component, whereas hydrotalcite and malachite appeared with increasing Al component. The catalytic activity increased by the addition of 5 mol% of Al and decreased with further addition of Al. The activity apparently depended on the Cu metal surface area on the catalyst, but the turn over frequency calculated based on the surface Cu metal significantly varied depending on the Al content. Moreover, the intensity of the reduction peak around 225 °C assigned to Cu2+ → Cu+ in the TPR well correlated with the catalytic activity. It is suggested that Cu/Zn bimetallic aurichalcite has an important role as the catalyst precursor and the reduction–oxidation between Cu+ and Cu0 plays in the catalytic mechanism of the shift reaction.

A series of aluminum promoted Cu/CeO2 nanocatalysts with aluminum content in the range of 0–5wt.% were prepared by co-precipitation method and examined with respect to their catalytic performance for the water–gas shift (WGS) reaction. The catalysts were characterized by XRD, BET, H2-TPR and cyclic voltammetry (CV) techniques. The results indicate that catalytic activity increases with the aluminum content at first, but then decreases with the further increase of aluminum content. Hereinto, Cu/CeO2 catalyst doped with 1 wt.% of aluminum shows the highest catalytic activity (CO conversion reaches 84.4% at 200 °C) and thermal stability for WGS reaction. Correlation to the results from above characterization, it is found that the variation of catalytic activity is in very agreement with that of the surface area, the area of peak γ (i.e., the reduction of surface copper oxide (crystalline forms) interacted with surface oxygen vacancies on ceria), and the area of peak C2 and $$\hbox{A}_{1} (\hbox{Cu}^{0}\,\leftrightarrow\,\hbox{Cu}^{2+}$$ in cyclic voltammetry process), respectively. Enough evidence was found for the fact that the metallic copper (Cu0) interacted with surface oxygen vacancies on ceria is the active site for WGS reaction over Cu/CeO2 catalysts.

Ru (0.1–0.5 wt%) loaded Ni/Mg(Al)O catalysts have been prepared by adopting the “memory effect,” i.e., the reconstitution of Mg(Ni)–Al hydrotalcite from the Mg(Ni, Al)O periclase after the heat-treatment, and their catalytic activities have been tested in the partial oxidation of propane. The Ru–Ni0.5/Mg2.5(Al)O catalysts were prepared by dipping Mg2.5(Al,Ni0.5)O periclase derived from Mg2.5(Ni0.5)–Al hydrotalcite in an aqueous solution of Ru(III) nitrate. The reconstitution of hydrotalcite took place by the “memory effect” and was simultaneously accompanied by Ru incorporation in the hydrotalcite layer, leading to the formation of the active Ni–Ru bimetal loaded catalyst after the calcination followed by the reduction. Upon O2 purging at 700 °C during the propane partial oxidation at 600 °C, the Ru–Ni0.5/Mg2.5(Al)O catalyst showed no deactivation, while the Ni0.5/Mg2.5(Al)O catalyst was totally deactivated by the Ni oxidation. Moreover, the Ru–Ni0.5/Mg2.5(Al)O catalysts were self-activated under the reaction conditions without reduction pre-treatment with H2. The activity of the Ru–Ni0.5/Mg2.5(Al)O catalysts was enhanced with increasing the Ru loading after the reduction–oxidation pretreatment. After the treatment, two types of Ni reduction peak were observed in the TPR of the catalysts: the 1st peak observed around 550 °C was weakened, whereas the 2nd peak observed around 750 °C was enhanced, with increasing the Ru loading. The 1st is assigned to non-active Ni2+ ions having square-pyramidal coordination in the outermost layer of the Mg(Al)O structure, while the 2nd is probably of active Ni–Ru bimetallic species composed of finely dispersed Ni metal particles combined with Ru.

Effects of Ru addition on the activity and the sustainability of Ni/Mg(Al)O catalysts were investigated in the daily start-up and shut-down (DSS) operation of the steam reforming of CH 4 . Mg 2.5 (Ni 0.5 )–Al hydrotalcite was prepared by coprecipitation and calcined to form Mg 2.5 (Al,Ni 0.5 )O periclase. When the powders of the periclase were dipped in an aqueous solution of Ru(III) nitrate, the hydrotalcite was reconstituted on the surface of Mg 2.5 (Al,Ni 0.5 )O particles, resulting in the formation of highly dispersed Ru/Ni bimetal supported catalysts after the calcination, followed by the reduction. The addition of Ru on Ni caused a decrease in the reduction temperature of Ni and an increase in the amount of H 2 uptake on the Ni over the catalyst. Formation of Ru–Ni alloy or strong interaction between Ru and Ni was also suggested. When Ru–Ni 0.5 /Mg 2.5 (Al)O catalysts were tested in the DSS-like operation under steam purging, the deactivation due to the oxidation of Ni metal by steam was effectively suppressed by hydrogen spillover. Moreover, only 0.05 wt% of Ru loading was enough to effectively suppress the deactivation during the DSS-like operation.

Ni/Mg(Al)O catalysts doped with trace Ru showed self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. Formation of Ru Ni alloy on the surface of fine Ni metal particles on the catalysts was strongly suggested by EXAFS and TPR measurements. The Ni/Mg(Al)O catalyst was passivated by the oxidative incorporation of Ni0 to Ni2+ in Mg(Ni,Al)O periclase, and trace Ru assisted the regeneration of Ni metal from the Ni2+ by hydrogen spillover. Even notably sintered Ni metal particles on the Ni/Mg(Al)O catalyst by steaming were rapidly redispersed, resulting in the revelation of the high and stable activity during the DSS operation. The self-regeneration of the Ru Ni/Mg(Al)O catalysts can be achieved by the continuous rebirth of active Ni metal species assisted cooperatively by both Ni2+ → Ni0 reduction by hydrogen-spillover via trace Ru metal or Ru Ni alloy and reversible reduction–oxidation between Ni0 and Ni2+ in Mg(Ni,Al)O periclase.

Ni/Mg(Al)O catalyst doped with trace amounts of Rh was tested in steam reforming of methane and the catalytic behavior was compared with the Ru-doped catalyst. Rh-doped Ni/Mg(Al)O catalyst showed a self-activation without any reduction treatment due to the ability for hydrogen production by C H bond cleavage. Such production led to the reduction of lattice Ni2+ in Mg(Al,Ni)O periclase to metallic Ni by hydrogen-spillover. The Rh-doped Ni/Mg(Al)O catalyst showed also a self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. NiRh alloy was formed in the surface layer of metallic Ni particles and Rh was located more profoundly in the particles than Ru in NiRu alloy on the Ru-doped catalyst. The Rh-doping exhibited a prominent performance, whilst the Ru-doping resulted in neither self-activation nor stable activity in the DSS operation. Although the catalyst deactivation took place by the Ni0 oxidation into the lattice Ni2+ in Mg(Al,Ni)O periclase, trace Rh assisted the regeneration of the active metallic Ni from the lattice Ni2+ by hydrogen-spillover. Even metallic Ni particles that had been strongly sintered on the Rh-Ni/Mg(Al)O catalyst by steaming at 900 °C were re-dispersed during the DSS operation, resulting in high and stable activity. The self-regeneration of the Rh-doped Ni/Mg(Al)O catalyst has been achieved by continuous rebirth of active Ni metal particles due to reversible reduction–oxidation between the metallic Ni on the surface and the lattice Ni2+ in Mg(Ni,Al)O periclase, i.e., oxidative incorporation of surface Ni0 into the lattice Ni2+ of Mg(Al,Ni)O and reductive migration of the lattice Ni2+ to the surface Ni0 by hydrogen-spillover.