Sequential Impregnation Method Research Articles

Development of Ni catalysts for tar removal by steam gasification of biomass

Catalytic performance of Ni/CeO2/Al2O3 catalysts prepared by a co-impregnation and a sequential impregnation method in steam gasification of real biomass (cedar wood) was investigated. Especially, Ni/CeO2/Al2O3 catalysts prepared by the co-impregnation method exhibited higher performance than Ni/Al2O3 and Ni/CeO2/Al2O3 prepared by the sequential impregnation method, and the catalysts gave lower yields of coke and tar, and higher yields of gaseous products. The Ni/CeO2/Al2O3 catalysts were characterized by thermogravimetric analysis, temperature-programmed reduction with H2, transmission electron microscopy and extended X-ray absorption fine structure, and the results suggested that the interaction between Ni and CeO2 became stronger by the co-impregnation method than that by sequential method. Judging from both results of catalytic performance and catalyst characterization, it is found that the intimate interaction between Ni and CeO2 can play very important role on the steam gasification of biomass.

Promoting effect of the interaction between Ni and CeO2 on steam gasification of biomass

Abstract Catalytic performance of Ni/CeO 2 /Al 2 O 3 catalysts prepared by a co-impregnation method was higher than that of Ni/CeO 2 /Al 2 O 3 by a sequential impregnation method and Ni/Al 2 O 3 in steam gasification of biomass in terms of the yield of coke and tar. Characterization by means of temperature programmed reduction suggests that the intimate interaction between Ni and CeO 2 on the Ni/CeO 2 /Al 2 O 3 by the co-impregnation method can be related to high performance in steam gasification of biomass.

Effect of Na Addition on Catalytic Performance of PtSn/ZSM-5 Catalyst for Propane Dehydrogenation

Abstract PtSnNa/ZSM-5 catalysts with different amounts of Na were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of sodium on the physicochemical properties was studied by means of XRD (X-ray diffraction), IR spectrum of adsorbed pyridine, NH 3-TPD, H 2 chemisorption, TPR (temperature-programmed reduction), etc. The results indicated that the addition of Na had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable concentration of Na could not only reduce the Brönsted acid sites and moderate/strong Lewis acid sites, thus preventing the catalyst from coking and improving the catalytic stability, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus increasing the catalytic activity. It was found that the propene selectivity and yield could reach the maximum, when the Na content was 1.0%. After reaction for 30 h, the propane conversion was still high (36.4%). However, the continuous addition of Na increased the weak Lewis acid sites and promoted the tin species to be reduced to metallic tin. In this instance, the cracking and hydrogenolysis of propane could be carried out easily, which was disadvantageous to the dehydrogenation.

Temperature profile of catalyst bed during oxidative steam reforming of methane over Pt-Ni bimetallic catalysts

The catalyst bed temperature during oxidative reforming of methane (CH 4/H 2O/O 2/Ar = 40/30/20/10) at 1123 K and atmospheric pressure was investigated by infrared thermography over γ-Al 2O 3 supported bimetallic Pt-Ni catalysts prepared by different impregnation methods: co-impregnation and sequential impregnation. The thermographical results clearly demonstrated that the catalyst bed temperature was strongly dependent on the preparation method. The bimetallic catalyst prepared from the sequential impregnation method exhibited much higher resistance to hot spot formation in oxidative reforming of methane. Temperature programmed reduction (TPR) with H 2 revealed that the addition of Pt by a sequential impregnation method greatly promoted the reduction of Ni species; furthermore, infrared spectra of CO adsorption suggests that the surface composition of Pt on the catalyst prepared by the sequential method is much higher than that for the catalyst prepared by the co-impregnation method. The surface enrichment of Pt is responsible for the effective overlap between the combustion and reforming zones, and this can enhance the inhibition of hot spot formation.

Reaction performance and characterization of Co/Al2O3 Fischer–Tropsch catalysts promoted with Pt, Pd and Ru

A series of noble metal (Pt, Ru or Pd) promoted Co/Al2O3 catalysts were prepared by sequential impregnation method. The catalysts were characterized by XRD, TPR, H2-TPD and TPSR techniques, and their catalytic performance in Fischer–Tropsch synthesis was investigated in a fixed-bed reactor. The results of activity measurements show that the addition of small amounts of noble metal greatly improved the activity of the Co/Al2O3 catalyst. TPR experimental results demonstrate that hydrogen spillover from the noble metal to cobalt oxide clusters facilitated the reduction of cobalt oxide and, thus significantly increased the reducibility of Co/Al2O3 catalyst. The presence of noble metal increased the amount of chemisorbed hydrogen and weakened the bond strength of Co–H. TPSR results indicate that CO was adsorbed in a more reactive state on the promoted catalysts.

Strontium as an efficient promoter for supported palladium hydrogenation catalysts

The effect of strontium promotion is studied for a series of supported palladium catalysts such as Pd/zeolite-β, Pd/Al 2O 3, Pd/SiO 2, Pd/hydrotalcite and Pd/MgO. Strontium is found to be an effective promoter for enhancing the metal area, percentage dispersion of the metal and therefore the hydrogenation activity of the different supported palladium catalysts with varying acid/base properties. The effect of addition of Sr and Pd onto the support by simultaneous and sequential impregnation methods is studied besides the effect of Sr/Pd ratio. It is revealed that when sequential addition of Sr and Pd by impregnation is advantageous for alumina, silica, magnesia and hydrotalcite supported palladium catalysts, simultaneous impregnation of Sr and Pd is found to be more effective for zeolite-β supported catalyst. This may be attributed to the microporous nature of the zeolite support that could cause the migration of Sr to its micropores thereby making them non-available for the promotional effect if added first. Addition of strontium is also found to enhance the basicity of the supported palladium catalysts. TPR studies suggest a change in the metal environment upon Sr-promotion indicating an electronic effect responsible for the improvement in the hydrogen adsorption capacity and hydrogenation activity. The promotional effect of Sr on the supported palladium catalysts is explained to be both electronic and physical in nature.

Selective CO oxidation in H 2-rich gas over K 2CO 3-promoted Rh/SiO 2 catalysts: effects of preparation method

The selective CO oxidation in H 2-rich gas over K 2CO 3-promoted Rh/SiO 2 (K 2CO 3-Rh/SiO 2) catalysts was investigated, and the results were compared with those of Rh/SiO 2 catalysts. K 2CO 3-Rh/SiO 2 catalysts were able to realize almost complete removal of CO. The additive effect of K 2CO 3 was dependent on the preparation method and on the K 2CO 3 amounts. K 2CO 3-Rh/SiO 2 catalyst prepared by the sequential impregnation method with molar ratio K/Rh = 3 exhibited high performance. According to the characterization results, the catalyst had highly dispersed Rh metal particles partially covered with K 2CO 3.

Catalyst development for direct heat supply from combustion to reforming in methane reforming with CO 2 and O 2

Pt(0.3)/Ni(10)/Al 2O 3 prepared by a sequential impregnation method exhibited better performance in methane reforming with CO 2 and O 2 in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3)+Ni(10)/Al 2O 3 prepared by the coimpregnation method, Ni(10)/Al 2O 3, Pt(0.3)/Al 2O 3. In methane reforming with CO 2 and O 2 on monometallic Ni(10)/Al 2O 3 catalyst, methane combustion proceeded near the catalyst bed inlet and then the methane reforming proceeded, so a large temperature gradient was observed. However, a flat temperature profile was observed on Pt(0.3)/Ni(10)/Al 2O 3. This suggests that the methane combustion and reforming can proceed simultaneously, and that the heat of combustion is effectively supplied to the reforming reaction. The surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility. This can be an energy efficient process for syngas production, utilizing the combination of catalytic combustion with reforming.

Vapor-Phase Hydrogenation of Crotonaldehyde on Titania-Supported Pt and PtSn SMSI Catalysts

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde have been performed after reduction at low (523 K) and high (773 K) temperatures over Pt/TiO 2 and PtSn/TiO 2 catalysts prepared from the metal precursors tin(II) oxalate and H 2PtCl 6. A sequential impregnation method was used to prepare the bimetallic catalyst, wherein the tin precursor was loaded first. The surface characteristics of both catalysts were evaluated with X-ray photoelectron spectroscopy (XPS) after the reduction treatments. It was shown in this analysis that tin was mainly in an oxidized state in the bimetallic catalyst (about 80%) even after reduction at 773 K. The presence of tin and the increase in the reduction temperature strongly decreased the catalytic activity for toluene hydrogenation, but the opposite effect was observed for crotonaldehyde hydrogenation. After reduction at low temperature, the bimetallic catalyst was more active than the monometallic catalyst, but it was less selective toward hydrogenation of the carbonyl bond to yield the unsaturated alcohol. However, reduction at 773 K yielded a bimetallic catalyst that showed an initial activity five times higher than that of the Pt/TiO 2 catalyst reduced at the same temperature and a high selectivity (around 50%) toward the unsaturated alcohol, which was stable with time on reaction. Furthermore, the catalytic behavior of the bimetallic catalysts was also evaluated after reduction at even higher temperatures. Reduction at 873 K increased the catalytic activity in crotonaldehyde hydrogenation while the selectivity to crotyl alcohol remained at about 50% molar fraction; however, reduction at 973 and 1023 K caused a loss of catalytic performance in terms of both activity and selectivity.

Catalyst Design of Pt-Modified Ni/Al2O3 Catalyst with Flat Temperature Profile in Methane Reforming with CO2 and O2

Pt(0.3)/Ni(10)/Al2O3, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO2 and O2 in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al2O3 prepared by a coimpregnation method, Ni(10)/Al2O3, Pt(0.3)/Al2O3, and Pt(10)/Al2O3. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility.

Increased Sulfur Tolerance of Pt/KL Catalysts Prepared by Vapor-Phase Impregnation and Containing a Tm Promoter

Tm-containing Pt/KL catalysts were prepared by a variety of techniques, including incipient wetness impregnation (IWI), ion exchange (IE), and vapor-phase impregnation (VPI) methods. The Pt morphology resulting from the addition of Tm and Pt sequentially, using the VPI method, was found to yield the greatest enhancement to the aromatization performance of the Pt/KL catalysts studied. The presence of Tm in the sequential VPI Pt/Tm/KL catalyst resulted reproducibly in a catalyst with higher Pt dispersion than that in an unpromoted VPI catalyst, as determined by EXAFS analysis and DRIFTS of adsorbed CO. VPI catalysts give more finely dispersed Pt clusters than either conventional IWI or IE methods. From TPO of poisoned catalysts, Tm was also found to act as a getter for sulfur, so it delays the poisoning of Pt under sulfur-containing feeds, as further evidenced by reaction studies. In addition, the initial activity of the Tm-promoted VPI catalysts was found to be higher than that of the unpromoted Pt/KL VPI catalysts, suggesting that Tm may directly modify Pt or even participate in accelerating the aromatization reaction. The amount and method of incorporation of Tm were found to be critical to the morphology of the Pt clusters and, subsequently, to catalyst performance under sulfur-free and sulfur-poisoned reaction conditions. While the sequential vapor-phase impregnation method with a small amount of Tm (0.15%) yielded a catalyst with improved catalytic properties, some of the other methods such as coimpregnation of Pt and Tm were found to hinder the dispersion of Pt. This may cause the blocking of the L-zeolite channels, as demonstrated by DRIFTS of adsorbed CO, and a higher deactivation rate in the reaction.

The role of lanthanum oxide on Pd-only three-way catalysts prepared by co-impregnation and sequential impregnation methods

The effect of lanthanum oxides on the catalytic performance and the physicochemical properties of Pd‐only three‐way catalysts prepared by co‐impregnation and sequential impregnation methods was studied by using hydrogen chemisorption, BET surface area, X‐ray diffraction and X‐ray photoelectron spectroscopy. It was found that the roles of La closely depended on the order of La introduction in the preparation of the Pd catalysts. Pd–La/Al2O3 prepared by co‐impregnation of La and Pd, kept its superior activity in spite of the significant loss of surface area of the alumina support after thermal aging at 1273 K, indicating that the primary role of La was a Pd stabilizer through the intimate interaction between La and Pd. However, on Pd/La/Al2O3, in which Pd was consecutively impregnated after the impregnation of La, La preferentially interacted with the alumina support as a form of LaxAlyO2, resulting in the stabilization of the alumina support during thermal aging. XPS results indicated that lanthanum oxide suppressed the formation of PdO interacting with alumina during thermal aging. In the case of Pd/La–Ce/Al2O3, the formation of the solid solution of (CexLa1−x)O2 was not strong enough to maintain the high activity and the good textural property after thermal aging.

FTIR study of the oxidation reaction of CO with O2 over bimetallic Pd–Rh/SiO2 catalysts in an oxidized state

CO species adsorbed on the surface of oxidized bimetallic Rh–Pd catalysts, prepared by coimpregnation and sequential impregnation methods, were analyzed in situ by IR spectroscopy, during the reaction of CO with O2 in an oxidizing atmosphere. The results show that the two methods of impregnation lead to the existence of oxidized Rh on the surface of the bimetallic catalyst, however, in the case of the sequential impregnation method, the Pd surface is more reduced than in the case of catalysts prepared by coimpregnation. The simultaneous presence of reduced Pd and oxidized Rh that occurs in the catalysts prepared by sequential impregnation allows the existence of a synergistic effect similar to that proposed in the literature for the Pt–Rh system. The lower degree of oxidation of the Pd in the catalysts prepared by sequential impregnation, is mainly due to the fact that the Pd in these catalysts comes from the organic precursor palladium acetylacetonate, while in the catalysts prepared by coimpregnation, the Pd comes from the precursor PdCl2.

Temperature-programmed surface reaction (TPSR) of pre-adsorbed carbon CO and [formula omitted] synthesis over [formula omitted] catalysts

A series of silica supported ruthenium-caesium catalysts were prepared by sequential impregnation method, and characterized by total surface area determination, and temperature-programmed surface reaction (TPSR) of pre-adsorbed CO with H 2 to form mainly methane. The catalytic behaviour of the catalysts prepared was then studied using CO H 2 synthesis performed in a continuous flow system operating under differential conditions at atmospheric pressure. TPSR experiments revealed that the amount of CO adsorbed estimated from methane formed, decreased with the addition of Cs. This was attributed mainly to site blockage, a purely geometric effect. The main product of the hydrogenation of the pre-adsorbed CO was methane. Peak temperature of methane shifted to higher temperatures with Cs doping indicating that methanation proceeds faster on Ru Al 2O 3 catalyst than on the Cs doped ones. It is suggested that the addition of Cs lead to a decrease in the rate of CO dissociation which is thought to be an essential step in the methanation reaction. Catalytic activity data obtained for the CO H 2 synthesis indicated that the role of Cs as a catalytic modifier is to limit the methanation reaction in preference to hydrocarbon chain growth. It was found that the order of reactivity of pre-adsorbed CO towards hydrogenation to methane in TPSR experiments (transient technique) with respect to Cs loading agreed well with the methanation activity observed in CO H 2 reaction using the continuous flow system (‘steady state’ activity). This good correlation of relative activities obtained by the two sets of experiments demonstrates the validity of comparing TPSR results with those from reaction studies.

CO hydrogenation over zirconia supported iron catalysts promoted with rare earth oxides

Zirconia supported iron catalysts promoted with La 2O 3 and CeO 2, respectively, are prepared by sequential impregnation method. It is shown that the structure, reduction behavior, and the catalytic property for CO hydrogenation of these catalysts are quite different from that of the unpromoted Fe/ZrO 2 sample, and are influenced significantly by the kinds of promoter elements. For the Fe/La/ZrO 2 sample, the catalytic activity is only a little bit higher than that of the Fe/ZrO 2 sample, but light olefins selectivity increases and methane formation is suppressed. For the Fe/Ce/ZrO 2 sample, the catalytic activity is much higher than that of the unpromoted Fe/ZrO 2 sample, while methane formation is suppressed and light olefins selectivity slightly increases. The roles of different rare earth oxide promoters in these catalysts are discussed.

Kinetics of steam-methane reaction on nickel surface

Supported nickel catalysts are promising candidates for dry reforming of methane, but agglomeration of Ni0 and coke deposition hinder the industrial applications. Herein, we report a novel interface-directed synthetic approach to construct distinct metal ensembles by carefully tuning the compositions of the carriers. A Zr-Mn-Zn ternary oxide-supported Ni catalyst, together with the respective binary oxide-supported analogues, was synthesized by adopting a sequential co-precipitation and wetness impregnation method. Combined characterization techniques identify distinct catalyst models, including (i) conventional NiO nanoparticles with different sizes on Zr-Mn and Zr-Zn, and (ii) epitaxially growing NiO ensembles of a few nanometers thickness at the periphery of MnZnOx particles. These catalysts exhibit divergent responses in the catalytic testing, with the ternary oxide system significantly outperforming the binary analogues. The strong electronic interactions between Mn-Ni increase Ni dispersion and the activity while the stability is strengthened upon Zn addition. Both high activity, high selectivity, and remarkable stability are attained upon co-adding Mn and Zn. The interfaces between Ni and Zr-Mn-Zn rather than the physical contacts of individual oxide-supported analogues through mechanical mixing are keys for the outstanding performance.