Monometallic Ni Catalysts Research Articles

Dehydrogenation of Propane to Propylene over Supported Model Ni–Au Catalysts

Hydrogenolysis and dehydrogenation of propane were studied over model nickel–gold catalysts. The supported model Ni–Au catalysts were prepared by depositing Ni and Au onto a planar silica film. Infrared reflection absorption spectroscopic data showed that isolated Ni sites appeared and became dominant on the surface with the addition of Au to Ni. For the conversion of propane in the presence of hydrogen, the dehydrogenation of propane to propylene was observed on the Ni–Au bimetallic catalysts, whereas only hydrogenolysis products were observed on the monometallic Ni catalyst. A correlation was found between the concentration of isolated Ni sites and the catalytic activity for propane dehydrogenation.

Silica-Supported Au–Ni Catalysts for the Dehydrogenation of Propane

Inspired by previous studies on model systems, a series of silica-supported Au–Ni catalysts were prepared and tested for the conversion of propane in the presence of hydrogen. The Au–Ni/SiO2 catalysts were prepared by successive impregnation, i.e. Ni was deposited first followed by Au. TEM/EDX results confirmed the presence of bimetallic Au–Ni nanoparticles. The dehydrogenation of propane to propylene was observed on the Au–Ni bimetallic catalysts, whereas only hydrogenolysis products were observed on the monometallic Ni catalyst. The selectivity to propylene was found to increase monotonically with the Au loading. The results are in good agreement with the results on model catalysts.

황-요오드 열화학 수소 생산 공정에서 니켈-백금 이원금속 촉매를 이용한 요오드화수소 분해 특성

Abstract >> This study was performed to develop a low Pt content catalyst as a catalyst for HI decomposition in S-I process. Bimetallic catalysts added various amounts of Pt on a silica supported Ni catalyst were preparedby impregnation method. HI decomposition was carried out using a fixed bed reactor. As a result, Ni-Pt bimetalliccatalyst showed enhanced catalytic activity compared with each monometallic catalyst. Deactivation of Ni-Pt catalystwas not observed while deactivation of Ni monometallic catalyst was rapidly occurred in HI decomposition. TheHI conversion of Ni-Pt bimetallic catalyst was increased similar to Pt catalyst with increase of the reaction temperature over a temperature range 573K to 773K. From the TG analysis, it was shown that NiI 2 remainedon the Ni(5.0)-Pt(0.5)/SiO 2 catalyst after the HI decomposition reaction was decomposed below 700K. It seems that small amount of Pt in bimetallic catalyst increase the decomposition of NiI 2 generated after the decompositionof HI. Consequently, it was considered that the activity of Ni-Pt bimetallic catalyst was kept during the HI decomposition reaction.

Catalytic performance and characterization of Ni–Co catalysts for the steam reforming of biomass tar to synthesis gas

The performances of Ni–Co/Al2O3 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, H2 adsorption and EXAFS.

Conversion of cellulose to polyols over promoted nickel catalysts

Sorbitol is one of the key platform chemicals that can be applied to several industrial applications, including bio-fuels and hydrogen production. Presently there is no commercial heterogeneous catalytic process to produce sorbitol from cellulose due to the low yield and high cost of noble metals required for the conversion. In this paper we describe an aqueous phase hydrolysis–hydrogenation process to convert cellulose to sorbitol using a cheap Ni based catalyst. Monometallic Ni catalysts showed little activity for the reaction, but with the addition of a small amount of Pt to the Ni catalyst (Ni : Pt = 22 : 1 atom ratio), the activity was greatly enhanced. Results showed that the bimetallic Ni–Pt catalysts supported on mesoporous alumina gave a hexitol (sorbitol + mannitol) yield of 32.4% compared to only 5% with a Ni catalyst. Moreover, Ni–Pt supported on a mesoporous beta zeolite support provided even higher yield of 36.6%. These results were obtained after only 6 hours of run at 200 °C and 50 bar H2 pressure (at room temperature). The presence of a small amount of Pt promotes the protonation of water and hydrogen molecules, which spill over to Ni sites creating in situ acid sites to catalyse hydrolysis of cellulose.

Nickel and nickel–platinum as active and selective catalyst for the maleic anhydride hydrogenation to succinic anhydride

Pt, Ni, Co, Cu and bimetallic Pt–Ni, Pt–Co, Pt–Cu catalysts supported on γ-Al 2O 3 have been studied for the hydrogenation maleic anhydride (MA) to succinic anhydride (SA). X-ray diffraction (XRD) and H 2 temperature programmed reduction TPR studies were performed to characterize the catalysts. The flow reactor studies demonstrated that Pt–Ni bimetallic catalyst is highly active and selective for the hydrogenation of MA. Hydrogenation of maleic anhydride produced mainly succinic anhydride and γ-butyrolactone, and the selectivity toward γ-butyrolactone increased with pressure. Using Al 2O 3 as support, it was possible to obtain the highest reaction rate ever obtained with 90% selectivity to SA at 100% conversion. The process appears to be controlled by H 2 dissociation on nickel and the catalytic activity can be further improved, without loss of selectivity, by adding a very small amount of Pt(0.3) to increase the rate of H 2 dissociation. TPR experiments show high-temperature reduction peaks in monometallic Ni catalysts. When Pt is present, the formation of Pt–Ni compound provokes the shift of the reduction peaks and the appearance of new reduction signals.

Selective conversion of furfural to methylfuran over silica-supported Ni [sbnd]Fe bimetallic catalysts

The conversion of furfural in H 2 over SiO 2-supported Ni and Ni Fe bimetallic catalysts has been investigated at 1 bar in the 210–250 °C temperature range. Over the monometallic Ni catalyst, furfuryl alcohol and furan are primary products resulting from hydrogenation and decarbonylation, respectively. These primary products are further converted in secondary reactions. Furan yields C 4 products (butanal, butanol, and butane) via ring opening, while furfuryl alcohol produces 2-methylfuran via C O hydrogenolysis. By contrast, 2-methylfuran is not produced to a great extent on pure Ni at any level of overall conversion. But, on Fe Ni bimetallic catalysts, the yield of 2-methylfuran greatly increases while the yields of furan and C 4 products decrease. That is, the addition of Fe suppresses the decarbonylation activity of Ni while promoting the C O hydrogenation (at low temperatures) and the C O hydrogenolysis (at high temperatures). DFT analysis of the possible surface species on the mono- and bimetallic surfaces suggests that the differences in selectivity displayed by these catalysts can be attributed to the stability of the η 2-(C,O) surface species, which is higher on the Ni Fe than on pure Ni. As a result, this η 2-(C,O) species can be readily hydrogenated to furfuryl alcohol and subsequently hydrogenolyzed to 2-methylfuran on the bimetallic alloy due to a strong interaction between the carbonyl O and the oxyphilic Fe atoms. Without Fe, on the pure Ni surface, the η 2-(C,O) species can be converted into a surface acyl species, which can be decomposed to produce furan and CO. Detailed XRD and TPR characterization indicate the formation of Fe Ni alloys in all the bimetallic catalysts.

Methane reforming reaction with carbon dioxide over SBA-15 supported Ni–Mo bimetallic catalysts

A series of mesoporous molecular sieves SBA-15 supported Ni–Mo bimetallic catalysts ( xMo1Ni, Ni = 12 wt.%, Mo/Ni atomic ratio = x, x = 0, 0.3, 0.5, 0.7) were prepared using co-impregnation method for carbon dioxide reforming of methane. The catalytic performance of these catalysts was investigated at 800 °C, atmospheric pressure, GHSV of 4000 ml·g cat − 1 ·h − 1 and a V(CH 4)/(CO 2) ratio of 1 without dilute gas. The result indicated that the Ni–Mo bimetallic catalysts had a little lower initial activity compared with Ni monometallic catalyst, but it kept very stable performance under the reaction conditions. In addition, the Ni–Mo bimetallic catalyst with Mo/Ni atomic ratio of 0.5 showed high activity, superior stability and the lowest carbon deposition rate (0.00073g c·g cat − 1 ·h − 1 ) in 600-h time on stream. The catalysts were characterized by power X-ray diffraction, N 2-physisorption, H 2-TPR, CO 2-TPD, TG and TEM. The results indicate that the Ni–Mo bimetallic catalysts have smaller metal particle, higher metal dispersion, stronger basicity, metal–support interaction and Mo 2C species. It is concluded that Mo species in the Ni–Mo bimetallic catalysts play important roles in reducing effectively the amount of carbon deposition, especially the amount of shell-like carbon deposition.

Catalytic performance of manganese-promoted nickel catalysts for the steam reforming of tar from biomass pyrolysis to synthesis gas

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.

Highly Active and Selective Nickel–Platinum Catalyst for the Low Temperature Hydrogenation of Maleic Anhydride to Succinic Anhydride and Synthesis of Succinic Acid at 40 °C

PtNi bimetallic and Ni monometallic catalysts supported on HY–Al2O3, HX–Al2O3, ZSM-5–Al2O3, USY–Al2O3, Beta–Al2O3 and Al2O3 were prepared and evaluated for the hydrogenation of maleic anhydride in the temperature range of 40–150 °C. Results from flow reactor studies showed that supports strongly affected the catalytic properties of different bimetallic and monometallic catalysts. The results showed that the HY–Al2O3 support exhibited the highest activity and selectivity. Using NiPt/Al2O3–HY catalyst and performing the reaction, it was possible to carry out the lowest reaction temperature ever carried at 100% conversion. Adding a small amount of Pt (0.5) to the Ni (5%)/Al2O3–HY catalyst that is effective for increasing the selectivity and activity. We also found that PtNi is an efficient catalyst for the one-pot conversion of maleic acid into succinic acid with 100% conversion at 40 °C. Hydrogenation activity was found to correlate to the extent of PtNi bimetallic bond formation, as characterized by the analysis of XRD and TPR.

Promoting effect of the alloy formation over Ni-Fe/Al2O3 catalysts for the steam reforming of biomass tar to synthesis gas

ABSTRACTThe addition of Fe addition with suitable amount to Ni /Al2O3 catalyst showed higher catalytic performance than corresponding monometallic Ni and Fe catalysts in the steam reforming of tar from the pyrolysis of cedar wood. Characterization of the catalysts indicates the formation of the Ni-Fe alloys and the surface segregation of Fe atoms on the alloys, and it was also suggested that the structure was almost maintained during the reaction. The surface Fe atoms accept oxygen atom from steam and subsequently supply oxygen species to adsorbed carbonaceous species on neighboring surface Ni atoms, which is connected to the promotion of the steam reforming reaction of tar and the suppression of the coke formation.

Catalytic performance and characterization of Ni-Fe catalysts for the steam reforming of tar from biomass pyrolysis to synthesis gas

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.

Correlating extent of Pt–Ni bond formation with low-temperature hydrogenation of benzene and 1,3-butadiene over supported Pt/Ni bimetallic catalysts

Low-temperature hydrogenation of benzene and 1,3-butadiene on supported Pt/Ni catalysts have been used as probe reactions to correlate hydrogenation activity with the extent of Pt–Ni bimetallic bond formation. Pt/Ni bimetallic and Pt and Ni monometallic catalysts were supported on γ-Al 2O 3 using incipient wetness impregnation. Two sets of bimetallic catalysts were synthesized: one set to study the effect of metal atomic ratio and the other to study the effect of impregnation sequence. Fourier transform infrared spectroscopy (FTIR) CO adsorption studies were performed to characterize the surface composition of the bimetallic nanoparticles, and transmission electron microscopy (TEM) was utilized to characterize the particle size distribution. Batch reactor studies with FTIR demonstrated that all bimetallic catalysts outperformed monometallic catalysts for both benzene and 1,3-butadiene hydrogenation. Within the two sets of bimetallic catalysts, it was found that catalysts with a smaller Pt:Ni ratio possessed higher hydrogenation activity and that catalysts synthesized using co-impregnation had greater activity than sequentially impregnated catalysts. Extended X-ray absorption fine structure (EXAFS) measurements were performed in order to verify the extent of Pt–Ni bimetallic bond formation, which was found to correlate with the hydrogenation activity.

MCM-41 supported PdNi catalysts for dry reforming of methane

A series of bimetallic PdNi catalysts supported on mesoporous MCM-41 with different Ni content (Ni/Si ratio of 0.2–0.4) was synthesized. The effect of Pd addition to Ni-containing catalysts as well as the effect of the Ni content on the surface and catalytic properties of the catalysts was studied. The samples were characterized using various techniques, such as energy-dispersive X-ray spectroscopy, N2 adsorption–desorption isotherms, X-ray diffraction, thermogravimetric and differential analyses, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and temperature-programmed reduction. Reforming of methane with carbon dioxide was used as a test reaction. The results indicated that the addition of a small amount of Pd (0.5%) to Ni-containing catalysts leads to formation of small nano-sized, easy reducible NiO particles. Agglomeration of NiO as well as of metallic nickel phase over PdNi samples increased with increasing the Ni content. Formation of filamentous carbon over surface of spent monometallic Ni and bimetallic PdNi catalyst was observed. In spite of filamentous carbon deposition, the catalytic activity and stability of bimetallic PdNi catalysts are higher than those of monometallic Ni one. Within bimetallic system, the PdNi catalyst with Ni/Si ratio of 0.3 revealed the best performance and stability caused by presence of small nickel particles well dispersed on the catalyst surface.

Hydrogen production by aqueous phase reforming of sorbitol using bimetallic Ni–Pt catalysts: metal support interaction

Hydrogen was produced by Aqueous Phase Reforming (APR) of 10% (w/w) sorbitol using mono- and bi-metallic catalysts of Ni and Pt supported on alumina nano-fibre (Alnf), mesoporous ZrO2 and mixed oxides of ceria–zirconia–silica (CZxS) with varying concentration of silica (where x is silica concentration). X-ray diffraction, TEM/EDS and temperature programmed reduction were also carried on these catalysts to study the surface properties. It was observed that co-impregnation of Pt and Ni in atomic ratio 1:12 increased the reducibility of Ni by forming an alloy. However, sequential impregnation of Ni followed by Pt does not form the bi-metallic particles to increase the Ni reducibility. Reduction peak of co-impregnated Ni–Pt/Alnf was found to be 270 °C lower than the sequentially impregnated Pt/Ni/Alnf. The presence of silica at high concentration in CZxS support decreased the reducibility of ceria by forming an amorphous layer on CexZr1−xO2 crystals, which also decreased Ni reducibility. The rate of H2 formation from aqueous phase sorbitol reforming was found to be highest for co-impregnated Ni–Pt catalysts followed by sequentially impregnated Pt/Ni and monometallic Ni catalyst. The H2 activity decreased in the following order of the supports: Alnf > ZrO2 > CZ3S > CZ7S.

Bimetallic Effects for Enhanced Polar Comonomer Enchainment Selectivity in Catalytic Ethylene Polymerization

The synthesis and characterization of the bimetallic 2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato group 10 metal polymerization catalysts {[Ni(CH(3))](2)[1,8-(O)(2)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe(3))(2)} and {[Ni(1-naphthyl)](2)[1,8-(O)(2)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PPh(3))(2)} [FI(2)-Ni(2)(PR(3))(2)] are presented, along with the synthesis and characterization of the mononuclear analogues {Ni(CH(3))[3-(t)Bu-2-(O)C(6)H(3)CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe)(3)} and {Ni(1-naphthyl)[3-(t)Bu-2-(O)C(6)H(3)CH=N(2,6-(i)Pr(2)C(6)H(3))](PPh)(3)} [FI-Ni (PR(3))]. Monometallic Ni catalysts were also prepared by functionalizing one ligation center of the bimetallic ligand with a trimethylsilyl group (TMS), yielding {Ni(CH(3))[1,8-(O)(TMSO)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe(3))} [TMS-FI(2)-Ni(PMe(3))]. The FI(2)-Ni(2) catalysts exhibit significant increases in ethylene homopolymerization activity versus the monometallic analogues, as well as increased branching and methyl branch selectivity, even in the absence of a Ni(cod)(2) cocatalyst. Increasing ethylene concentrations significantly suppress branching and alter branch morphology. FI(2)-Ni(2)-mediated copolymerizations with ethylene + polar-functionalized norbornenes exhibit a 4-fold increase in comonomer incorporation versus FI-Ni, yielding copolymers with up to 10% norbornene copolymer incorporation. FI(2)-Ni(2)-catalyzed copolymerizations with ethylene + methylacrylate or methyl methacrylate incorporate up to 11% acrylate comonomer, while the corresponding mononuclear FI-Ni catalysts incorporate negligible amounts. Furthermore, the FI(2)-Ni(2)-mediated polymerizations exhibit appreciable polar solvent tolerance, turning over in the presence of ethyl ether, acetone, and even water. The mechanism by which the present cooperative effects take place is investigated, as is the nature of the copolymer microstructures produced.

Production of hydrogen and nanofibrous carbon by selective catalytic decomposition of propane

The process of production of highly concentrated CO x -free hydrogen and nanofibrous carbon (NFC) by catalytic propane decomposition on Ni and Ni–Cu catalysts (different in active phase composition) at relatively low temperatures (400–700 °C) was investigated. The bimetallic Ni–Cu catalysts showed significantly higher propane conversion and longer lifetime than monometallic Ni catalyst. The Ni (50 wt.%)–Cu (40 wt.%)/SiO 2 catalyst exhibited the best activity and selectivity at 600 °C. Total hydrogen yield of 60.8 mol H 2/ g cat (during 24 h time on stream) and the total H 2:CH 4 ratio of 8.4 were obtained during propane decomposition under these optimal conditions. The possible reaction scheme of propane decomposition over Ni-based catalysts and the reasons of increasing the selectivity of hydrogen are discussed. Propane decomposition on Ni-based catalysts is accompanied by simultaneous formation of hydrogen and NFC. Carbon nanofibers with stacked-cone structure as well as platelet structure with a wide distribution of carbon nanofiber diameters (10–500 nm) were obtained. These nanofibers were formed by heterogeneous reactions at the temperatures up to 600 °C. At temperatures above 600 °C nanofibers with thin coating of pyrocarbon on their surface were obtained. The branched nanofibers were grown on Ni catalyst. The coiled nanofibers and the carbon nanofiber ropes were grown on Ni–Cu catalysts. This process is proposed to be acceptable for production of CO x -free hydrogen used in proton-exchange membrane fuel cells (PEMFC).

Development of Stable and Highly Active Bimetallic Ni–Au Catalysts Supported on Binary Oxides CrAl3O6 for POM Reaction

The resistance of supported Ni catalysts for carbon deactivation in CH4 partial oxidation (POM) was studied in this work. The 5%Ni/Al2O3 catalyst showed only 18% of CH4 conversion at 900 °C and 23% carbon deposition after 24 h run of POM. Both Au addition and binary support CrAl3O6 use seem to guarantee high activity (100% at 900 °C), selectivity (97% at 900 °C) and high carbon resistance (<1%). Furthermore the gold doped catalysts revealed only the presence of Cα and Cβ whereas the monometallic Ni catalysts showed the presence of graphitic carbon Cγ responsible for catalysts deactivation.

Synthesis and characterization of bimetallic Cu–Ni/ZrO 2 nanocatalysts: H 2 production by oxidative steam reforming of methanol

Cu/ZrO 2, Ni/ZrO 2 and bimetallic Cu–Ni/ZrO 2 catalysts were prepared by deposition–precipitation method to produce hydrogen by oxidative steam reforming of methanol (OSRM) reaction in the range of 250–360 °C. TPR analysis of the Cu–Ni/ZrO 2 catalyst showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addition, this sample showed two reduction peaks, the former peak was attributed to the reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/ZrO 2 catalyst. On the other hand, Cu–Ni/ZrO 2 catalyst exhibited better catalytic activity than the monometallic samples. The difference between them was related to the Cu–Ni nanoparticles present on the former catalyst, as well as the bifunctional role of the bimetallic phase and the support that improve the catalytic activity. All the catalysts showed the same selectivity toward H 2 at the maximum reaction temperature and it was ∼60%. The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the one showed by the monometallic Ni-catalyst.

Hydrocarbon steam reforming on Ni alloys at solid oxide fuel cell operating conditions

We demonstrate that supported Sn/Ni alloy catalyst is more resistant to deactivation via carbon deposition than supported monometallic Ni catalyst in steam reforming of isooctane at moderate steam to carbon ratios, irrespective of the average size of metal particles and the metal loading. The experiments were performed for average diameters of catalytic particles ranging from 30 to 500 nm and for the loading of active material ranging from 15 to 44 wt% with respect to the total mass of catalyst. The steam reforming reactions were performed at conditions that are consistent with typical solid oxide fuel cell (SOFC) operating conditions. DFT calculations show that the reasons for the enhanced carbon-tolerance of Sn/Ni compared to monometallic Ni are high propensity of Sn/Ni to oxidize carbon and lower driving force to form carbon deposits on low-coordinated metal sites.