Hydrogen Temperature-programmed Desorption Research Articles

Effect of microwave calcination on catalytic properties of Pt/MgAl(Sn)Ox catalyst in cyclohexane dehydrogenation to cyclohexene

This paper describes an investigation on catalytic properties of Pt nanoparticles supported on MgAl(Sn)Ox mixed oxide for cyclohexane dehydrogenation to cyclohexene. The MgAl(Sn)Ox supports were synthesized by microwave calcined hydrotalcite-derived precursors, and Pt/MgAl(Sn)Ox catalysts were prepared by an incipient wetness impregnation method. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the microwave calcination changed the interfacial character between Pt and support, and strengthened the interaction between tin and support, and facilitated the high dispersion of Pt nanoparticles presented on the support. These effects resulted in higher activity, stability and cyclohexene selectivity in cyclohexane dehydrogenation to cyclohexene.

Bimetallic Pd–Cu catalysts for selective CO2 hydrogenation to methanol

This paper reports on novel Pd–Cu bimetallic catalysts for selective CO2 hydrogenation to methanol. Strong synergistic effect on promoting methanol formation was observed over amorphous silica supported Pd–Cu bimetallic catalysts when the Pd/(Pd+Cu) atomic ratios lied in the range of 0.25–0.34. The methanol formation rate over Pd(0.25)–Cu/SiO2 was two times higher than the simple sum of those over monometallic Cu and Pd catalysts. The Pd–Cu bimetallic catalysts were characterized by X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed desorption. Detailed characterization results demonstrated the importance of two well-dispersed Pd–Cu alloy particles (PdCu and PdCu3) for the observed methanol promotion over Pd–Cu bimetallic catalysts. Similar bimetallic promotion was also observed for Pd–Cu catalysts supported on uniform mesoporous MCM-41, SBA-15 and MSU-F. Conversion-selectivity profile of the Pd–Cu/SiO2 catalyst suggested that CO2 was a primary carbon source for methanol synthesis at lower CO2 conversion, and byproduct CO contributed at higher CO2 conversion within the conversion range examined.

Hydroconversion of Jatropha Oil to Alternative Fuel over Hierarchical ZSM-5

Hierarchical ZSM-5 catalysts were prepared by desilication with different NaOH concentrations. Their structure and acidity were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption and desorption, ammonia temperature-programmed desorption (NH3-TPD), pyridine Fourier transform infrared (FTIR) spectroscopy, CO chemisorptions, and hydrogen temperature-programmed desorption (H2-TPR). The catalytic conversion of jatropha oil into alternative fuel over the NiMo/hierarchical ZSM-5 catalysts was investigated. The deoxygenation pathways were tuned by controlling the alkaline treatment. The DCO2 reaction was strongly favored by strengthening the support-active phase interaction. The aromatization reaction among C2–C8 olefins led to the increase of organic liquid products, especially the C9–C15 hydrocarbons. In addition, this reaction was significantly improved by partial amorphization of the support but inhibited by the development of intracrystal mesopores. The larger mes...

On the Temperature Programmed Desorption of Hydrogen from Polycrystalline Copper

Temperature programmed hydrogen desorption (H2-TPD) is a versatile tool to characterize metal surfaces in heterogeneous catalysts. We present a systematic H2-TPD study combined with a kinetic analysis of the H2 desorption process from pure polycrystalline copper and alumina supported copper. The results show that, in contrast to typical Cu/ZnO based methanol synthesis catalysts, the alumina support has no measureable influence on the desorption process and that the copper surface in both catalyst can be accurately described by a theoretically deduced mixture of the low index planes Cu(100), Cu(110), and Cu(111).

Effects of adding basic oxides of La and/or Ce to SiO2-supported Co catalysts for ethanol steam reforming

In this study, cobalt catalysts supported on La2O3–CeO2–SiO2 were synthesized by the method of impregnation of the support with aqueous solution of the active phase precursor. These materials were tested in ethanol steam reforming (ESR). The catalysts were characterized by in situ X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), temperature-programmed hydrogen desorption (H2-TPD), temperature-programmed oxidation (O2-TPO), adsorption–desorption of nitrogen (BET) and energy-dispersive X-ray spectroscopy (EDS). After reaction, the spent materials were characterized by XRD, SEM and elemental analysis. The in situ XRD analysis showed the formation of the solid solution CexLa1−xO2−δ and identified cobalt oxide in the spinel structure (Co3O4) and metallic cobalt (Co0). The H2-TPR analysis showed the reduction of cobalt oxide, and it was observed that the peaks of cobalt oxide shifted to lower temperatures as the content of lanthanum increased. The H2-TPD analysis showed that metal surface area and metal dispersion decreased as the percentage of lanthanum oxide in the supports increased. The O2-TPO analysis showed that La2%Ce48%Si50% consumed the most oxygen. The SEM analysis identified filamentous carbon after reaction. The catalysts were active for H2 and CO2 production. The best catalytic performance was shown by Co10%La2%Ce48%Si50%, which gave the highest H2 yield.

The promotion effect of hydrogen spillover on CH4 reforming with CO2 over Rh/MCF catalysts

The mesocellular silica foams (MCF) supported rhodium catalysts, prepared by wetness impregnation method, were tested in CH4 reforming with CO2. Hydrogen temperature-programmed desorption (H2-TPD) analysis showed that hydrogen spillover occurs on MCF loaded with highly dispersed rhodium. The turnover frequency of CH4 (TOFCH4(s−1)) increased with the strength rise of spilt-over hydrogen. The promotion mechanism was investigated by controlled atmosphere 13C and 1H MAS NMR. The spilt-over hydrogen atoms were found to adsorb on the bridged oxygen sites (SiOSi) of MCF and to form surface terminal silanol groups. Meanwhile, in the reforming reaction steps, CH4 dissociation into CH3* and CH3O* decomposition into CH2O* occurred. The results confirmed that hydrogen atoms can spill over from highly dispersed rhodium species to the neighboring bridged oxygen atoms of MCF, which promotes the reaction by facilitating rate determining steps of CH4 dissociation and CHxO*(x=2, 3) intermediates decomposition on metal surface.

Selective Hydrogenation of m-Dinitrobenzene to m-Nitroaniline over Ru-SnOx/Al2O3 Catalyst

Series catalysts of Ru-SnOx/Al2O3 with varying SnOx loading of 0–3 wt% were prepared, and their catalytic activity and selectivity have been discussed and compared for the selective hydrogenation of m-dinitrobenzene (m-DNB) to m-nitroaniline (m-NAN). The Ru-SnOx/Al2O3 catalysts were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and hydrogen temperature-programmed reduction (H2-TPR) and desorption (H2-TPD). Under the modification of SnOx, the reaction activity increased obviously, and the best selectivity to m-NAN reached above 97% at the complete conversion of m-DNB. With the increasing of the SnOx loading, the amount of active hydrogen adsorption on the surface of the catalyst increased according to the H2-TPD analysis, and the electron transferred from Ru to SnOx species, as determined by XPS, inducing an electron-deficient Ru, which is a benefit for the absorption of the nitro group. Therefore, the reaction rate and product selectivity were greatly enhanced. Moreover, the Ru-SnOx/Al2O3 catalyst presented high stability: it could be recycled four times without any loss in activity and selectivity.

Structure–Activity Relationships of NiO on CeO2 Nanorods for the Selective Catalytic Reduction of NO with NH3: Experimental and DFT Studies

CeO2 nanorods impregnated with 2.5 atom % of NiO (NiO/CeO2 nanorods) were successfully synthesized and examined as catalysts for the NH3-selective catalytic reduction (NH3-SCR) of nitric oxide (NO). The catalytic activity of NiO/CeO2 nanorods resulted in up to ∼90% NO conversion at 250 °C, which is superior to that of pure CeO2 nanorods or NiO nanoparticles. Subsequently, extensive studies of the NiO/CeO2-catalyzed reduction of NO were conducted using X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed desorption, and density functional theory periodic calculations. Compared to that of the pure CeO2 nanorods, the results demonstrated that the NiO/CeO2 nanorods resulted in (i) a higher concentration of Ce3+ chemical species, (ii) a larger amount of active Oα, (iii) lower temperature reducibility, (iv) a lower amount of energy required for oxygen vacancy distortion, and (v) a significant adsorption of and strong interaction between NO and NH3 molecules. Our findings therefore elucidated considerable details of the structural properties of the NiO/CeO2 nanorods that were decisive for achieving a highly efficient conversion of NO by the NH3-SCR process at low temperatures.

Co-methanation of Carbon Oxides over Nickel-Based CexZr1–xO2 Catalysts

A new NH3-reduction method was developed for the preparation of Ni-Ce0.12Zr0.88O2 catalysts with different Ni loadings (5, 10, and 15 wt %). The reduction of the catalysts was performed in a tube furnace with NH3 or H-2. The catalysts were characterized using Brunauer-Emmett-Teller, inductively coupled plasma-optical emission spectroscopy, X-ray diffraction, transmission electron microscopy-high-resolution transmission electron microscopy/energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, hydrogen temperature-programmed desorption, and CO pulse chemisorption techniques. The catalytic activity toward the CO and CO2 methanation reaction was investigated. The results showed that the NH3-reduction method lead to a higher active metal reducibility, smaller Ni-0 crystallite size, and higher metal dispersion compared to the H-2-reduction method with 100% CO and 97% CO2 conversions and >= 98% CH4 selectivity at 250 degrees C.

The catalytic performance of Ni2P/Al2O3 catalyst in comparison with Ni/Al2O3 catalyst in dehydrogenation of cyclohexane

The Ni2P/γ-Al2O3 and Ni/Al2O3 catalysts were prepared, characterized, and evaluated for dehydrogenation of cyclohexane. The Ni2P/Al2O3 catalyst exhibited superior activity, selectivity and stability to those of the Ni/Al2O3 catalyst. Characterization results indicate that the small positive charge of Ni and the ensemble effect of P in Ni2P can inhibit sintering of Ni2P and promote reactivity of Ni2P in dehydrogenation of cyclohexane. Moreover, the in situ Fourier transform infrared spectra further reveal that the P-covered Ni(2) sites (Ni3P_P sites) of Ni2P(0001) are responsible for dehydrogenation of cyclohexane. Meanwhile, the hydrogen temperature-programmed desorption experiments indicate that the Ni2P/Al2O3 catalyst contains a large amount of the Ni(2) sites.

Modified Cuo/ZnO/Al<sub>2</sub>O<sub>3</sub> Catalysts for Methanol Synthesis from Co and CO<sub>2</sub> Co-Hydrogenation

A series of CuO-ZnO-Al2O3catalysts modified by different promoter were prepared by co-precipitation or incipient wet impregnation and characterized by X-ray diffraction (XRD), N2physisorption, hydrogen temperature-programmed reduction (H2-TPR) and carbon dioxide temperature-programmed desorption (CO2-TPD). The modified catalysts were tested for methanol synthesis from CO/CO2co-hydrogenation in a fixed bed reactor with feed containing CO, CO2and H2(CO:CO2:H2=1.0:1.08:6.24, volume radio). It is revealed that the catalysts modified by Zr, Mg, Ca has higher activity of methanol synthesis by CO and CO2co-hydrogenation. Especially, the addition of Zr enhances the conversion of total carbon and the selectivity of methanol, which is due to the improved surface area, much more active sites, and the synergistically interaction between CuO and ZnO caused by the addition of Zr promoter.

High performance of Ir-promoted Ni/TiO2 catalyst toward the selective hydrogenation of cinnamaldehyde

The catalytic performance of Ni/TiO2 and Ni–Ir/TiO2 catalysts in the selective hydrogenation of cinnamaldehyde (CAL) has been investigated. The Ni–Ir/TiO2 presented higher activity than the Ni/TiO2. Here, we studied and gave some insights into the interaction between Ni and Ir species and the role of Ir using X-ray diffraction (XRD), transmission electron microscope (TEM), hydrogen temperature-programmed reduction (H2 TPR), hydrogen temperature-programmed desorption (H2 TPD), and X-ray photoelectron spectroscopy (XPS). The size of Ni particles on the Ni–Ir/TiO2 was 10.1nm, smaller than that (12.7nm) on the Ni/TiO2. The reducibility of Ni was improved by addition of a small amount of Ir, as confirmed with the H2 TPR analysis. The Ni–Ir/TiO2 could be reduced at a temperature of 352°C, which is lower than the temperature for Ni/TiO2 (385°C); moreover, a new reduction peak appeared at 240°C due to the stronger interaction of Ni–Ir species, which was certified by XPS analysis. The H2 TPD results indicate that the hydrogen spillover effect may occur in Ni–Ir/TiO2. The electronic structure of the surface Ni atoms was modified upon addition of Ir, resulting in an enhanced activity of the Ni–Ir/TiO2 catalyst, about four times as high as that of the Ni/TiO2 catalyst.

Flower-Like Co-Ni/C Bimetallic Catalysts for the Selective Hydrogenation of o-Chloronitrobenzene

Three dimensional flower-like Co-Ni/C bimetallic catalysts composed of interlaced carbon flakes with highly dispersed metal nanoparticles were synthesized by a facile hydrothermal/solvothermal process followed by a heat treatment in flowing N 2 . The sizes of the metal nanoparticles were from 26 to 4 nm, which became smaller as the Co/Ni molar ratio increased. The catalytic activities for the selective hydrogenation of o -chloronitrobenzene to o -chloroaniline were tested. The conversion of o -chloronitrobenzene over the bimetallic Co-Ni/C catalysts was increased by up to 200% compared with that over a mono-metallic Co/C catalyst, which was due to a synergistic interaction between the Co and Ni species. Hydrogen temperature-programmed desorption results showed that new active sites were formed in the Co 50 Ni 50 /C catalyst due to the formation of a Co-Ni alloy, which gave the improved activity of the Co 50 Ni 50 /C catalyst. 采用简单的水热/溶剂热法, 经后续在氮气气氛中的热处理合成了三维花型 Co-Ni/C 双金属催化剂, 它由交织炭片构成, 金属纳米颗粒高度分散其中. 随着 Co/Ni 摩尔比的增加, 金属颗粒的粒径逐渐从 26 nm 减至 4 nm 左右. 将该催化剂用于邻氯硝基苯选择性加氢制备邻氯苯胺反应, 其催化活性最高为单金属催化活性的 2 倍. 这是由于 Co 和 Ni 物种之间存在协同效应. 氢气程序升温脱附结果显示, Co/Ni 合金的生成使得 Co 50 Ni 50 /C 催化剂产生了新的催化活性位, 因而其活性显著提高. Three dimensional flower-like Co-Ni/C catalysts composed of interlaced nanoflakes with highly dispersed metal nanoparticles gave better activity for the selective hydrogenation of o -chloronitrobenzene because of a synergistic interaction between Co and Ni.

The ethylbenzene hydrogenation over Ni–H3PW12O40/SiO2 in the presence of thiophene

Ni–HPW/SiO2 catalysts with H3PW12O40 (HPW) loading in the range of 0.1–8% were prepared by a modified sol–gel method. The as-prepared catalysts with bimodal pore distribution not only possess relatively large pore and surface area, but exhibit high activity for ethylbenzene hydrogenation even in the presence of thiophene up to 640ppm. It is evident that nickel oxide particles are small and well-dispersed on the surface of these catalysts from X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization. The results of temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of hydrogen and ammonia (H2 and NH3-TPD) also strongly suggest the interaction between Ni component and HPW takes place, and consequently results in remarkable H2 spillover and considerable increase of acidic site concentration of Ni–HPW/SiO2 catalysts. Further, the results of Fourier transform infrared spectroscopy (FT-IR) with pyridine adsorption also show that most of the acid sites are related to Lewis acid and the metal Ni species on the surface of catalysts are therefore prone to be electron-deficient. It is confirmed that HPW plays a critical role in the improvement of sulfur resistance for Ni-based catalysts.

Reduction of Different GeO2 Polymorphs

A combination of volumetric adsorption, thermal desorption and structure-determining methods was used to study and compare the hydrogen reduction behavior of three different GeO2 polymorphs: tetragonal, water-free hexagonal, and water-containing (hydroxylated) commercial hexagonal GeO2. Marked differences in the onset and extent of reduction between the two water-free polymorphs have been observed. Tetragonal GeO2 adsorbs more hydrogen at temperatures T ≤ 673 K and tends to be more easily reducible at low temperatures, but extended Ge metal formation at elevated temperatures is rather suppressed compared to both hexagonal GeO2 phases. Temperature-programmed hydrogen desorption spectra indicate the reduction-induced formation of weakly bonded hydrogen adsorption sites both on hydroxylated and pure hexagonal GeO2. The existence of the most weakly bonded hydrogen is linked to the transformation of initially present hydroxylated species into a tetragonal structure fraction upon annealing at ∼500 K. Thus, analogous forms of hydrogen were not observed on any of the pure (dehydroxylated) structures.

MgAPO-5-supported Pt–Pb-based novel catalyst for the hydrogenation of nitrobenzene to p-aminophenol

Abstract A series of MgAPO-5-supported Pt or bimetallic Pt–Pb catalysts of various Pt loadings were prepared for the hydrogenation of nitrobenzene (NB) to p -aminophenol (PAP). The structural modification and changes in the electronic properties of the catalysts were analyzed using temperature-programmed desorption of hydrogen, high-resolution transmission electron microscopy, and diffuse reflectance infrared Fourier transformation spectroscopy of the adsorbed carbon monoxide. Results show that Pb doping in Pt/MgAPO-5 catalyst decreases the hydrogenation rate of NB and phenylhydroxylamine simultaneously and increases PAP selectivity greatly. A possible reason for the improvement in the PAP selectivity of the Pb–Pt/MgAPO-5 is the increase in electron density of the Pt sites caused by the interaction of Pb and Pt. The decreased rate of NB hydrogenation over the modified Pb–Pt/MgAPO-5 catalyst can be improved considerably by increasing the reaction temperature or hydrogen pressure while maintaining a high PAP selectivity.

Ni–Co–Cu supported on pseudoboehmite-derived Al2O3: Highly efficient catalysts for the hydrogenation of organic functional groups

Ni–Co–Cu catalysts supported on pseudoboehmite-derived Al2O3 were developed for efficient hydrogenation of organic functional groups: CN and NO2 associated with benzene as well as CC in butynediol. Factors such as thermo-treatment of pseudoboehmite, Ni loading, Cu and Co content, and catalyst operating parameters were systematically studied. Among the catalysts, 20%Ni–3%Cu–5%Co/Al2O3 performed the best, showing 100% feed conversion and 84–99.8% selectivity of target products. Techniques such as N2 sorption measurement, scanning electron microscope, hydrogen temperature-programmed reduction and desorption, X-ray photoelectron spectroscopy, and in situ X-ray diffraction were used to characterize the catalysts. The superior performance of the catalyst can be attributed to synergetic interaction among the Ni–Cu–Co constitutes as well as enhancement of Ni2+ reduction and Ni0 dispersion that are resulted due to the co-presence of Cu and Co.

On the interaction of carbon monoxide with ternary Cu/ZnO/Al2O3 catalysts: modeling of dynamic morphological changes and the influence on elementary step kinetics

This paper focuses on gas-phase induced dynamic morphological changes of the catalyst, in particular by carbon monoxide. Those structural changes are studied in terms of hydrogen temperature-programmed desorption (TPD) from carbon monoxide pre-treated surfaces. Modeling the hydrogen TPD from the pre-treated catalyst shows activation of Cu(110) and Cu(100) planes. This is in good agreement with previously shown morphological changes in different gas atmospheres observed from in situ EXAFS and TEM measurements and observed transient maxima of methanol synthesis upon CO pre-treatment which has been reported in the literature. The obtained hydrogen desorption energies for the respective copper surfaces are physically reasonable. This surface heterogeneity is further implemented in a microkinetic model to describe the temperature-programmed surface reaction (TPSR) between carbon monoxide and adsorbed oxygen. It is found that a logarithmic coverage-dependence on adsorbed oxygen is essential for obtaining good agreement between simulation and experiment. For high oxygen loadings the apparent activation energy is essentially constant, which is in good agreement with literature results.

Nickel nanoparticles embedded in the framework of mesoporous TiO 2: Efficient and highly stable catalysts for hydrodechlorination of chlorobenzene

Mesoporous TiO 2-supported metallic Ni catalysts were prepared through a multicomponent assembly approach, where surfactant, titania, and nickel precursor were cooperatively assembled in a one-pot process. With the characterization of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, N 2 physisorption, hydrogen temperature-programmed reduction, and hydrogen temperature-programmed desorption, the resultant Ni nanoparticles were identified to be homogenously embedded within the framework of TiO 2 ranging in size from 1 to 6 nm. The embedment of Ni within the framework of support resulted in larger interface between Ni and support and thus stronger Ni–TiO 2 interaction. During the gas-phase hydrodechlorination of chlorobenzene reaction, the as-prepared 0.23%-Ni/TiO 2-DS delivered turnover frequency up to 1.5 times greater than that associated with the reference Ni/TiO 2 catalyst prepared by conventional incipient-wetness impregnation method. Meanwhile, the as-prepared 0.23%-Ni/TiO 2-DS also exhibited much improved stability for a continuous reaction of 30 h than the reference catalyst. The remarkable enhancement of the catalytic performances was found to depend on the strong metal–support interaction.

The effect of support and synthesis method on the methanation activity of alumina-supported cobalt–ruthenium–lanthana catalysts

The effect of alumina support source as well as preparation method on the methanation activity of cobalt catalysts promoted with lanthanum and ruthenium was investigated. The catalysts were prepared by incipient wetness impregnation using either an acetone and ethanol mix (ratio 4:1 – non-aqueous) or using a dilute nitric acid solution (aqueous) on two commercial aluminas, Puralox SBA200 or Norton type SA6176 alumina. The catalysts were characterised by nitrogen adsorption/desorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption of hydrogen and Fourier transform infrared spectroscopy. Both the support and synthesis method were found to influence the methanation activity with the non-aqueous plus Puralox combination giving the best performance. The activity differences could arise from modification of surface properties leading to variations in cobalt crystallite size and hence improved cobalt metal dispersion.