Gas Phase Hydrogenation Of Benzene Research Articles

Study of catalytic hydrogenation performance for the Pd/CeO2 catalysts

Abstract Pd/CeO2 catalysts with different metallic Pd loading were synthesized by impregnation method. The physicochemical properties of prepared Pd/CeO2 catalysts and corresponding precursors were studied by XRD, XPS, H2-TPD and H2-TPR. Moreover, the catalytic performance of the Pd/CeO2 catalysts was investigated via gas phase benzene hydrogenation reaction at the temperature of 100–200 °C under atmosphere pressure. Results show that the catalytic performance of prepared Pd/CeO2 catalysts is directly related to the metallic Pd content. The amounts of active metallic Pd and adsorbed-desorbed hydrogen species on Pd/CeO2 catalysts increase with the increasing metallic Pd loading from 1.0 to 3.0%, while the numbers of them are slightly reduced on Pd/CeO2(3.5) catalyst. Furthermore, metallic Pd is highly dispersed on the nano-CeO2 supports, therefore, the prepared Pd/CeO2 catalysts present good gas phase benzene catalytic hydrogenation performance. At 200 °C, the benzene conversion over the Pd/CeO2 catalysts with different metallic Pd loading follows the rule: Pd/CeO2(3.0) > Pd/CeO2(3.5) > Pd/CeO2(2.5) > Pd/CeO2(2.0) > Pd/CeO2(1.5) > Pd/CeO2(1.0), corresponding values are 94.3, 96.4, 89.9, 82.8, 72.7, 42.6 and 94.3%. And the cyclohexane selectivity is 100% on all prepared Pd/CeO2 catalysts.

Ni/MIL-120: An efficient metal–organic framework catalyst for hydrogenation of benzene to cyclohexane

A highly thermal stable metal–organic framework (MOF), MIL-120, was employed to incorporate low-cost nickel particles by simple impregnate method to obtain heterogeneous catalyst, Ni/MIL-120. The as-synthesized catalysts were evaluated by gas-phase benzene hydrogenation and exhibited excellent catalytic activities in comparison with classic Ni/Al2O3 catalyst. The X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR) and transmission electron microscopic (TEM) results indicated that Ni species were well dispersed on the MOF matrix and the interaction between the Ni species and the MOF-support was weaker than that between the metal species and Al2O3, which facilitated the catalytic performance of catalyst for benzene hydrogenation.

Preparation of Nanosized RuB with Lower Ru Content Supported on Al<sub>2</sub>O<sub>3</sub> and its Catalytic Activity

The nanosized RuB amorphous alloys with three different ruthenium contents supported on Al2O3 were prepared by means of impregnation, following the chemical reduction with KBH4 solution. The gas-phase benzene hydrogenation was used as a probe reaction to evaluate the catalytic activity of the prepared catalysts. The catalysts were characterized by BET, inductively coupled plasma (ICP), X-ray diffraction (XRD), and transmission electron micrograph (TEM). The experiment results show that the catalytic activity of the three amorphous alloy catalysts goes up first with the increasing of temperature and has a maximum at 443K; when the Ru loading amount is 0.24 %(wt.%) of the catalyst, which is very few, the conversion of benzene on RuB/Al2O3 amorphous alloy catalyst can reach to 99.50% at 443K.

Preparation, characterization and performance of Pd/SiO 2 catalyst for benzene catalytic hydrogenation

Palladium nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium at room temperature. They were characterized by XRD, TEM, EDX, H 2-adsorption, and H 2-TPD. The catalytic properties were evaluated in the gas-phase hydrogenation of benzene in the temperature range of 75–250 °C. Metal particles with a size range of 4.0–25.8 nm were obtained. The metal surface area and hydrogen storage increase with decreasing metal particle size. The H 2-TPD profiles exhibited a main peak appeared at 540 °C with two shoulders at lower (445 °C) and higher (605 °C) temperatures. These peaks were ascribed to strongly adsorbed hydrogen on the surface catalyst. The catalytic activity of the catalysts strongly depends on the metal loading. It increases with decreasing Pd loading. This is ascribed to metal surface area, which increases with decreasing Pd content.

Benzene hydrogenation over Ni–Cu/SiO2 catalysts prepared by aqueous hydrazine reduction

Non conventional nickel (1%) and nickel (1%)–copper (0.2%–0.75%) catalysts supported on silica have been prepared by aqueous hydrazine reduction of nickel acetate at 70°C. They were characterized by TEM, H2-adsorption, H2-TPD and tested in the gas phase hydrogenation of benzene at atmospheric pressure in the temperature range 75°C–230°C. The obtained results show that nickel is in a whisker-like shape or as a film of low density for the Ni/SiO2 and Ni–Cu/SiO2 catalysts respectively. Copper is in the shape of facetted particles in the mono or bimetallic systems with a mean particle size varying from 25 to 100nm. The presence of copper decreased the nickel phase dispersion as well as the conversion whereas it increased carbon deposit in benzene hydrogenation. The results obtained are ascribed to nickel phase shape changes and Ni–Cu interactions. A kinetic reaction mechanism model is proposed. The comparative study of a pair of classical/non-classical Ni/SiO2 catalysts showed much higher surface and catalytic properties of the hydrazine catalyst.

Low temperature activation of Pt/Ni supported MCM-41 catalysts for hydrogenation of benzene

A series of Pt/Ni supported MCM-41 catalysts prepared via classical methods have been investigated. The promotional effect of low activation temperature is shown in comparison to higher temperatures. Surface properties of the catalysts activated at low temperatures were studied using H 2-temperature programmed reduction (H 2-TPR), H 2-chemisorption and H 2-temperature programmed desorption (H 2-TPD) methods while the morphology and size distribution of the particles were obtained using transmission electron microscopy (TEM) analysis. Surface studies showed the promoting effect of Pt on the reduction of Ni species on the support. Total reduction only occurred for the Pt 100 and Pt 90Ni 10 catalysts. Interestingly, it was found that the active phase of the monometallic catalysts were composed of spherical metal particles in the nanosize range, while the bimetallic catalysts showed a combination of spherical and large cubic particles. Tests on the gas phase hydrogenation of benzene show that Pt 50Ni 50 and Pt 90Ni 10 exhibit high activity when compared to Pt 100, though both these catalysts contain lower atomic percentages of Pt. This can be attributed to the anchoring effect of non-reduced Ni 2+ ions that result in well dispersed Pt particles. Kinetic studies were conducted to understand the surface chemical process of the bimetallic catalysts.

Silica supported nanopalladium prepared by hydrazine reduction

Abstract Palladium catalysts (1–10 wt.% Pd) supported on silica were prepared by hydrazine reduction of palladium chloride at room temperature. They were characterized by XRD, TEM, EDX, H2-adsorption, and H2-TPD and tested in the gas phase hydrogenation of benzene in the temperature range 75–250 °C. A conventional catalyst (1 wt.% Pd) obtained by calcination then hydrogen reduction of the same metal precursor was studied for comparison. Metal particles with a size range 6.8–28.4 nm were obtained. Dispersion, hydrogen storage and activity in benzene hydrogenation increased with decreasing particle size. In comparison, the classical catalyst was found much more dispersed (mean particle size of 1.6 nm) and more active (specific rate 1.6–3.7 times higher) than the homolog hydrazine catalyst. However, unexpectedly, turnover frequency (TOF) calculations indicated a greater reactivity of the metal surface atoms for the hydrazine catalyst. It also stored more hydrogen. These contrasting results are discussed in relation with the metal particle morphology.

Benzene adsorption on Mo 2C: A theoretical and experimental study

Continuous gas-phase benzene hydrogenation at 363 K and atmospheric pressure was studied using bulk molybdenum carbide as a catalyst. It was observed that benzene conversion to cyclohexane was initially 100%, dropping to zero after four hours of reaction. After deactivation the catalyst was submitted to a heating program under helium flow from room temperature (RT) up to 1273 K. On-line mass spectrometry showed desorption of benzene and hydrogen suggesting that the deactivation occurred due to strong absorption of benzene on the molybdenum carbide surface. Density Functional Theory (DFT) calculations support this hypothesis showing the adsorption energy of benzene on the molybdenum carbide varies from −377 kJ mol −1 to −636 kJ mol −1 depending on the surface and on the crystal phase. Based on the experimental and theoretical results, a reaction scheme is proposed with the following steps: (i) after synthesis, the molybdenum carbide surface is completely covered by chemisorbed hydrogen; (ii) when the reaction begins, benzene molecules react with the chemisorbed hydrogen via an Eley-Riedeal mechanism, producing cyclohexane and vacant sites on the surface; (iii) other benzene molecules strongly and irreversibly adsorb to these vacant sites, poisoning the surface and thus leading to deactivation of the catalyst.

Study of Ni–Ag/SiO 2 catalysts prepared by reduction in aqueous hydrazine

We have studied bimetallic Ni–Ag (Ni + Ag = 1 wt%) catalysts supported on crystallized silica and prepared by aqueous chemical reduction with hydrazine at 353 K. Two protocols of reduction were used. Prepared catalysts were characterized by means of XRD, TEM, STEM, H 2 chemisorption and H 2-TPD. Their catalytic activity was studied in the gas-phase hydrogenation of benzene. The most important feature of the results obtained is the synergistic effect between Ni and Ag which led to improvement of dispersion and reactivity of nickel in the presence silver for precipitated catalysts. Silver is inactive in the test-reaction. Precipitated bimetallic catalysts give rise to total conversion from 373 K, a temperature at which conversion hardly reaches 30% for the impregnated catalysts. Dispersion and activity pass through a maximum of monotonically decrease with precipitated and impregnated catalysts, respectively. Deactivation was observed for bimetallic catalysts, particularly with precipitated samples. These results could be explained by the mechanism of metal reduction in the hydrazine media. As a result, various Ni–Ag species formed where Ni and Ag phases were separated clusters or interacted as heteroatomic groupings on the carrier surface. These grouping would be responsible of the high performances of the precipitated catalysts.

Nickel niobia interaction in non-classical Ni/Nb 2O 5 catalysts

Non-classical Ni/Nb 2O 5 catalysts [Ni introduced by the simple (SIM) or EDTA-double impregnation (DIM) methods] were prepared by aqueous hydrazine reduction at 353 K. Their structural and surface properties were investigated by XRD, TEM, XPS techniques, and by H 2-TPR, H 2- or O 2-adsorption and isopropanol decomposition measurements. The results obtained confirmed that niobia is a typical SMSI oxide. Indeed, the hydrazine reduced the support and not the supported Ni 2+ ions due to the SMSI effect. Reduction proceeded only in case of a layer of Ni 2+ ions weakly bonded to a sub-layer of Ni 2+ ions strongly attached to the support. This was achieved by stepwise impregnation with the nickel precursor. A very strong nickel–niobia interaction plays a crucial role in the passivation phenomenon of nickel active sites towards hydrogen or in gas phase hydrogenation of benzene. The SMSI effect was in parallel studied on classical catalysts prepared by the SIM or DIM method for comparison.

Study of nickel nanoparticles supported on activated carbon prepared by aqueous hydrazine reduction

Nickel nanoparticles were obtained by the reduction in hydrazine aqueous media of nickel acetate as a precursor supported on activated carbon of high surface area. Classical catalysts using nickel acetate or nitrate were prepared for comparison. The catalysts were characterized by N 2 physisorption, H 2-TPR, H 2-adsorption, TPD, TEM, and XRD, and tested in the gas phase hydrogenation of benzene. Hydrazine catalysts were found much more active in benzene hydrogenation than corresponding classically prepared catalysts. Remarkably, their reactivity is comparable (turn-over frequency of 0.2001–0.2539 s −1 at 393 K) to that of Pt classical catalysts supported on activated carbon in the same conditions. Evidence is given for the existence of the hydrogen spillover effect in benzene hydrogenation, not reported before in the literature. As a result of the hydrogen spillover effect, catalysts performances can be explained by a combination of surface metal atom reactivity, metal–support interaction strength, and specific surface area extent. Maximum effect is observed with hydrazine preparation method, for 1% Ni content and nickel acetate as a precursor. Unexpectedly, it was also found that hydrazine preparation increases the specific area of the catalysts.

Study of nickel catalysts supported on Al 2O 3, SiO 2 or Nb 2O 5 oxides

We have studied nickel classical catalysts supported on Al 2O 3, SiO 2 and Nb 2O 5 oxides, using simple (SIM) or EDTA-double impregnation (DIM) methods. Non-classical catalysts were obtained by pretreatment of the SIM or DIM nickel precursors in aqueous hydrazine at 353 K. The catalysts were characterized by H 2-adsorption, H 2-TPR, isopropanol decomposition and FTIR measurements. They have been tested in the gas phase hydrogenation of benzene. The results obtained show that the support surface acidity order was: SiO 2 < Al 2O 3 < Nb 2O 5. The catalysts exhibited various nickel species due to the existence of various metal–support interaction strengths. As a consequence, the reducibility, surface or hydrogenating properties changed as a function of the nature of the support or method of preparation. The best performances were obtained with the silica support which seemed to interact less with the nickel. The metal–support interactions are highest when niobium oxide is used as the matrix. Ni impregnated on niobia was not active at all, due to very strong metal–support interactions. The interaction of aqueous hydrazine with the catalyst in the reduction conditions was examined. It was shown that hydrazine formed stable complexes with nickel, whereas it adsorbed on the support with a strength depending on the nature of the oxide.

Nanonickel Particles Supported on Silica. Morphology Effects on Their Surface and Hydrogenating Properties

We have studied a whisker-like nickel phase supported on silica and obtained by the reduction of nickel acetate in aqueous hydrazine media. Under H2/300 °C flow, the obtained phase remains stable when the reduction is carried out at 70 °C for 2 h whereas it totally tranforms to spherical-like particles when the reduction is performed at 80 °C for 30 min after a gradual heating from room temperature. It is shown that the whisker-like nickel phase adsorbs and stores more hydrogen than the spherical-like nickel particles. It also exhibits a higher activity in the gas phase hydrogenation of benzene (3-4 times greater). In acetylene hydrogenation, it strongly favors the cylotrimerization process to benzene at the expense of the processes to linear C2-C4hydrocarbons. This work is a direct demonstration of the influence of the metal phase morphology of nickel supported catalysts on their surface and catalytic properties.

Study on catalytic hydrogenation properties and thermal stability of amorphous NiB alloy supported on carbon nanotubes

The supported amorphous NiB/CNTs catalyst was prepared by impregnation, following the chemical reduction with KBH 4 solution. The gas-phase benzene hydrogenation was used as a probe reaction to evaluate the catalytic activity. The amorphous NiB/CNTs catalyst exhibited higher activity than the amorphous NiB/γ-Al 2O 3 catalyst. The difference in activity was due to the better dispersion of active nickel and the electronic interaction between Ni and CNTs on the NiB/CNTs catalyst. The thermal stability of amorphous NiB/CNTs was better than that of NiB/γ-Al 2O 3. Because the unique pore-channel structure of CNTs can protect the active component Ni against agglomeration. Such results were discussed based on various characterizations, including XRD, ICP, XPS, TEM, DSC and CO chemical adsorption.

Nickel containing MCM-41 and AlMCM-41 mesoporous molecular sieves: Characteristics and activity in the hydrogenation of benzene

Pure siliceous and aluminosilicate mesoporous molecular sieves of MCM-41 type have been used as matrices for nickel incorporation (1.7–5%, w/w) via wet impregnation. Moreover, the AlMCM-41-32 material was modified by the cation-exchange method. The properties of the prepared catalysts were studied by means of XRD, XPS, N 2-adsorption, H 2-TPR, H 2-adsorption and TPD. The reaction of gas-phase benzene hydrogenation was carried out on the prepared catalysts. The hydrogen spillover effect in this reaction was also studied using 3% Ni/MCM-41 and 3% Ni/AlMCM-41-32 catalysts diluted by MCM-41 and AlMCM-41-32, respectively. NiSiO 3 and Ni 2O 3 species in the calcined precursor were shown by H 2-TPR and XPS techniques. The presence of metallic aluminium is shown in the Ni/AlMCM-41-32 reduced materials. The reducibility of the catalyst is strongly influenced by the nature of the matrix and the method of preparation. The kinetic study of benzene hydrogenation on 1.7% Ni catalysts demonstrated various partial orders in hydrogen and benzene ascribed to the existence of several surface chemical processes. Investigations on the hydrogen spillover effect showed a maximum of activity for the diluted catalyst. The intensity of hydrogen spillover is strongly decreased in the presence of Al. The kinetic study with the mechanical mixtures suggested changes in the surface reactions due to the contribution of the support to the chemical processes. Moreover, the results strongly indicated that the migration of hydrogen atoms from the metal phase onto the support oxide is assisted by the aromatic hydrocarbon.

Study of nickel catalysts supported on silica of low surface area and prepared by reduction of nickel acetate in aqueous hydrazine

Nickel metal nanoparticles supported on low surface area silica were prepared by reduction of nickel acetate with hydrazine in aqueous medium. The catalysts were characterized by atomic absorption, XRD, TEM, BET surface area, and H 2 chemisorption and TPD. Their hydrogenating properties were evaluated in the gas-phase hydrogenation of benzene. It was found that gas-phase stability and surface properties of the supported nickel particles depended on the nature and temperature of pretreatment. Small nickel particles, in an oxidized or reduced state, were strongly resistant to reducing or oxidizing treatment, respectively. For H 2-treated catalysts, H 2 chemisorption and TPD results suggested the occurrence of hydrogen spillover between the metal nickel phase and the silica. For air and H 2-treated catalysts, hydrogen spillover seemed to involve, in addition, the NiO phase. The activity of the catalysts in benzene hydrogenation also depended on the thermal pretreatment. Precalcined and then reduced catalysts exhibited higher TOFs than nonprecalcined catalysts, suggesting that the presence of the NiO phase may have influenced the hydrogenation process. A comparative study showed that a catalyst prepared by reduction of nickel acetate by hydrazine in aqueous medium stored more hydrogen and was more active in benzene hydrogenation than a conventional catalyst.

Benzene hydrogenation over amorphous NiB/bentonite catalyst and promoting effect of Nd

The supported amorphous NiB/bentonite (Bn) catalyst was prepared by impregnation, following the chemical reduction with KBH 4 solution. The gas-phase benzene hydrogenation was used as a probe reaction to evaluate the catalytic activity. The amorphous NiB/bentonite catalyst exhibited higher activity than the Ni/bentonite catalyst; the difference is due to the formation of amorphous structure and the electronic interaction between Ni and B. Its activity and sulfur resistance were higher than those of the corresponding amorphous NiB/Al 2O 3 catalyst, owing to the better dispersion of active Ni and the stronger acidity over bentonite. Nd in suitable concentration could further enhance the hydrogenation activity and sulfur resistance by improving the surface area of active Ni. Such results were discussed based on various characterizations, including X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature programmed desorption of hydrogen (H 2-TPD), chemisorption and poisoning of carbon disulfide (CS 2).

Gas-Phase Hydrogenation of Benzene to Cyclohexane Over Combustion-Synthesized Ce1-xPtxO2 - δ (x = 0.01, 0.02)

The gas-phase hydrogenation of benzene to cyclohexane over Ce1 - x Pt x O2 - δ (x = 0.01, 0.02) catalyst was investigated in the temperature range 80-200 °C. A 42% conversion of benzene to cyclohexane with 100% specificity was observed at 100 °C over Ce0.98Pt0.02O2 - δ with a catalyst residence time of 1.22 × 104 g s/mol of benzene. The activity of the catalyst was compared with those of Pt metal, combustion-synthesized Pt/α-Al2O3 and Pt/γ-Al2O3. The turnover frequency value of Ce0.98Pt0.02O2 - δ is 0.292, which is an order of magnitude higher than those of the other Pt catalysts investigated. The kinetics of reaction and the deactivation behavior of the catalyst were studied and a regeneration methodology was suggested. The deactivation kinetics and structural evidence from XRD, XPS, TGA and H2 uptake studies suggest that the oxidized Pt in Ce0.98Pt0.02O2 - δ is responsible for the high catalytic activity towards benzene hydrogenation.

Simplified treatment of mass transfer for gas-phase hydrogenation/dehydrogenation of heavy compounds

Using single catalyst pellets (5 mm) 15% Ptγ–Al2O3, we experimentally studied gas-phase benzene hydrogenation at normal pressure by thermocouple measurements of gas flow and the pellet center. Temperature of gas flow was varied in the range of 20 ‡C / 350 ‡C for three molar fractions of benzene vapor (0.1, 0.2, and 0.3) mixed with hydrogen. The ignition/extinction behavior of the flow-pellet temperature rise (maximum values up to 100 ‡C/ 200 dgC) is explained by internal-external mass transport limitations of the reaction rate and reaction reversibility at high pellet temperature. A simplified pseudobinary treatment of both multicomponent intrapellet mass transfer (in bimodal porous media) and multicomponent external mass transfer (under forced convection) is proposed on the basis of the analytical estimation. The validity of the suggested approach is confirmed by comparing the experimental data for benzene hydrogenation with rigorous (multicomponent) and approximated (pseudobinary) calculations obtained by using a mathematical model of a spherically symmetric pellet. The simplified approach appears to be quite accurate for reactions A+nH2=B of hydrogenation (n>0) or dehydrogenation (n<0) of sufficiently heavy compounds, i.e. if D AH ≈D BH >>D AB

Nickel Nanoparticles Supported on Silica of Low Surface Area. Hydrogen Chemisorption and TPD and Catalytic Properties

Nickel metal nanoparticles supported on silica of low surface area (15 m2 g-1) were prepared by reduction of nickel acetate by hydrazine in aqueous medium. Their gas-phase stability and surface properties depended on thermal pre-treatment under H2 or air atmosphere. Small nickel particles (<10 nm), in oxidized or reduced state, are strongly resistant to reductive or oxidative treatment respectively. For H2-treated catalysts, H2 chemisorption and TPD results suggested the occurrence of spillover hydrogen between the metal nickel phase and silica. For air then H2 treated catalysts, hydrogen spillover seemed to involve the NiO phase. The activity of the catalysts in gas-phase benzene hydrogenation also depended on the thermal pre-treatment. Pre-calcined then reduced catalysts exhibited higher TOFs than non pre-calcined catalysts, suggesting that the presence of NiO phase may have influenced the hydrogenation process.