H2 TPD Research Articles

New insights into the relationship between Cu–Ce interaction and reactive Cu species in CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide in excess hydrogen

A group of CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide (CO-PROX) is designed by constructing different distribution status of Cu species on similar CeO2 support to adjust the Cu–Ce interaction strength. Cycled temperature programmed reduction by hydrogen (H2-TPR) indicates the strength of Cu–Ce interaction can impact the amount and redox properties of surface highly dispersed CuOx and strongly bonded Cu-[Ox]-Ce species, which respectively determines the catalytic performance at low and high temperature. Temperature programed desorption of H2 (H2-TPD) reveals the presence of large amounts of Cu-[Ox]-Ce species can inhibit H2 adsorption and dissociation, which increases the O2 selectivity toward CO oxidation. Moreover, temperature programmed desorption of CO2 (CO2-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) illustrates that H2O and CO2 influences the low-temperature catalytic performance mainly by competitive adsorption with CO on surface highly dispersed reactive Cu+ sites. This work aims to shed light on the underlying Cu–Ce interaction regime, and guide the design of high-performance CuO–CeO2 catalysts in realistic reaction conditions.

Liquid phase hydrodeoxygenation of furfural over laponite supported NiPMoS nanocatalyst: Effect of phosphorus addition and laponite support

Unsupported and laponite supported NiPMoS catalysts were prepared under the hydrothermal method and investigated for liquid-phase hydrodeoxygenation of furfural in a high-pressure batch reactor at 423 ​K − 463 ​K under 20 ​bar H2 pressure. The reaction significantly produced 94% of furfural conversion with 75% yield of 2-MF on NiPMoS catalyst whereas, NiPMoS/Lap catalyst exhibited 28% of 2-MF yield with complete conversion at 463 ​K under 20 ​bar H2 pressure in toluene solvent. The influence of process parameters such as reaction temperature, reactant volume, catalyst compositions, and hydrogen pressure on furfural conversion and product yield was investigated in detail. The high reactivity and synergetic effect of the NiPMoS catalyst are due to added phosphorus, which has a profound influence on the structure of the catalyst, thereby increasing surface acidity, basicity, hydrogen consumption, and a number of MoS2 fringes and the dispersion of MoS2 on the surface of the support. The catalysts were characterized based on HRTEM, H2, CO2, and NH3 TPD, FT–IR, FT–Raman, DRS UV–Vis, XRD, N2–physisorption, and TGA. Recyclability, N2–physisorption, and XRD results confirm the stability and practical applicability of the catalyst for industrial applications.

CeO2 and TiO2 support material effects on NH3 decomposition pathway mechanism over Cu–Zn catalysts

The decomposition of NH3 over Cu–Zn catalysts, supported on ceria and titania, was investigated, producing carbon (di)oxide-free H2. The rate of the H2 formation at the exposed metallic Cu atoms (cumulative turnover frequency) for dispersed Cu–Zn depended strongly on the type of metal oxide support, indicating that the pathway active sites of Cu–Zn nano-catalysts were not identical in quantity. The investigation of the associative desorption process of atomic nitrogen moieties formed by the NH3 scission over Cu–Zn alloy revealed that N2 interface evolution temperature was affected by the nature of substrates. The characterization of the nanomaterials before the catalyzed splitting reactions of NH3 was carried out by XRD, N2 physisorption, N2O chemisorption, H2 TPD, CO2 TPD, NH3 TPD and H2 TPR. TEM and XPS were conducted on both fresh and used composites. Cu–Zn dispersion increased in the presence of TiO2. These spinel forms exhibited a strong Cu0.5Zn0.3Ti0.2O2–x (x = 0–1) structure interaction. Cu–Zn/CeO2 showed a 79% conversion of ammonia at 600 °C, whereas Cu–Zn/TiO2 demonstrated 63% at comparative operating conditions. A high catalytic activity, reflected in almost total consumption of ammonia at 700 °C with the hydrogen reactive production of 33.2 mmol g−1 min−1, was achieved over Cu–Zn/TiO2. No reactivity loss considering the NH3 depletion under applied reactor runs was detected, implying that materials had excellent time-on-stream stability. By scanning and transmission electron microscopy, bimetallic Cu–Zn was also observed, displaying a uniform TiO2 particle distribution on a structured sample surface. Impregnated zinc and copper species were uniformly distributed over Cu–Zn/TiO2. In the case of higher precursor content, a slight Cu domain agglomeration was noted. A heterogeneous mixed phase of Cu and Cu2O was present in all examined powders, as exposed by Cu L-edge spectra ratios.

Strong response of Pt clusters to the environment and conditions, formation of metastable states, and simple methods to trace the reversible changes.

Subnanometric metal particles, the so-called "clusters", are known to be responsive to their surroundings, but the detection of occurring changes, understanding the causes, and predicting the consequences are still extremely difficult for such small particles. Our study was aimed at estimating the potential of adsorption-based methods for these purposes. Using carbon monoxide as a probing molecule, which readily adsorbs on both bare and H-covered Pt surface, we have probed the adsorption properties of highly dispersed Pt/γ-Al2O3 samples after treatments under different atmospheres and temperatures (H2 or inert gas, 25-500 °C). The combined results of CO-chemisorption measurements, CO TPD, CO TPO, H2-by-CO displacement, and H2 TPD suggest that the system shuttles between two states: one with oxygen vacancies in the support and the other one with redox-active oxygen near the Pt clusters. These extreme states can be reversibly created and deleted, giving rise to innumerable intermediate structures that differ in the amount, binding strength, and/or reactivity of adsorbed species. Two adsorbates could act cooperatively, resulting in hydrogen spillover onto the support and making the adsorbate-metal-support interactions even more complex. Implications for better understanding the dynamic behavior of oxide-supported clusters and nanoparticles are discussed.

Ammonium salts modified silica supported Rh–Mn–Li catalyst for CO hydrogenation to C2 oxygenates

The silica (S0) was pretreated with slightly acidic (S1) or basic (S2) aqueous solutions of ammonium salts before using as a support to prepare Rh–Mn–Li catalyst for CO hydrogenation to C2 oxygenates. The results showed that the weak acidity of the modified silica stem from silanol groups where the number of free silanol groups increased as S0 < S1 < S2. This evolution could tune the interactions among support, Rh, and Mn components, and results in the variation of dispersion and chemical states of Rh species. Therefore, Rh/S1 catalyst with smaller Rh particle sizes and more Rh0 sites for CO dissociation exhibited higher CO hydrogenation activity, giving higher space time yield of C2 oxygenates of 766.1 g/kg/h than the untreated Rh/S0 catalyst (674.3 g/kg/h). Meanwhile, Rh/S1 catalyst has improved ethanol selectivity (19.3%) comparing with Rh/S0 (15.7%). Though Rh/S2 catalyst showed similar catalytic performance to Rh/S0 catalyst, it further increases the ethanol selectivity to 19.9%. The H2–TPD results suggested that the catalyst with high fraction of free silanol groups improved the migration of activated hydrogen spillover from metal Rh centers, where C2 oxygenates precursors adsorbed on the support could be hydrogenated into ethanol.

Surface structure-based CO2 reduction reaction modelling over supported copper catalysts

Reverse water gas shift (RWGS) is a promising green approach for CO2 capture and utilisation, which is able to valorise CO2 by reducing it to CO using hydrogen obtained via renewable electricity. Five different copper-based catalysts were synthesized – 10 wt. % Cu/M (M = Al2O3/CeO2/TiO2/SiO2/ZrO2). The catalysts were tested for activity under different conditions (pressure of 3–7 bars, temperature of 280–360 °C, 0.67–1.5 H2/CO2 reagent ratio and the gas flow rates in the range of 0.005–0.04 g/min). Cu/Al2O3 and Cu/CeO2 were the most active and reached near-equilibrium conversions at 360 °C. SEM, EDX, BET, XRD, XPS, HgP, H2 TPR, H2 TPD and N2O PSO techniques were used to characterise the catalysts. The present study is the first to demonstrate an unprecedented degree of linking the activity measurements, material surface-structure and mathematical modelling of mass transport phenomena coupled with copper microkinetics for the case of CO2 reduction.

The Effect of the Preparation Method of Bifunctional Fischer – Tropsch Catalysts on the Composition and Properties of Synthetic Fuel

The effect of the preparation method of bifunctional cobalt catalysts with HZSM-5 zeolite and a boehmite binder on the catalytic performance in the Fischer–Tropsch synthesis was studied. The synthesized catalysts were characterized by means of BET, XRD, EDX, SEM, TEM, H2 TPD and NH3 TPD methods and tested in the synthesis of hydrocarbons at a pressure of 2.0 MPa, temperature 240 °C, and gas hourly space velocity 1000 h–1. It was shown that the method of catalyst preparation can be used for controlling the hydrocarbon and fractional composition ofproducts of the Fischer – Tropsch synthesis. A promising composite catalytic system for the single-step synthesis of low-freezing diesel fuel was proposed.

Cerium-modified Ni-La2O3/ZrO2 for CO2 methanation

Abstract The key point in CO2 methanation is to improve the activity at low temperature and the stability. For this purpose, a new cerium-modified Ni-La2O3/ZrO2 catalyst was prepared using La1-xCexNiO3/ZrO2 with perovskite phase as the precursor, which was obtained by citrate complexation combined with an impregnation method. The resulting catalyst was characterized through Nitrogen adsorption and desorption, X-ray diffraction (XRD), Transmission electron microscopy (TEM), Hydrogen temperature programmed reduction (H2-TPR), Temperature-programmed desorption of CO2 (CO2-TPD) and that of H2 (H2-TPD), and X-ray photoelectron spectroscopy (XPS) techniques, and the catalytic performances for CO2 methanation was investigated. Cerium modification could improve the effective activation of CO2, thus enhancing the activity at low temperature for CO2 methanation. The metal Ni nanoparticles prepared using this method were highly dispersed and showed excellent resistance to sintering, leading to very good stability, which could be attributed to the following: Ni nanoparticles could be confined by cerium-modified La2O3; La2O3 could be confined by the cerium ions at the La2O3/ZrO2 interface; and the cerium ions were confined by ZrO2.

Selective aqueous-phase hydrogenation of D-fructose into D-mannitol using a highly efficient and reusable Cu-Ni/SiO2 catalyst

D-fructose hydrogenation in aqueous phase, at 373 K and 40 bar, was performed using monometallic and bimetallic Cu-Ni/SiO2 catalysts prepared by precipitation-deposition at controlled pH, without any type of co-catalysts and/or additives in solution. The precursors and catalysts were characterized by X-ray diffraction (XRD), N2 physisorption at 77 K, temperature programmed reduction (TPR), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS) analysis, temperature programmed desorption of H2 (H2-TPD) and X-ray photoelectron spectroscopy (XPS). The characterization of the mono and bimetallic samples showed that metal phase is composed of nanoparticles highly dispersed on SiO2 surface. It was also found evidence that a Cu-Ni like-alloy forms in the bimetallic sample. Precisely, the best catalytic performance was obtained with the bimetallic catalyst. This was attributed to a synergistic effect between Cu and Ni, favored by the intimate contact between both elements, which was reached from the Cu-Ni coprecipitation at controlled pH over SiO2. In a three cycles experiment performed with CuNi/SiO2, partial catalyst deactivation was observed. The original activity could be recovered by ex-situ reduction under H2 flow. By temperature programmed oxidation (TPO), it was found that this deactivation is due to surface carbon species strongly chemisorbed on the metallic phase.

On the deactivation of Ni-Al catalysts in CO2 methanation

This work provides detailed knowledge of long-term deactivation of Ni catalysts in CO2 methanation. NiAlOx mixed oxides with varying Ni loading as well as a 17 wt-% Ni/γ-Al2O3 catalyst were synthesized via co-precipitation and incipient wetness impregnation, respectively. The catalysts were aged at 523, 573 and 623 K under equilibrium conditions up to 165 h. Periodic activity measurements under differential conditions reveal severe deactivation. The stability of co-precipitated systems increases with decreasing Ni content on the expense of catalyst activity. Ni/γ-Al2O3 exhibits a lower stability as a comparable mixed oxide. A power law model is applied for the kinetic description of deactivation. Catalyst samples are characterized by means of temperature programmed desorption of H2 (H2-TPD) and CO2 (CO2-TPD), pulsed H2 chemisorption, XRD, FT-IR spectroscopy, XPS and N2 physisorption. Main deactivation mechanisms in the co-precipitated samples are found to be Ni particle sintering, a loss of BET surface area as well as a reduction of CO2 adsorption capacity and medium basic sites, along with structural changes of the mixed oxide phase. Ni particle growth and a decrease in BET surface area lead to deactivation of the impregnated sample. Structure-activity correlations imply a complex interplay of governing deactivation phenomena as well as structure sensitivity.

Correlation between synthesis pH, structure and Cu/MgO/Al2O3 heterogeneous catalyst activity and selectivity in CO2 hydrogenation to methanol

Cu/MgO/Al2O3 catalysts were synthesized by a co-precipitation preparation method, varying pH, while their catalytic performance was evaluated in a continuous-flow packed-bed reactor to relate the catalytic material activity, selectivity and stability with its surface structure. The major reaction products were methanol and water with CO as a sole process by-product. Alkaline synthesis conditions (pH = 8) positively affected CO2 conversion and CH3OH yield (< 250 °C), as CuO and Cu2O phases were present, since Cu2+ was only partially reduced. The hydrogen consumption variation also indicated that these different Cu species changed the interaction with magnesium and alumina. An increase in active basic sites was ascribed to the formation of spinel CuAl2O4 and MgAl2O4. Alongside with H2 TPD, XRD and SEM data suggested that a higher precursor solution pH enhanced the dispersion of CuO, enlarged Cu and BET areas, and improved the adsorption of H2. The XPS profiles of fresh, pre-treated and spent heterogeneous catalysts indicated that the dispersed copper moieties were reduced (to Cu0 or Cu+) during CO2 hydrogenation. CO2 turnover was consistent with metallic atom distribution, derived from N2O measurements. A maximum TOF of 13.2 × 10–4 s–1 was obtained over the catalyst, prepared at the pH of 8, whereas a minimum TOF of 5.5 × 10–4 s–1 corresponded to the pH of 5. A volcano plot-type shape of the productivity and basicity versus pH was observed as well, as the highest methanol productivity was attained using the precipitation pH of 8 (200 °C operation).

Effect of alkaline earth metal oxide (MO) Cu/MO/Al2O3 catalysts on methanol synthesis activity and selectivity via CO2 reduction

Heterogeneous copper/alumina catalysts with MgO, CaO, SrO, and BaO were prepared by co-precipitation synthesis method and characterized by means of N2-sorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and subsequent H2 temperature-programmed reduction (H2 TPR) and H2/CO2 temperature-programmed desorption (H2 and CO2 TPD). The incorporation of oxides increases the metallic Cu surface area, as follows: Mg > Sr > Zn > Ca > Ba. These metal oxides thus increased the interaction between CuO and Al, resulting weaker reducibility of CuO. MgO increased the number of carbon dioxide and hydrogen adsorption active sites, whereas Ba augmented the basicity of the material. The activity with respect to methanol production matched the increase of Cu surface. As CH3OH selectivity monotonically decreased with the temperature, CO increased proportionally. Among the examined catalytic materials, Cu/MgO/Al2O3 exhibited a higher reactant conversion than the pelletized commercial analogues. Hydrogenation performance of the catalysts thus depended on both, the Cu surface site availability and the interaction between copper–metal oxides. While the industrial Cu/ZnO/Al2O3 has been extensively employed for quite some time, it is demonstrated herein that even upon the application of inexpensive non-critical raw material resources, such as MgO, an increment in bifunctional catalysis performance is attained. The Cu/Mg/Al catalyst showed a turnover frequency of 11.9 × 10−4 s−1, which is higher than the commercial HFR120 and LURGI catalysts.

Synthesis of Low-Pour-Point Diesel Fuel in the Presence of a Composite Cobalt-Containing Catalyst

Production of synthetic diesel fuel by the Fischer–Tropsch (FT) method in the presence of a composite catalyst prepared by mechanically mixing 35 wt % Co/SiO2, 30 wt % HZSM-5, and 30 wt % Al2O3 has been studied. The catalyst has been characterized by the H2 TPR, H2 TPD, NH3 TPD, XRD, SEM, and TEM methods. Catalytic properties have been studied in a fixed-bed flow reactor at 2 MPa and a GHSV of 1000 h–1 in the temperature range of 230–250°C. The highest efficiency and C5+ HC selectivity values of 130 kg/(m3 h) and 72.5%, respectively, are achieved at 250°C. The low-temperature properties of the synthetic diesel fuel meet the requirements for winter diesel.

Characterization of nickel catalysts with transient methods

The Ni surface area is a key factor in catalytic performance of supported Ni catalysts employed in heterogeneously catalyzed reactions. For its characterization, transient measurement techniques are powerful but need a proper experimental design and a high level of accuracy. In this study, several transient methods, namely temperature programmed desorption of H2 (H2-TPD), pulsed H2 chemisorption and N2O chemisorption, were applied and evaluated for the characterization of Ni catalysts. Results were compared with those from static H2 chemisorption. Ni powder, as well as NiAlOx and Ni/γ-Al2O3 with varying Ni loadings, synthesized via precipitation and incipient wetness impregnation, respectively, were used as model catalysts. H2-TPD within the temperature range from 84 to 753K is able to completely describe the interaction of H2 with supported Ni. However, a quantitative analysis of the specific Ni surface area based on H2-TPD is difficult whereas pulsed H2 chemisorption leads to comparable results as obtained from static measurements. Adsorption and pre-treatment conditions have a strong impact on the desorption spectra. Reversible morphologic changes of the Ni surface were revealed by H2-TPD when changing the gas atmosphere during pre‐treatment. N2O chemisorption occurs in three steps including fast oxygen uptake, growth of the oxide layer and subsequent layer thickening due to subsurface and bulk oxidation. A separation of surface and subsurface/bulk oxidation of NiAlOx and Ni/γ-Al2O3, both of which are readily oxidized even under mild conditions, is only achievable at temperatures between 190 and 195K. In this temperature range, the ratio of adsorbed oxygen atoms, O, and the number of Ni surface atoms, NiS, (O/NiS) is 0.38±0.07, which can be applied for specific Ni surface area determination. The experimental mode of N2O chemisorption (flow or titration mode) does not influence the extent of subsurface oxidation. The separation of surface and subsurface/bulk oxidation is more feasible in the case of Ni powder. Here, a suitable temperature for Ni surface area determination lies within 265 and 285K with an O/NiS ratio of 0.96±0.05.

The Catalytic Hydrogenation of Biomass Platform Molecules by Ni–Co Nanoalloy Catalysts

Ni–Co nanoalloy catalysts have been prepared by a simple solid phase reaction approach and were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature-programmed desorption of H2 (H2-TPD) and X-ray photoelectron spectroscopy (XPS). The Ni–Co nanoalloy catalyst was evaluated for hydrogenation of d-glucose under aqueous phase condition. The results indicated that the Ni–Co nanoalloy catalysts were more active than the single metal Ni or Co nano-catalyst. Moreover, Ni–Co nanoalloy catalyst with the molar ratio of Co/Ni = 1 showed the highest catalytic activity in hydrogenation reaction. It was observed that metallic Ni in Ni–Co nanoalloy was more negatively charged, which was favorable for improving the catalytic activity. In addition, the present catalyst was found to be extended for the efficient hydrogenation of the various biomass platform molecules, which showed comparable activity and selectivity with that of Pd/C catalyst. The XRD, TEM and XPS characterization of the spent nanoalloy catalyst indicated that the slight aggregation, crystallization, and surface oxidation happened in the consecutive catalytic recycles, resulting in the deactivation of catalyst. Finally, the reaction kinetics of d-glucose hydrogenation has been also investigated.

Palladium Promoted Production of Higher Amines from a Lower Amine Feedstock

The catalytic (Pd/Al2O3 and Pd/C; mean Pd size 2.5–3.0 nm from (S)TEM analysis) synthesis of di-butylamine (DBA) and tri-butylamine (TBA) from mono-butylamine (MBA) and DBA, respectively, in continuous gas phase operation is demonstrated. Exclusive production of DBA (from MBA) has been established over both catalysts where 453 ≤ T ≤ 523 K (∆Ea = 79 kJ mol−1). Greater activity for Pd/C is associated with higher levels of surface acidity (from NH3 chemisorption/TPD) and spillover hydrogen (from H2 TPD). Reaction of DBA over both catalysts when configured in series delivered full selectivity to TBA. Our results establish a novel clean alternative route for the continuous production of higher (secondary and tertiary) amines.Graphical

Methanation of CO2 on Ni/γ-Al2O3: Influence of Pt, Pd or Rh promotion

Methanation of carbon dioxide was carried out in a plug flow reactor (CO2:H2=1:4, GHSV=5700h−1) over a series of noble metal promoted Ni/γ-Al2O3 catalysts, prepared by the co-impregnation method: Ni(10wt.%)-Pt(0.5wt.%)/γ-Al2O3, Ni(10wt.%)-Pd(0.5wt.%)/γ-Al2O3, and Ni(10wt.%)-Rh(0.5wt.%)/γ-Al2O3. Characterization of catalysts was performed by N2 adsorption–desorption isotherms at −196°C (BET), X-ray powder diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of H2 (H2-TPD), and CO2 (CO2-TPD). Promotion by noble metals resulted in better reducibility of NiO (Ni-Rh>Ni-Pt>Ni-Pd>Ni), enhanced metal dispersion and H2 chemisorption capacity (Ni-Pt>Ni-Rh>Ni-Pd>Ni), with no significant influence upon the support intrinsic activity given by the CO2 adsorption capacity. Catalytic activity of the promoted catalysts compared to the unpromoted one was performed by temperature programmed reactions (TPRea, 30–300°C) and stability tests at 250°C, under atmospheric pressure, and was evaluated in relation with the structural and functional properties of the catalysts. Promotion by Pt and Pd of Ni/γ-Al2O3 resulted in enhanced CO2 conversion and CH4 selectivity values in the 180–270°C domain, while Ni-Rh/γ-Al2O3 was inferior to Ni/γ-Al2O3. Considering the stability, all catalysts show stable catalytic performance over the investigated time range, with CH4 selectivity values above 90%. Ni-Pd/γ-Al2O3 is the most efficient catalyst, with stable CO2 conversion of 74.6% and CH4 selectivity of 96.6% at 250°C, in addition to the maximum values of 90.5% and 98.7%, respectively, at 300°C, obtained during temperature programmed reaction runs.

Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold

A range of oxides (γ-Al2O3, TiO2, ZrO2, CeO2, α-Fe2O3 and Fe3O4) with different redox properties were used to support nano-scale (mean=2–8nm) Au and employed in the gas phase hydrogenation of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H2/O2 titration, H2 TPD, XRD, TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible supports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies (demonstrated by O2 titration) that inhibit Au particle sintering during catalyst activation. Electron transfer to generate charged Au species (determined by XPS) correlates with support ionisation potential. Higher nitrobenzene hydrogenation (to aniline) TOFs were recorded relative to benzaldehyde where rate increased with decreasing Au size (from 8 to 4nm) with measurably lower TOF over Au <3nm. Strong binding of CHO and NO2 functions to oxygen vacancies resulted in lower hydrogenation rates. Higher temperatures (>413K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation of Auδ− on non-reducible Al2O3 favoured selective reduction of CHO with full selectivity to benzyl alcohol at 413K.

Studies on Ni–M (M = Cu, Ag, Au) bimetallic catalysts for selective hydrogenation of cinnamaldehyde

Bimetallic catalysts of the type Ni–M with M=Cu, Ag and Au, and supported on TiO2-P-25 have been prepared by chemical reduction using glucose as the reducing agent. Hydrogenation of cinnamaldehyde (CAL) to yield hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been studied on the catalysts in the temperature range 60–140°C and at 20kg/cm2 pressure, with methanol as solvent. Ni crystallite sizes, measured by X-ray line broadening analysis (XLBA), H2 pulse chemisorption and Transmission Electron Microscope (TEM) techniques, are in the range 8–12nm. Temperature Programmed Reduction (TPR) and Diffuse Reflectance Spectroscopic (DRS) studies indicate the formation of Ni–Cu alloys, while Ni–Ag and Ni–Au exist as bimetallic nanoparticles. High-resolution HRTEM studies show that the bimetallic nanoparticles are in close contact, forming hetero junctions. Changes in the XPS binding energy values for Ni 2p1/2 and Ni 2p3/2 levels reveal that Cu/Ag/Au, tend to increase electron density around Ni, which retards the adsorption of CAL via olefinic bond and weakens NiH bond strength. H2 TPD measurements also indicated weakening of NiH bond. Bimetallic catalysts display higher CAL conversion and selectivity to COL vis-à-vis the corresponding monometallic catalysts at lower reaction temperatures, 60–80°C. But, selectivity to COL decreases at higher temperatures, 100–120°C. Mode of adsorption of CAL and nature of adsorbed hydrogen on bimetallic catalysts influence their activity and selectivity.

Synthesis of carbon-supported Pd/SnO2 catalyst for highly selective hydrogenation of 2,4-difluoronitrobenzene

Halogenated anilines have a wide range of applications in the production of pharmaceuticals and agrochemical substances, and thus it is of great importance to develop highly active and selective catalysts for the hydrogenation of halogenated nitrobenzenes. We approach this challenge by probing noble metal/non-noble metal oxide nanoparticles (NPs) catalysts. Carbon-supported Pd/SnO2 catalysts were synthesized by the chemical reduction method, and their catalytic activity was evaluated by the hydrogenation reaction of 2,4-difluoronitrobenzene (DFNB) to the corresponding 2,4-difluoroaniline (DFAN), showing a remarkable synergistic effect of the Pd and SnO2 NPs. The as-prepared Pd/SnO2/C catalysts were characterized using TEM, XRD, H2 TPD and XPS techniques. Modifications to the electronic structure of the Pd atoms through the use of SnO2 led to the suppression of the hydrogenolysis of the CF bond and the acceleration of nitrosobenzene (DFNSB) conversion and consequently, resulted in the inhibition of the formation of reactive by-products and may be responsible for the enhancements observed in selectivity.