N2O Pulse Chemisorption Research Articles

Integrating the Hydrogenation of Nitrobenzene over Cu/Mgo Catalysts with the 1, 4-Butanediol Dehydrogenation Reaction

Using a fixed bed reactor and Cu/MgO catalysts, the hydrogenation of nitrobenzene to aniline has been combined with the dehydrogenation of 1,4-butanediol to c-butyrolactone reaction in the vapour phase. These Cu/MgO catalysts were made using the co-precipitation method, and they were examined using techniques for BET surface area, XRD, TPR, and N2O pulse-chemisorption. It has been described how the hydrogenation of nitrobenzene over Cu/MgO catalysts coupled with the 1,4-butanediol dehydrogenation reaction has a positive effect.

Dry (CO2) reforming of methane over zirconium promoted Ni-MgO mixed oxide catalyst: Effect of Zr addition

Dry (CO2) reforming of methane (DRM) for syngas production has gained great attraction since it utilizes two major green house gases (CH4, CO2). However, this process is still far from commercialization due to the catalyst deactivation by coking and metal sintering. In this present work, we have prepared a series of Zr promoted Ni/MgO catalysts using Incipient wetness impregnatiom (IWI) method and applied for (DRM) reaction at temperature range of 500–800 °C. The prepared fresh and spent catalysts were fully characterized with various adsorption and spectroscopic techniques such as XRD, BET-SA, ICP-OES, H2-TPR, CO2-TPD, N2O-pulse chemisorption, SEM, TEM, TGA and O2-TPO. Reduced samples TEM analysis revealed that Zr modified catalysts possessed smaller Ni particles size and N2O-pulse chemisorption results showed that Ni dispersion is improved with Zr addition compared to Ni/MgO. In addition, CO2-TPD analysis confirmed that the basicity gradually increases with the addition of Zr and it enhances the CO2 adsorption capacity. DRM experimental results demonstrated that among all the tested catalysts Ni/3Zr/MgO exhibited remarkable activity and stable conversion with CH4 (78 %), CO2 (91 %) and H2/CO ratio (0.92) over a period of 70 h time on stream without deactivation. Further, CH4-temperature programmed surface reaction (TPSR) proved that Zr promoter significantly decreases the CH4 dissociation energy which could be due to smaller Ni particles, strong metal-support interaction and high Ni metal dispersion.

Simultaneous synthesis of aniline and γ-butyrolactone from nitrobenzene and 1,4-butanediol over Cu-CoOx-MgO catalyst via catalytic hydrogen transfer process: Effect of calcination temperature

This study examined a hydrogen transfer reaction from 1,4-butanediol to nitrobenzene for γ-butyrolactone and aniline simultaneously over Cu-CoOx-MgO catalysts. The catalyst was developed by co-precipitation followed by metal hydroxycarbonate mixing and calcination at three different temperatures (500, 700, and 900 °C). The hydrogenation of nitrobenzene to aniline and the dehydrogenation of 1,4-butanediol to γ-butyrolactone was accomplished in a gas-phase fixed-bed continuous reactor system at 250 °C. The catalyst Cu-CoOx-MgO-500 calcined at 500 °C showed outstanding performance because of the higher copper dispersion and negligible spinel species (CuCo2O4 /MgCo2O4) compared to the other two catalysts. The order of activity decreased with increasing calcination temperature from 500° to 900°C. The activity trend followed the order, Cu-CoOx-MgO-500 > Cu-CoOx-MgO-700 > Cu-CoOx-MgO-900. The effect of calcination on the catalytic properties was analyzed by atomic absorption spectroscopy elemental analysis, Brunauer-Emmett-Teller surface area, N2O pulse chemisorption, temperature-programmed reduction-H2, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that Cu-CoO-MgO-500 exhibited more active copper sites (Cu0/Cu+1) and optimal metal-support interactions that decrease the reduction temperature of copper. On the other hand, Cu-Co and Mg-Co spinel (CuCo2O4/MgCo2O4) content, which adversely affects the catalyst activity, increased with increasing calcination temperature. In summary, simultaneous hydrogenation and dehydrogenation reactions via hydrogen transfer reactions have potential commercial applications.

Hydrogenation of CO2 to methanol using Cu-based catalyst supported on oxide pellets

Hydrogenation of CO2 into methanol is one of the most economical process to reduce CO2 concentration in the atmosphere. Since methanol is an industrial commodity used in chemical products as well as transportation fuel, this process has gained considerable interest, which enables the effective utilization of CO2. Nevertheless, the efficiency of direct CO2 hydrogenation to produce methanol is strongly reliant on the activity of the catalyst. In this regard, the present work highlights the synthesis of methanol, catalytic evaluation and characterization of catalysts Cu/ZnO supported on Al2O3 and SBA-15 pellets with the addition of group IV, V and VII metal oxides mixture as promoters. The catalysts were systematically prepared via impregnation technique with fixed Cu:Zn and promoter ratio from group VII:V:IV. The synthesized catalysts were characterized by H2-temperature-programmed reduction (H2-TPR), field emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), N2 adsorption-desorption and N2O pulse chemisorption method. The crushing strength of the pellets were also tested. Catalytic performances were evaluated for methanol synthesis from CO2 hydrogenation in a tubular, stainless steel fixed-bed reactor at 250 °C, 2 MPa, gas hourly space velocity (GHSV) 4000 ml/g.h and H2/CO2 ratio of 3:1. The tri-promoted Cu/ZnO supported on Al2O3 pellet resulted in CO2 conversion of 13.3 % compared to 11.61 % from that of SBA-15-supported catalyst. However, the catalyst supported on SBA-15 pellet exhibited 54.59% methanol selectivity, whereas Al2O3-supported catalyst only resulted in 46.73 % methanol selectivity.

Cu-ZnO@Al2O3 hybrid nanoparticle with enhanced activity for catalytic CO2 conversion to methanol

A facile approach is demonstrated for the fabrication of Cu-ZnO-based hybrid nanostructures for the catalytic CO2 conversion to methanol. The method combines colloid stabilization of Al2O3 nanoparticles (as support material) and controlled co-precipitation of Cu (active metal) and ZnO (promoter) onto the Al2O3 nanoparticles. Complementary approaches, including X-ray diffractometry, Brunauer-Emmett-Teller surface area analysis, N2O pulse chemisorption, CO2-based temperature-programmed desorption, transmission electron microscopy coupled with energy dispersive spectroscopy, inductively coupled plasma optical emission spectrometry and thermal gravimetric analysis are employed for the characterization of catalyst materials. The results show a successful synthesis of ultrafine Cu-ZnO nanocrystallites deposited on the Al2O3 nanoparticle clusters (Cu-ZnO@Al2O3). Hybridization with Al2O3 nanoparticles enhanced metal dispersion and number of basic sites of the Cu-ZnO-based nanocatalyst. Aminosilane-based surface functionalization on the Al2O3 nanoparticle increased metal surface area in the hybrid nanostructure. The CO2 conversion catalyzed by the synthesized Cu-ZnO@Al2O3 was shown to be proportional to active surface area of the hybrid nanostructure. An optimum selectivity of the synthesized catalyst was identified (≈47–49%) when the mass fraction of Al2O3 was (35–36) %, in correspondence to the highest moderate basicity of the synthesized hybrid nanostructures. The highest yield of methanol achieved 12989 ± 2007 µmolg−1 h−1 by the developed Cu-ZnO@Al2O3. Our work demonstrates a prototype study of fabricating high-performance hybrid nanocatalyst with the support of mechanistic understanding in material synthesis for the synergistic catalysis of CO2 hydrogenation to methanol.

Mesoporous silica–supported copper catalysts for dehydrogenation of biomass-derived 1,4-butanediol to gamma butyrolactone in a continuous process at atmospheric pressure

A series of Cu/SBA-15 catalysts were prepared by wet impregnation method and tested for dehydrogenation of 1,4-butanediol (1,4-BDO) to γ-butyrolactone (GBL). As-synthesized catalysts were characterized by different techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), N2 physisorption, N2O pulse chemisorption, and transmission electron microscopy (TEM) analysis. Among the series of Cu/SBA-15 catalysts, 10 wt% Cu/SBA-15 catalyst exhibited a complete conversion of 1,4-BDO with 98% selectivity to GBL. The superior catalytic performance of the 10 wt% Cu/SBA-15 catalyst was attributed to the well dispersion of Cu particles with much number of active metallic Cu sites over high surface area, SBA-15 support, and surface acidity.

Low-temperature hydrogenation of dimethyl oxalate to ethylene glycol via ternary synergistic catalysis of Cu and acid−base sites

Metal-support synergistic catalysis plays a crucial role in heterogeneous reaction processes from viewpoint of both fundamental research and practical applications. Herein, a series of Cu-based nanocatalysts were prepared by virtue of topotactic structure transformation from CuMgAl-layered double hydroxide (CuMgAl − LDH) precursors. Various in situ investigations including XRD, XPS, EXAFS and FTIR demonstrate that the structural transformation of CuMgAl − LDH results in well-dispersed Cu nanoparticles (metallic Cu° as the single species) supported on mixed metal oxides (MgO and Al2O3, denoted as Cu/MMO). The optimal catalyst (Cu/MMO−S3) exhibits an excellent catalytic performance toward hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) (yield: 94.4%) at an exceptionally low operation temperature (438 K). This is, to the best of our knowledge, at least 30―40 K lower than normally accepted temperature for Cu-based catalysts (above 473 K). Structure − property correlation investigations were performed via in situ FTIR, N2O pulse chemisorption, NH3−TPD and CO2−TPD, and the results revealed that a ternary synergistic catalysis of Cu and acid − base sites makes a predominant contribution: Lewis acid sites (Al3+) and medium-strong basic sites (Mg2+−O2− pair) of supports serve as active sites for adsorption of polarized CO/CO group in DMO molecule; while H2 undergoes dissociation adsorption on Cu° site. This precise control over metal and acid − base sites based on LDHs precursor approach would lead to new possibilities in rational design and preparation of heterogeneous catalysts for hydrogenation of CO/CO group.

Magnesium Aluminate Supported Cu Catalyst for Selective Transfer Hydrogenation of Biomass Derived Furfural to Furfuryl Alcohol with Formic Acid as Hydrogen Donor

AbstractCatalytic transfer hydrogenation (CTH) was concerned great attention because it does not need the use of high pressure H2. A series of Cu catalysts has been prepared for transfer hydrogenation of biomass derived furfural to furfuryl alcohol with formic acid. The prepared Cu based catalysts are thoroughly characterized by various technique such as XRD, TPR, TPD (NH3, CO2), TEM, FT‐IR, UV‐Vis, N2O pulse chemisorption and N2‐physorption method. For a comparison point of view, the activity tests of various copper based catalysts have also been carried out. Among all these, MgAl2O4 (MA) supported copper catalyst was found to be the best to give 90% selectivity of furfuryl alcohol from transfer hydrogenation of furfural. The excellent yield of furfuryl alcohol could be attributed to high density of surface active Cu species, proper surface acidic‐basic properties and metal support interaction. Moreover, Cu/MA catalyst was simply recovered and reused, which retained its original activity even after reaction without significant loss of original activity. Supporting its reusability and stability.

Role of the Feed Gas on the Selective Catalytic Dehydrogenation of Benzyl Alcohol over Cu/Hydrotalcite Catalyst

AbstractThe present work highlights the utilization of CO2 as feed gas for the catalytic dehydrogenation of benzyl alcohol to benzaldehyde over supported Cu catalysts in continuous process. Powder X‐Ray Diffraction (XRD) patterns, N2O pulse chemisorption results, H2‐Temperature Programmed Reduction (H2‐TPR) profiles and Transmission Electron Microscopy (TEM) analysis suggests that Cu/hydrotalcite possess high dispersion with small Cu atoms. Due to the united effects of high metal dispersion and bifunctional acid base properties (as evidenced by Temperature Programmed Desorption (TPD) of CO2 and NH3), Cu/hydrotalcite catalyst offers better activity than Cu/Al2O3 and Cu/MgO. The presence of CO2 promotes reverse water gas shift reaction by consuming the in‐situ generated H2 in dehydrogenation process and maintains stable benzaldehyde selectivity. Whereas the presence of N2 promotes the disproportionation reaction and leads to decrease in benzaldehyde selectivity.

Selective vapour phase dehydrogenation of biomass-derived 1,4-butanediol to gamma butyrolactone over Cu/ZrO2 catalysts: influence of La2O3 promotor

A series of Cu/ZrO2–La2O3 catalysts with various La2O3 loadings were prepared by coprecipitation method and tested for the synthesis of γ-butyrolactone by dehydrogenation of 1,4-butanediol. The catalysts were characterized by XRD, TPR, FT-IR, TPD of NH3 and CO2, SEM, HRTEM and N2O pulse chemisorption studies. The results revealed that the specific surface area, dispersity of Cu species and metallic Cu surface area were increased by the addition of La2O3 but also prevented the agglomeration of metal particles and acidity of the catalysts. The 5 wt.% La2O3/Cu/ZrO2 exhibited excellent yield (96%) of γ-butyrolactone compared to Cu/ZrO2 and 3 wt.% La2O3/Cu/ZrO2 catalysts and it has shown consistent activity and selectivity during 15 h on stream study. Dehydrogenation of biomass-derived 1,4-butanediol to γ-butyrolactone with high yield over La2O3-modified Cu/ZrO2 catalysts at atmospheric pressure in a continuous process was achieved.

Synthesis of Hydrocinnamaldehyde via Vapor Phase Dehydrogenation of Hydrocinnamyl alcohol over Rice‐Derived MgO‐Supported Copper Catalysts

AbstractGreen synthetic method for the production of hydrocinnamaldehyde via vapour phase dehydrogenation of hydrocinnnamyl alcohol over high surface area MgO (HSA‐MgO) supported Cu catalyst at atmospheric pressure without using any additives has been attempted. Cu/HSA‐MgO catalysts have been prepared by thermal decomposition of cooked rice grains mixed with magnesium acetate followed by wet impregnation by Cu. The prepared catalysts have been characterized by various physiochemical characterization techniques such as TGA, XRD, BET surface area, TPD of CO2, H2‐TPR, TEM, SEM, EDX and N2O pulse chemisorption. Among all the catalysts, 10%Cu/HSA‐MgO catalyst is found to be the best catalyst with 78% conversion of hydrocinnnamyl alcohol and 96% selectivity of hydrocinnamaldehyde. N2O pulse chemisorption and TPR analysis results divulge the high dispersion of smaller copper particles on the surface of HSA‐MgO support which is considered to be responsible for its superior catalytic activity.

Coupling of ortho-chloronitrobenzene hydrogenation with 1,4-butanediol dehydrogenation over Cu[sbnd]MgO catalysts: A hydrogen free process

Aiming at an efficient method for the hydrogenation of o-chloronitrobenzene to o-chloroaniline under hydrogen free environment, the reaction was coupled with 1,4-butanediol dehydrogenation over CuMgO catalysts containing various amounts of copper loadings (5–20wt%). o-Chloroaniline and γ-butyrolactone were the main products with the yield of 85% and 90%, respectively. The main advantage of the coupling process was that the hydrogenation reaction was conducted at the lower temperature (523K) without external hydrogen supply when compared to the independent hydrogenation (648K). Catalysts were characterized using various analytical techniques such as BET, XRD, N2O pulse chemisorption, TPR-H2, XPS and CHNS analysis. From N2O characterization results, it was found that 10wt% CuMgO catalyst containing more surface Cu species (Cu0/Cu+1) showed a superior performance in the coupling process.

Direct activation of CH4 to oxygenates and unsaturated hydrocarbons using N2O on Fe-modified zeolites

Direct activation of CH4 to oxygenates and unsaturated light hydrocarbons was investigated using Fe-modified ZSM-5 and Ferrierite (FER) for a partial oxidation of CH4 with N2O oxidant. The amount of active α-oxygen sites and number of Bronsted acid sites on the Fe-modified zeolites were well correlated with CH4 conversion rate and product distributions. The amount of α-oxygen sites was largely changed according to preparation method such as wet impregnation or ion-exchange of iron precursor and types of zeolites. A large number of Bronsted acid sites and α-oxygen sites on the Fe-modified FER revealed a higher oxygenate formation such as methanol and dimethyl ether (DME) with COx, and a larger number of strong acid sites on Fe-modified ZSM-5 was also responsible for a higher selectivity to light hydrocarbons by a successive dehydration of oxygenates formed. The different catalytic performances were verified through proper measurements of the amount and type of acidic sites as well as the α-oxygen sites measured by N2O pulse chemisorption. The Fe-modified FER prepared by impregnation method possessed a larger amount of α-oxygen sites due to abundant Bronsted acid sites, which was responsible for a higher rate of CH4 conversion to oxygenates with the help of N2O decomposition on the α-oxygen sites originated from iron oxide nanoparticles.

Passivation and reactivation of catalyst systems for the single step synthesis of dimethyl ether from CO-rich synthesis gas

A methanol catalyst based on Cu/ZnO/Al2O3 (CZA) was prepared and mixed with four different solid acids, a pure γ-Al2O3, a SiO2-doped γ-Al2O3, an AlPO4-doped γ-Al2O3 and the zeolite H-MFI 400, respectively. These admixed catalyst systems were tested in the direct synthesis of dimethyl ether from CO-rich synthesis gas (CO:H2=1), which is typical for biomass-derived synthesis gas. Reactions were carried out in a laboratory plant at 250°C and 51bar for 120h time-on-stream followed by catalyst passivation with O2 and regeneration by hydrogenation. After catalyst regeneration, the reaction was run again for another 72h. The catalyst system containing the zeolite exhibited highest CO-conversion. However, all catalysts showed a drop of activity after the passivation- and regeneration-process and the system with the SiO2-doped γ-Al2O3 showed the lowest loss of activity. Investigation of the catalysts after reaction by N2O-pulse chemisorption and XRD revealed that agglomeration of catalyst species took place leading to an increased Cu0-particle size for all systems. This phenomenon was less pronounced in the case of the system containing the SiO2-doped γ-Al2O3. Thus, the main cause of catalyst deactivation was found to be sintering of the catalytically active components.

Zeolite-based bifunctional catalysts for the single step synthesis of dimethyl ether from CO-rich synthesis gas

Zeolite-based bifunctional catalysts for the production of dimethyl ether (DME) from CO-rich synthesis gas (H2:CO=1) were prepared via various preparation methods including co-precipitation–impregnation, impregnation, co-precipitation sedimentation and oxalate co-precipitation. The catalysts comprise a Cu/ZnO/Al2O3 component for methanol formation and zeolite H-MFI 400 as acidic component for methanol dehydration to DME. An admixed catalyst system was used as reference and all catalysts were characterized by SEM-EDX, XRF, N2-physisorption, XRD, H2-TPR, NH3-TPD, N2O-pulse chemisorption and TEM. The catalysts were tested in a continuously operating laboratory plant and the experiments revealed that the synthesis strategy strongly influences catalyst properties and hence catalyst activity. Especially a bifunctional catalyst prepared via oxalate co-precipitation proved to be highly active and could compete with conventional admixed catalyst systems. High CO-conversion and a high DME-selectivity could be reached. Catalyst characterization revealed that high Cu surface areas, small Cu particle sizes and a high number of moderate acidic sites are crucial to achieve maximum catalytic performance.

Impact of K and Ba promoters on CO2hydrogenation over Cu/Al2O3catalysts at high pressure

CO2 hydrogenation over K and Ba promoted Cu/Al2O3 catalyst was systematically investigated to study the promoter effects in a wide range of pressure conditions. The catalysts prepared by the impregnation method were characterized by XRD, physisorption, N2O-pulse chemisorption, H2-TPR, and CO2-TPD techniques. The catalytic performance was evaluated using a fixed-bed microreactor for a pressure and temperature range of 0.40–36 MPa and 443–553 K. The influence of promoters on the formation of surface species present during the reaction was examined by in situ DRIFTS. As expected from thermodynamics, high pressure and low temperature are the favourable conditions to achieve high selectivity to methanol over the Cu/Al2O3 catalyst. Improved reaction performance towards methanol synthesis and reverse water-gas shift (RWGS) reaction was observed for the Ba and K promoted Cu/Al2O3 catalysts, respectively. Notably, with the Ba promotion the selectivity to methanol was enhanced to 62.2% compared to 46.6% of the unpromoted Cu/Al2O3 catalyst at 10 MPa and 473 K at the expense of a lowered CO2 conversion. In contrast, the K promoted catalyst exhibited high selectivity to CO (95.8%) under the same reaction conditions. Formation of dimethyl ether, significant over the unpromoted Cu/Al2O3 catalyst at 0.4–10 MPa, was strongly suppressed at 36 MPa. Ba and K promoters effectively suppressed the formation of dimethyl ether under all examined pressure conditions by weakening the acidity of the alumina support. The strong promotional effects of K was explained by the predominant coverage of both Cu and alumina surface sites, creating specific active sites stabilizing surface intermediate species and preferring the RWGS pathway. On the contrary, the Ba promoter covers the alumina surface exclusively and renders Cu accessible and more easily reducible, promoting methanol synthesis. The effects of promoters on the catalytic performance were found to be valid at low and at elevated pressures.

Coupling of Cyclohexanol Dehydrogenation-nitrobenzene Hydrogenation Over MgO-Al2O3 Hydrotalcite Supported Cu Catalysts: Effect of Cu Loading

A series of Cu/ (MgO-Al2O3) hydrotalcite catalysts have been prepared by impregnation technique with a Cu loading ranging between 5 to 25wt%. The prepared catalysts have been characterized by BET technique, X-Ray diffraction, temperature programmed reduction (TPR) and N2O pulse chemisorption techniques. Cyclohexanol dehydrogenation and nitrobenzene hydrogenation (individual reactions) and coupling of these two reactions have been performed over these catalysts in vapor phase at atmospheric pressure and at 548K. XRD results reveal the intactness of hydrotalcite structure in reduced and used catalysts with Cu loadings below 15wt%. The beauty of the coupling reaction is to yield cyclohexanone and aniline from cyclohexanol and nitrobenzene respectively with stoichiometric quantity of H2 usage for nitrobenzene hydrogenation. The catalyst with 10wt% Cu loading showed higher activity in the coupling reaction which could be attributed to the better Cu dispersion, smaller Cu particle size and relatively more number of Cu active species presented on the surface of the catalyst.

Highly active Cu/MgO catalysts for selective dehydrogenation of benzyl alcohol into benzaldehyde using neither O2 nor H2 acceptor

Aiming at developing an efficient catalyst for selective dehydrogenation of benzyl alcohol into benzaldehyde in the absence of O2 and H2 acceptor, a series of Cu/MgO catalysts with Cu loading of 1, 3, 5, and 7% have been prepared, of which the 5% Cu/MgO catalyst in the gas phase exhibited a remarkable performance with 98% conversion and 97% selectivity and in support of the performance, the catalysts have been characterized by different techniques like BET surface area analysis, XRD, TEM, CO2-TPD, N2O pulse chemisorption, XPS and TPR.