H2-TPR Profiles Research Articles

Robust synergistic effect between Zn1Mo1 bifunctional TiO2 for efficient ethyl levulinate production from furfural alcohol

Bifunctional ZnxMoy-TiO2 were prepared through sol-gel methodology for efficient furfuryl alcohol (FAL) alcoholysis to ethyl levulinate (EL). From the comprehensive analysis, the abundant Brønsted and Lewis acidity distribution, enhanced reducibility ability, and the synergistic effect between Zn and Mo were found in Zn1Mo1–TiO2. Specially, Zn played an important role in enhancing acidity strength and reducibility from NH3-TPD and H2-TPR profiles, whereas Mo exhibited the highest FAL adsorption capacity. The simulative structure with the adjacent Zn–Mo and non-adjacent Zn–Mo with O vacancies in TiO2 showed no difference in FAL adsorption energy and bader charge transfer capacity. After optimization, Zn1Mo1–TiO2 exhibited the highest FAL conversion (98 %) and EL yield (80 %) with negligible 2-(ethoxymethyl)furan (EMF) and 5-ethoxy-5-(ethyl-oxidaneylidene) pentan-2-one (intermediate 4) yield under optimum condition (50 mg Zn1Mo1–TiO2, 170 °C, 7 h). Most importantly, the catalyst recyclability was performed in continuous flow until 700 min without obvious EL yield decrease. The rational design of the cost-effective bimetallic based TiO2 will drive the green and efficient EL production in industrial scale.

Influence of 0.25% Indium Addition to Ni/CeO2 Catalysts for Dry Reforming of Methane

In this study, the surface and textural properties as well as the catalytic performance of Ni/CeO2 and NiIn/CeO2 catalysts prepared by wet impregnation (WI) and deposition–precipitation (DP) are investigated. The addition of Ni (3.0 wt.%) resulted in a decrease in the specific surface area and pore volume in the case of the WI method, possibly due to a blockage of mesopores. A minimal addition of In (0.25 wt.%) caused a further decrease in the surface area in both cases. XRD analysis showed that Ni deposited on CeO2 by DP resulted in some lattice incorporation, affecting the crystallinity of the support. The H2-TPR profiles altered depending on the different ways of Ni and In introduction. STEM-EDS-derived elemental maps indicated that the Ni and NiIn particles deposited on CeO2 using the DP method were somewhat smaller than in the WI synthesis. A comprehensive CO-DRIFTS analysis proved a direct Ni-In interaction in bimetallic samples, leading to the formation of a surface NiIn alloy. Ni/CeO2 catalysts showed a higher activity in the process of dry reforming of methane (DRM) than the bimetallic counterparts at 650 °C, with the Ni_DP sample performing slightly better. However, the Ni_DP catalyst showed significant coking, which was drastically reduced by the addition of In. The agglomeration of Ni and/or NiIn particles during the 6 h DRM reaction somewhat impaired the catalyst performance. Overall, this study highlights the intricate relationship between the catalyst preparation, surface properties and catalytic performance in the DRM reaction and emphasizes the beneficial role of In addition in reducing the coking of the monometallic catalyst and the critical location and surface morphology of nickel nanoparticles decorated with indium and in contact with ceria.

Modeling the temperature-programmed reduction of metal oxide catalysts by considering the particle-size distribution effect

Hydrogen temperature-programmed reduction (H2-TPR) has become a very useful and common technique for the chemical characterization of solids as it is sensitive to the study of reducible species in catalysis and is considered to be a fingerprint for the reducibility of metal oxide catalysts. However, although modeling of H2-TPR patterns has been extensively studied, little attention has been paid to the effect of particle-size distribution (PSD). The complexity of modeling H2-TPR patterns arises from the fact that the chemistry of metal oxide reduction depends on several factors, including particle size, nature of the support material and confinement within the porous structure, amongst others. In order to identify the kinetic reaction model governing the reduction of certain metal oxides and to explore the effect of PSD, pure metal oxides that only exhibited the particle size difference effect were used to model the H2-TPR patterns. Kinetic and thermodynamic data, which are very useful for characterizing heterogeneous catalysts, were obtained from this study. This work presents a simple procedure for modeling H2-TPR patterns of various metal oxides (i.e., CuO, Ag2O, and NiO) used as active phases in several reactions of environmental and energetic interest using several solid-state reaction kinetic models and considering their PSDs. The results obtained show that modeling the H2-TPR profiles provides information regarding the PSD of metal oxide catalysts that undergo a single-step reduction and only present the particle size difference effect.

Improvement of CO Oxidation and CH4 Combustion by Pd and Pt Partial Substitution on LaMn0.5Cu0.5O3 Perovskite.

LaMn0.5Cu0.5O3 (LMC) as the parent perovskite and Pd- and Pt-doped LaMn0.5Cu0.5O3 catalysts (LMCPd and LMCPt) instead of Cu were synthesized in a new solid-state synthesis technique at a low temperature. Perovskite lattice formation of the LMC catalyst was successfully performed at 600 °C. All perovskites were investigated by X-ray diffraction, HRTEM, O2-TPD, H2-TPR, BET, and XPS analyses. The prepared perovskites were used as heterogeneous catalysts for CO oxidation and methane combustion reactions. The catalytic performance of the LMC catalyst was noticeably enhanced via Pd and Pt substitution instead of Cu. The enhancement in the mobility of lattice oxygen and specific surface area has triggered this catalytic performance improvement, which play an important role in CO oxidation and methane combustion. The Mn 2p and Mn 3s XPS spectra showed that by doping Pd and Pt in the LMC perovskite, Mn was affected in different states and the Mn 3s peaks were only observed in the LMCPt catalyst. XPS spectra of the LMCPd1 sample showed a high oxidation state of Pd3+ or Pd4+, from which it can be concluded that Pd was successfully incorporated into the LMC perovskite lattice. The H2-TPR profiles of the LMCPd and LMCPt perovskites revealed that the reduction peaks of Cu and Mn were shifted to lower temperatures by increasing Pd and Pt partial substitution due to the synergetic effect of the cation and the H2-spillover effect of palladium and platinum.

Enhanced methane combustion and CO oxidation with Pd and Pt substitution LaSrCuO4 perovskites

The LaSrCuO4 as parent perovskite purely lattice was synthesized by new presented solid states technique and Pd and Pt substitution in LaSrCuO4 catalysts instead of Cu were prepared in this method at low temperature. All the perovskites were investigated by X-ray Diffraction, HRTEM, O2-TPD, H2-TPR, BET and XPS analyses. The CO oxidation and methane combustion catalytic activity of prepared perovskites were investigated which the LaSrCuO4 catalytic performance noticeably enhanced via Pd and Pt substitution instead of Cu. Both Langmuir and intra-facial mechanisms were intensified with increasing of surface area and mobility of lattice oxygen due to Pd and Pt doping in CO oxidation and methane combustion reactions. Pd 3d3/2 and 3d5/2 XPS spectra in LaSrCu0.9Pd0.1O4 confirmed Pd incorporation in perovskite structure due to presence of high oxidation state of Pd3+ or Pd4+. Pt 4 f5/2 and 4 f7/2 peaks approved Pt4+ oxidation state in LaSrCu1−xPtxO4 (x = 0.1,0.2) catalysts. The H2-TPR profiles of the Pt and Pd doped LSC perovskites revealed that the reduction peaks of the Cu were shifted to lower temperatures by increasing in Pd and Pt partial substitution due to H2-spillover effect of palladium and platinum.

Crystal-Plane-Dependent Guaiacol Hydrodeoxygenation Performance of Au on Anatase TiO2

TiO2-supported catalysts have been widely used for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about the effect of their different crystalline surfaces on their activity during the hydrodeoxygenation process. In this work, Au supported on anatase TiO2, mainly exposing 101 or 001 facets, was investigated for the hydrodeoxygenation (HDO) of guaiacol. At 300 °C, the strong interaction between the Au and TiO2-101 surface resulted in the facile reduction of the TiO2-101 surface with concomitant formation of oxygen vacancies, as shown by the H2-TPR and H2-TPD profiles. Meanwhile, the formation of Auδ−, as determined by CO-DRIFT spectra and in situ XPS, was found to promote the demethylation of guaiacol producing methane. However, this strong interaction was absent on the Au/TiO2-001 catalyst since TiO2-001 was relatively difficult to be reduced compared with TiO2-101. The Au on TiO2-001 just served as the active site for the dissociation of hydrogen without the formation of Auδ−. The hydrogen atoms spilled over to the surface of TiO2-001 to form a small amount of oxygen vacancies, which resulted in lower activity than that over Au/TiO2-101. The catalytic activity of the Au/TiO2 catalyst for hydrodeoxygenation will be controlled by tuning the crystal plane of the TiO2 support.

Enhanced redox properties of Gd-doped CeO2–TiO2 induced by oxygen vacancies and disordered structure

The redox properties of Gd-doped CeO2–TiO2 (xGd = 0.03, 0.09, and 0.15) was related to the oxygen defects and the local atomic structure. As the gadolinium doping concentration increased, a low-angle shift of the CeO2 (111) peak was observed. The EPR spectrum of the gadolinium-doped sample had an oxygen vacancy peak, indicating the oxygen vacancies induced by gadolinium. The O 1s core-level spectra showed that the ratio of oxygen vacancies gradually increased with the gadolinium doping concentration, and the Gd 4d and Ce 3d core-level spectra showed that Gd3+ reduced Ce4+ to Ce3+. An EXAFS analysis of the local atomic structures around Ce and Gd showed an increase in the Ce–O and Ce-(Ce,Gd) bond lengths and peak broadening occurred upon gadolinium doping, indicating bond disordering. The same Ce–O and Gd–O bond lengths suggested that the gadolinium was substituted for the cerium site. Surface chemisorption characterization was carried out by analyzing O2-TPD and H2-TPR profiles: the peaks for oxygen desorption and hydrogen reduction gradually shifted to lower temperatures as the dopant concentration increased. The quantities of desorbed oxygen and reduced hydrogen also increased. These enhanced redox properties resulted from disordered Ce3+-VO∙∙-Gd3+ acting as a surface active site, which promoted the redox reaction.

Stepwise conversion of methane to methanol over Cu-mordenite prepared by supercritical and aqueous ion exchange routes and quantification of active Cu species by H2-TPR

Copper-exchanged mordenite prepared by supercritical ion exchange (SCIE) and aqueous ion exchange (AIE) were investigated in stepwise conversion of methane to methanol. Increasing the oxygen activation temperature and methane reaction time enhances the methanol yield of copper-exchanged mordenite prepared by SCIE (Cu-MORS). The reducibility of Cu-MORS was compared with those of Cu-MORA prepared by aqueous ion exchange (AIE) using H2-TPR. It was demonstrated for the first time that deconvoluted H2-TPR profile coupled with effects of Cu loading and oxygen activation temperature on methanol yield data can be used to distinguish the active Cu sites from inactive ones based on their reduction temperature. The copper species responsible for methane activation were found to be reduced below 150 °C by H2 in both Cu-MORS and Cu-MORA. From the stoichiometry of the reaction of H2 with Cu2+ species, the average number of copper atoms of active sites were calculated as 2.07 and 2.80 for Cu-MORS and Cu-MORA, respectively. Differences in structure of copper species caused by the synthesis routes were also detected by in-situ FTIR upon NO adsorption indicating a higher susceptibility of Cu-MORS towards autoreduction. The results demonstrated the potential of TPR based methods to identify copper active sites and suggested the importance of site selective ion exchange in order to controllably synthesize active Cu species in zeolites.

Synthesis of novel Co(3-x)MnxO4@TiO2 core-shell catalyst for low-temperature NH3-SCR of NOx with enhanced SO2 tolerance

In this study, the Co(3-x)MnxO4@TiO2 core-shell catalysts prepared by sol-gel and external kinetic coating method were investigated for DeNOx by response surface methodology (RSM) using 3-factor with 5-level experiments. Compared with CoMn2O4 sample, the CoMn2O4@TiO2 catalyst was optimized to obtain almost 100% NOx conversion at 125°C to 225°C that also maintained above 80% SCR activity with 100 ppm SO2 and 10 vol.% H2O in the testing time within 24 h. The XRD and Raman show a clear distinction of that CoMn2O4 spinel phase was well-dispersed on anatase TiO2 over CoMn2O4@TiO2 catalyst, which exhibited a core-shell structure with obvious distribution boundary of CoMn2O4 core coated by TiO2 shell confirmed by TEM images. This intact catalyst presented complete TiO2 coating structure due to the detected bonds Mn-O, Co-O and particular Ti-O via FT-IR analysis. NH3-TPD and H2-TPR profiles indicated that the CoMn2O4@TiO2 catalyst owned more acid sites, stronger acidity and enhanced redox capacities benefiting from its core-shell structure after TiO2 coating. According to XPS analysis, higher content of (Mn3++Mn4+)/(Mn2++Mn3++Mn4+) (77.7%), Co3+/ (Co2+ + Co3+) (53.5%) and surface oxygen (26.1%) were in favour of valence electron interaction (Mn4++Co2+↔Mn3++ Co3+, Mn3++Ti4+↔Mn4++ Ti3+). The NH3-SCR reaction pathways over CoMn2O4 and CoMn2O4@TiO2 catalysts were compared and proposed through DRIFTS experiments, which mainly follows the typical Eley-Rideal (E-R) mechanism, while the Langmuir-Hinshelwood (L-H) mechanism is weak at 225 °C. This study opens up a new avenue for designing efficient and environment-friendly NH3-SCR catalysts and looks promising for practical application.

Insights into the Redox Behavior of Pr0.5Ba0.5MnO3−δ-Derived Perovskites for CO2 Valorization Technologies

In situ temperature-programmed (TP) analyses in a multianalytical approach including X-ray diffractometry (XRD), temperature-programmed reduction (TPR), thermogravimetry (TGA), near-edge X-ray absorption fine structure spectroscopy (NEXAFS) are used to study the relationship between redox properties and structural changes in Pr0.5Ba0.5MnO3−δ (m-PBM), PrBaMn2O5+δ (r-PBM), and PrBaMn2O6−δ (o-PBM) when exposed to reduction/oxidation cycles. TP-XRD analysis shows that under reducing conditions, between 300 and 850 °C, the biphase perovskite m-PBM turns into the monolayered perovskite r-PBM. Stabilization of the latter phase at room temperature requires early oxidation in air at a high temperature (850 °C) to avoid segregation, resulting in the formation of the oxidized layered phase (o-PBM). The o-PBM layered perovskite is characterized by the H2-TPR profile, showing two reduction peaks at temperatures below 500 °C. TP-NEXAFS characterization reveals the copresence of Mn(IV) (60%), Mn(III) (30%), and Mn(II) (10%) and helps to interpret the reduction profile: Mn(IV) converts to Mn(III) at ∼300 °C (I pk), Mn(III) to Mn(II) at ∼450 °C (II pk). The TGA characterization confirms the reversibility of the o-PBM ↔ r-PBM process at 800 °C; in addition, it shows that the r-PBM can be oxidized almost completely (∼99%) also by CO2 without accumulation of carbonates. This study sheds light on the peculiar redox behavior of PBM-based materials and paves the way for their application as oxygen carriers and catalytic promoters in different CO2 enhancement technologies. Here, we discuss the results obtained to develop versatile and redox-resistant electrodes for solid oxide electrochemical cell/solid oxide fuel cell applications.

Enhanced catalytic oxidation of diluted ethylene oxide on Pt/CeO2 catalyst under low temperature

A thorough catalytic combustion toward diluted ethylene oxide (EO) is demonstrated. The Pt active phase and CeO2 support were selected to introduce a synergistic effect. As a result, a superior catalytic activity and less severe coking trend were observed on the Pt/CeO2 catalyst when compared with another widely-used Pt/Al2O3 catalyst. The XPS spectra and H2-TPR profiles evidenced that the Pt/CeO2 catalyst has both stronger metal-support interaction and more abundant oxygen vacancies, which is believed at the heart of its excellent performance. Finally, the degradation pathways of EO were explored by in-situ DRIFTS. The weak H2O affinity of Pt/CeO2 catalyst can inhibit the polycondensation reaction and result in the favorable degradation of EO. In contrast, abundant hydroxyl species were present on the hydrophilic Pt/Al2O3 catalyst surface, which may serve as acid sites and complicate the EO degradation, and therefore various side products and carbon deposits would appear in this case.

Promoting effect of Rh-impregnation on Ag/CeO2 catalyst for soot oxidation

In this study, the effect of Rh on the catalytic properties of CeO2 was examined using a series of Rh-impregnated catalysts with different Rh loadings (Rh(x)Ce, x = 1, 2, 3, 5 wt%). The Rh species were highly dispersed over CeO2, and Rh(x)Ce exhibited higher soot oxidation activity than CeO2. In particular, the H2-TPR and O2-TPD profiles of the prepared catalysts indicated that Rh(2)Ce outperformed all other Rh(x)Ce catalysts owing to its high reducibility and desorption of active oxygen species at low temperatures. Moreover, an excessive Rh loadings resulted in an increase in the Rh3+/Rh0 and a decrease in the surface oxygen reducibility of the Rh(x)Ce catalysts. Subsequently, the promoting effect of Rh on the catalytic properties of Ag/CeO2 was evaluated using a Rh-impregnated Ag/CeO2 catalyst (Rh(2)Ag(5)Ce). The Rh species were well-dispersed over Ag/CeO2, and Rh(2)Ag(5)Ce presented a higher catalytic activity than the Ag/CeO2 catalyst. XPS analysis revealed that the interaction between Rh and Ag caused changes in the electronic states of Rh and Ag. Moreover, the soot-TPR and Raman spectra data revealed that the Rh(2)Ag(5)Ce catalyst could use active oxygen species at a lower temperature and generate a higher amount of reactive oxygen species than all other analyzed catalysts. Furthermore, macroporous Rh(2)Ag(5)Ce exhibited excellent activity, which was ascribed to the high soot-catalyst contact efficiency.

Epoxidation of propane with oxygen and/or nitrous oxide over silica-supported vanadium oxide

Propane to propene oxide (PO) oxidation over V-containing mesoporous silica of SBA-3 structure has been studied using different oxidants (nitrous oxide, oxygen, and their mixture) in the temperature range 673–773 K. Electron spin resonance spectroscopy, ultraviolet–visible spectroscopy, and X-ray photoelectron spectroscopy (XPS), as well as X-ray diffraction, temperature-programmed reduction with hydrogen (H2 TPR), and low-temperature N2 adsorption/desorption, were applied for characterization of fresh and spent catalysts. XPS spectra and H2 TPR profiles revealed a significant reduction of V-species as a result of propane oxidation with N2O alone, which leads to a decrease in both propane conversion and the space–time yield (STY) of PO. The use of an N2O–oxygen mixture as an oxidant of propane allows the vanadium valence to be stabilized at a level similar to the initial sample, which results in stable activity with time on stream. Propane conversion of 40%, propylene selectivity of 45%, and propylene oxide selectivity of 11%, corresponding to a STY of propylene oxide of about 15 g kgcat-1h−1, have been obtained, which makes these results very promising compared with the data reported in the literature. Vanadium catalyst used with only oxygen results in stable propane conversion with high total oxidation and stable propene selectivity, although the STY of PO is 10 times lower. N2O applied as the only oxidant results in rapid catalyst deactivation, and after 2 h on stream, STY of PO is only 2.5 g kgcat-1h−1.

Catalytic activity, selectivity, and stability of co-precipitation synthesized Mn-Ce mixed oxides for the oxidation of 1,2-dichlorobenzene.

Mn-Ce mixed oxides were prepared using a simple, facile, and high yielding co-precipitation method. The effects of the proportion of Mn/Ce and the addition of Fe, Co, Sn on the physical and chemical properties of catalysts have been thoroughly investigated. Several analytical techniques were conducted, namely BET, XRD, SEM, XPS, and H2-TPR. Compared with other catalysts, MCFe shows the highest specific surface area of 108.2 m2/g and Dp of 7.2 nm. The XRD results indicated that the diffraction peaks were dominated by Mn2O3, the pyrolusite MnO2, and hausmannite Mn3O4. SEM observations showed nanoparticle and plate-like structures. XPS analysis indicated that there is electron exchange between both Mn3+ and Mn4+ as well as Ce3+ and Ce4+ which promotes catalytic oxidation. The H2-TPR profiles displayed two dominant peaks located around 250 °C and 310 °C. Catalytic activity, selectivity, and stability of co-precipitation synthesized Mn-Ce mixed oxides for the oxidation of 1,2-dichlorobenzene were tested. The selectivity of MCFe towards CO2 and CO reached 96 % at 270 °C. At 180 °C, MCFe had the optimum stability with a removal efficiency of about 50 %. At last, the main byproducts were identified by GC-MS. Possible reaction paths were proposed. The Mn-Ce mixed oxides catalysts may be a more economical alternative for industrial application.

Methane oxidation by N2O over Fe-FER catalysts prepared by different methods: Nature of active iron species, stability of surface oxygen species and selectivity to products

Catalysts with different iron species distributions were developed by loading iron ions to ferrierite (FER) zeolite using liquid ion exchange (IE) and solid state ion exchange (SSIE) methods, which in turn facilitates to study the relation between the nature of iron sites with the formation and stability of surface oxygen species, based on the comparable investigation of catalytic activity and selectivity to products over the catalysts, and the characterisation results obtained from a variety of spectroscopic and solid characterization techniques.IR spectra and NH3-TPD profiles demonstrate a greater extent of exchange of protons in bridging OH positions by iron cations with the Fe-FER-SSIE, in comparison to Fe-FER-IE catalyst. The primary catalytic species present in Fe-FER-IE are isolated Fe species in cation exchange positions, as indicated by UV–vis spectra, while isolated and oligomeric extra-framework Fe species were present in Fe-FER-SSIE catalysts, which is consistent with H2-TPR profiles of N2O pre-treated catalysts and IR spectra of NO adsorption on the catalysts. N2O-TPD results demonstrate that the desorption of oxygen molecules (O2) released from surface oxygen species was observed at lower temperature and higher concentration from Fe-FER-IE than Fe-FER-SSIE. Higher ratio of N2O consumption/methane conversion over Fe-FER-IE was observed than Fe-FER-SSIE. With similar methane conversion, over Fe-FER-SSIE a higher selectivity to valuable products methanol, formaldehyde and dimethyl ether was observed than over Fe-FER-IE.

Essential role of B metal species in perovskite type catalyst structure and activity on toluene oxidation

The perovskite type materials with transition metals are getting more attention especially as catalysts in total oxidation reaction. This work explores the B metal effect on the catalytic activity of LaBO3 structured perovskites in total oxidation of toluene. The perovskite type oxides were obtained by Pechini method and characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, thermogravimetric analysis and differential scanning calorimetry, temperature-programmed reduction (H2-TPR), Raman spectroscopy, Fourier transform infrared spectroscopy and particle size analysis. The results showed that LaFeO3 catalyst contained a single orthorhombic LaFeO3 phase, while LaMnO3 contained LaMn2O5 species besides cubic LaMnO3 phase. Both catalysts show very narrow distributions and average values of 55.59 μm and 51.43 μm for LaMnO3 and LaFeO3, respectively. With regard to the H2-TPR profile for the LaMnO3, Mn4+ to Mn3+ reduction and Mn3+ to Mn2+ reduction. Consequently, the redox performance of ABO3 perovskites was found as mainly driven by the B-site transition-metal element character. According to the catalytic tests, the LaMnO3 catalyst was more active for toluene oxidation than LaFeO3 and achieved the lowest light-off temperatures. An excellent agreement between the experimental data and the proposed one-dimensional pseudo-homogeneous model was achieved and corresponding kinetic parameters (estimated rate constants, k, activation energies, EA, and frequency factors, Ar) were estimated. Lower activation energy was estimated for LaMnO3 catalyst (84 kJ mol−1 vs. 99 kJ mol−1 for LaFeO3) confirming that LaMnO3 catalyst was more active for toluene oxidation under reaction conditions presented in this paper.

Catalytic performance of Ni/CaO-Ca12Al14O33 catalyst in the green synthesis gas production via CO2 reforming of CH4

Dry Reforming of Methane over 15wt.% Ni/CaO-Ca12Al14O33 catalyst was performed in a microreactor in the temperature range 600−800°C under atmospheric pressure, at WHSV of 120 Lg−1h−1 and by time on stream of 12 h for producing synthesis gas. The novel catalyst was prepared by Ni wet impregnation of a mixed calcium-aluminum-oxide (CAO) ceramic support. Similarly, a Ni/γ-Al2O3 reference catalyst was prepared. Characterizations were conducted by TGA-FTIR, XRD, SEM-EDS, N2 physisorption, H2-TPR, CO2-TPD, and CO2-TPRn techniques. After calcination(500°C)/reduction(700°C) steps in situ formed CaO promoter was highly dispersed on Ca12Al14O33 carrier, which induced strong basicity. A good anchorage of NiO on CAO support was evidenced by reduction peaks at 490°C and 650°C on the H2-TPR profile. The reduced mesoporous catalyst presented high SBET, large pores volume, and unimodal pore size distribution. High reactants conversions, good H2 and CO selectivity, and H2/CO molar ratio close to unity at 800°C were achieved. Although the catalytic activity of Ni/γ-Al2O3 reference catalyst was slightly better than that of Ni/CaO-Ca12Al14O33 catalyst the stability was worse owing to the excessive carbon build-ups, whereas the novel catalyst displayed a very low carbon deposit on spent catalyst at 600 and 700°C, and negligible coke deposit at 800°C. It was established that the basicity of CaO-Ca12Al14O33 support can play a key role in preventing coke deposition during DRM. The Ni CaO-Ca12Al14O33 can serve as sorbent for CO2 capture and simultaneously for its catalytic conversion in a valuable fuel.

Phenomenological approaches for quantitative temperature-programmed reduction (TPR) and desorption (TPD) analysis

Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) are techniques widely used for catalyst characterization, providing information about active sites. However, results from these experiments are usually interpreted with the aid of empirical models, based on the representation of reduction or desorption profiles as summations of empirical reference curves. In this context, phenomenological approaches can present several advantages over this traditional empirical approach, as in this case the extracted information can be based on theoretical models that allows for a deeper understanding of the catalyst properties. For this reason, in the present work, empirical and phenomenological modelling approaches are evaluated for the quantitative analysis of H2-TPR and NH3-TPD profiles, obtained from the characterization of Ni/SiO2 and Al2O3 alumina catalysts, respectively, and results from both approaches are thoroughly compared and discussed for the first time. Our results, obtained from the fitting of both modelling approaches to the whole experimental profile by using nonlinear regression, indicate that the phenomenological modelling approach can be considered better and should therefore be preferred, as it allows for significantly more accurate quantification and correct discrimination of distinct active sites, in addition to simultaneously enabling the determination of reduction or desorption kinetics parameters.

CO2 reforming of methane over Ni and/or Ru catalysts supported on mesoporous KIT-6: Effect of promotion with Ce

CO2 reforming of methane was studied over Ni and/or Ru supported on KIT-6 and KIT-6 promoted with Ce catalysts synthesized using the wet impregnation technique. The percent of nickel and ruthenium in all catalysts was fixed at 15 wt% and/or 1 wt% respectively. All catalysts were calcined at 550 °C and characterized by XRD, N2 adsorption/desorption, H2-TPR and CO2-TPD. All catalysts exhibited type IVa isotherms attributed to their mesoporous nature. Ce promotion resulted in a significant destruction of the porous structure which was demonstrated by the change in the shape of the isotherm as well as decreased surface areas and pore volumes. H2-TPR profiles showed reduction peaks corresponding to the reduction of agglomerated RuO2 species as well as different NiO species that are either free or in interaction with the support. It was noticed that the incorporation of Ce impaired the interactions between the active phase and the support. CO2-TPD profiles demonstrated that promoting the catalysts with Ce increased their basicity. Among the non-promoted catalysts, Ni-Ru/KIT-6 presented enhanced active phase dispersion, reducibility, and the highest basicity which resulted in an ameliorated catalytic performance. However, the promoted Ni-Ru/Ce-KIT-6 catalyst exhibited much higher activity and stability after 12 h on stream despite the formation of graphitic carbon resulting from the decomposition of methane.

Fischer-Tropsch synthesis to lower α-olefins over cobalt-based catalysts: Dependence of the promotional effect of promoter on supports

Promoters, such as Na and Mn, play an important role in governing the active phase and catalytic performance of cobalt-based FTS catalyst. In this work, the dependence of the promotional effect of promoters on supports has been investigated by using the carbon and silica supported cobalt-based catalysts in the presence of Na, Mn, and both Na and Mn promoters, respectively. The characterization results of H2-TPR, CO-TPD and XRD profiles together with the FTS performances demonstrate the strong dependence of the promotional effect of promoter on the type of support used. The carbon support, which shows weak cobalt-support interaction, facilitates the manifestation of the effect of promoter. In detail, Mn can promote the formation of Co2C sites at the conditions of 260 °C, 0.5 MPa and lower H2/CO ratio, resulting from the promoted CO adsorption and subsequent dissociation. Thus, the suppressed adsorption of H2 and the promoted surface dissociative C* concentration enhances the selectivities to lower olefins (C2=-C4=) and C5+ with a decrease in methane selectivity. Interestingly, the further addition of Na promoter shows synergistic effect of Na and Mn promoter on remarkably increasing selectivity to lower olefins due to the obviously suppressed chain growth. This synergistic effect could be observed only at the weak cobalt-carbon interaction with a more obvious effect at lower H2/CO ratio in feed gas that favors the increase of Co2C sites with mainly exposed facets of (111) and (020). The presence of (020) facet might be more crucial to enhance the formation of lower olefins. However, over silica support with strong cobalt-silica interaction, the promotional effect of Mn is obviously suppressed, which leads to only CoO and metallic Co sites in the FTS reaction and much weaker impact on product selectivity. The further addition of Na into Mn-promoted cobalt catalysts shows similar effect as Na promoter alone in the product selectivity where the chain growth is highly promoted to remarkably suppress methane selectivity and enhance selectivity to C5+ rather than desired lower olefins. In contrast to carbon support, the strong cobalt-silica interaction leads to less promotional formation of CO2 via the Boudouard reaction (2CO*→C* + CO2) due to the increased non-dissociative adsorption of CO.