NH3 Temperature-programmed Desorption Research Articles

Novel Method for Preparing Controllable Nanoporous a-Fe2O3 and its Reactivity to SCR De-NOx

ABSTRACTControllable nanoporous hematite (CNH, α-Fe2O3) was prepared by thermal treatment of α-FeOOH at different temperatures, and the SCR activity of the prepared α-Fe2O3 was evaluated. XRD (X-ray diffraction), HRTEM (high-resolution transmission electron microscopy), N2 adsorption-desorption, XPS (X-ray photoelectron spectroscopy), and NH3-TPD (NH3-temperature programmed desorption) were utilized to characterize the catalysts. The results indicated that after thermal treatment at less than 600°C, the α-Fe2O3 catalysts exhibited excellent NO conversion that was higher than 80% in a temperature range from 300 to 400°C. CNH400 with a relatively large surface area of 47.24 m2 g–1 and many surface hydroxyl groups did not exhibit a substantially improved SCR activity even though it exhibited the best SCR activity. Therefore, the L-H mechanism was not the main reaction route for SCR of NO by α-Fe2O3. The increasing crystallization of α-Fe2O3 decreased the SCR activity, indicating that a decrease in surface oxygen defects was important for the SCR of NO and fitting the E-R mechanism. The NH3-TPD and XPS (O1s) results confirmed this hypothesis. This study provides an approach for the design and preparation of a controllable nanoporous α-Fe2O3 catalyst for SCR of NO by NH3.

Effect of Calcination Temperatures and Mo Modification on Nanocrystalline (γ-χ)-Al2O3 Catalysts for Catalytic Ethanol Dehydration

The mixed gamma and chi crystalline phase alumina (M-Al) catalysts prepared by the solvothermal method were investigated for catalytic ethanol dehydration. The effects of calcination temperatures and Mo modification were elucidated. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), and NH3-temperature programmed desorption (NH3-TPD). The catalytic activity was tested for ethylene production by dehydration reaction of ethanol in gas phase at atmospheric pressure and temperature between 200°C and 400°C. It was found that the calcination temperatures and Mo modification have effects on acidity of the catalysts. The increase in calcination temperature resulted in decreased acidity, while the Mo modification on the mixed phase alumina catalyst yielded increased acidity, especially in medium to strong acids. In this study, the catalytic activity of ethanol dehydration to ethylene apparently depends on the medium to strong acid. The mixed phase alumina catalyst calcined at 600°C (M-Al-600) exhibits the complete ethanol conversion having ethylene yield of 98.8% (at 350°C) and the Mo-modified catalysts promoted dehydrogenation reaction to acetaldehyde. This can be attributed to the enhancement of medium to strong acid with metal sites of catalyst.

One-step post-synthesis treatment for preparing hydrothermally stable hierarchically porous ZSM-5

Hierarchically porous ZSM-5 (SiO2/Al2O3 ≈ 120) containing phosphorus was prepared by a one-step post-synthesis treatment involving controlled desilication and phosphorous modification. The hierarchically porous ZSM-5 featured high thermal and hydrothermal stability. The obtained ZSM-5 zeolites were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, NH3 temperature-programmed desorption, and 27Al and 31P magic-angle spinning nuclear magnetic resonance spectroscopy. The prepared ZSM-5 displayed enhanced activity and prolonged lifetime toward hydrocarbon cracking. The high activity was attributed to improved coke tolerance owing to the presence of the highly stable mesoporous network of ZSM-5 and acid sites introduced upon phosphorus modification. Additionally a mechanism of the stabilization of the zeolites by phosphorus was proposed and discussed.

Enhancing hydrothermal stability of nano-sized HZSM-5 zeolite by phosphorus modification for olefin catalytic cracking of full-range FCC gasoline

In this study, phosphorus modification by trimethyl phosphate impregnation was employed to enhance the hydrothermal stability of nano-sized HZSM-5 zeolites. A parallel modification was studied by ammonium dihydrogen phosphate impregnation. The modified zeolites were subjected to steam treatment at 800 °C for 4 h (100% steam) and employed as catalysts for olefin catalytic cracking (OCC) of full-range fluid catalytic cracking (FCC) gasoline. X-ray diffraction, N2 physical adsorption and NH3 temperature-programmed desorption analysis indicated that, although significant improvements to the hydrothermal stability of nano-sized HZSM-5 zeolites can be observed when adopting both phosphorus modification strategies, impregnation with trimethyl phosphate displays further enhancement of the hydrothermal stability. This is because higher structural crystallinity is retained, larger specific surface areas/micropore volumes form, and there are greater numbers of surface acid sites. Reaction experiments conducted using a fixed-bed micro-reactor (catalyst/oil ratio = 4, time on stream = 4 s) showed OCC of full-range FCC gasoline—under a fluidized-bed reaction mode configuration—to be a viable solution for the olefin problem of FCC gasoline. This reaction significantly decreased the olefin content in the full-range FCC gasoline feed, and specifically heavy-end olefins, by converting the olefins into value-added C2–C4 olefins and aromatics. At the same time, sulfide content of the gasoline decreased via a non-hydrodesulfurization process. Nano-sized HZSM-5 zeolites modified with trimethyl phosphate exhibited enhanced catalytic performance for OCC of full-range FCC gasoline.

Diethyl Ether Production during Catalytic Dehydration of Ethanol over Ru- and Pt- modified H-beta Zeolite Catalysts.

In the present study, the catalytic dehydration of ethanol over H-beta zeolite (HBZ) catalyst with ruthenium (Ru-HBZ) and platinum (Pt-HBZ) modification was investigated. Upon the reaction temperature between 200 and 400°C, it revealed that ethanol conversion and ethylene selectivity increased with increasing temperature for both Ru and Pt modification. At lower temperature (200 to 250°C), diethyl ether (DEE) was the major product. It was found that Ru and Pt modification on HBZ catalyst can result in increased DEE yield at low reaction temperature due to increased ethanol conversion without a significant change in DEE selectivity. By comparing the DEE yield of all catalysts in this study, the Ru-HBZ catalyst apparently exhibited the highest DEE yield (ca. 47%) at 250°C. However, at temperature from 350 to 400°C, the effect of Ru and Pt was less pronounced on ethylene yield. With various characterization techniques, the effects of Ru and Pt modification on HBZ catalyst were elucidated. It revealed that Ru and Pt were present in the highly dispersed forms and well distributed in the catalyst granules. It appeared that the weak acid sites measured by NH3 temperature-programmed desorption technique also decreased with Ru and Pt promotion. Thus, the increased DEE yields with the Ru and Pt modification can be attributed to the presence of optimal weak acid sites leading to increased intrinsic activity of the catalysts. It can be concluded that the modification of Ru and Pt on HBZ catalyst can improve the DEE yields by ca. 10%.

The effects of MxOy (M = K, Ba, and Sr) promoters on inhibiting carbon deposit during catalytic cracking reactions

The study involved a Pt/ZrO2-TiO2-Al2O3 catalyst (PZTA) modified by MxOy (M=K, Ba and Sr) promoters to inhibit the formation of carbon deposit during catalytic cracking reactions. It was found that Sr-PZTA showed the least carbon deposit (5.22mg/cm2), highest gas yield (20.05%) and heat sink (2.70MJ/kg). Moreover, the catalysts before and after modification were characterized by N2 adsorption-desorption measurement, X-ray diffraction (XRD), NH3-Temperature programmed desorption (NH3-TPD), Pyridine-infrared spectroscopy (Py-IR), Temperature programmed oxidation (TPO), and Scanning electron microscopy (SEM). The results indicated that the addition of these promoters not only changed the strength and density of acid sites, but also regulated the amount of Brönsted and Lewis acid sites. After modification, more than 50% of the strong acid sites transformed to weak or/and medium acid sites. Meanwhile, the density of acid sites decreased from 4.5 to 4.0μmol/m2, leading the disproportionation reactions between adjacent carbeniums which are responsible for carbon deposit inhibited. In addition, the amount of Lewis acid sites decreased seriously and only 10% of Lewis acid sites kept over K-PZTA. The dehydrogenation reactions of forming unsaturated carbenium and carbon deposit were thus hindered. By contrast, the strong Brönsted acid sites which can accelerate the rate of cracking reactions over Ba-PZTA and Sr-PZTA increased. Both the spherical and spiral filament carbon deposit were detected on the surface of PZTA. However, the deposit over the modified catalysts mainly presented as agglomerates of spherical particles.

Propane dehydrogenation catalyzed by gallosilicate MFI zeolites with perturbed acidity

The propane dehydrogenation (PDH) behavior of gallosilicate MFI catalysts synthesized in the presence of 3-mercaptopropyl-trimethoxysilane (MPS) is investigated. MPS addition to the zeolite synthesis gel results in gallosilicate molecular sieves with reduced Brønsted acidity and enhanced Lewis acidity, as shown by combined NH3 temperature-programmed desorption (TPD), isopropylamine (IPA) TPD and IR analysis of pyridine-loaded catalysts. In particular, the gallosilicate MFI catalysts prepared using MPS provide a significant concentration of strong Lewis acid sites, which are important in controlling the selectivity of PDH. Enhanced PDH performance with higher propane conversion rates and improved propylene selectivity with limited cracking and aromatization products are obtained from the catalysts synthesized with MPS. The gallosilicate MFI materials prepared using MPS are compared with a benchmark chromia-alumina catalyst, and the gallosilicate materials have a lower rate of deactivation (>50% lower) but slightly inferior propylene selectivity (Ga-MFI: 75%; Chromia-Alumina: 85%).

Alkylation of toluene with tert-butyl alcohol over HPW-modified Hβ zeolite

An Hβ-supported heteropoly acid (H3PW12O40 (HPW)/Hβ) catalyst was successfully prepared by wetness impregnation, and investigated in the alkylation of toluene with tert-butyl alcohol for the synthesis of 4-tert-butyltoluene (PTBT). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fourier-transform infrared spectroscopy, inductively coupled plasma-optical emission spectrometry, the brunauer emmett teller (BET) method, temperature-programmed NH3 desorption, and pyridine adsorption infrared spectroscopy were used to characterize the catalyst. The results showed that loading HPW on Hβ effectively increased the B acidity and decreased the pore size of Hβ. The B acidity of HPW/Hβ was 142.97 μmol/g, which is 69.74% higher than that of Hβ (84.23 μmol/g). The catalytic activity of the HPW/Hβ catalyst was much better than that of the parent Hβ zeolite because of its high B acidity. The toluene conversion over HPW/Hβ reached 73.1%, which is much higher than that achieved with Hβ (54.0%). When HPW was loaded on Hβ, the BET surface area of Hβ decreased from 492.5 to 379.6 m2/g, accompanied by a significant decrease in the pore size from 3.90 to 3.17 nm. Shape selectivity can therefore play an important role and increase the product selectivity of the HPW/Hβ catalyst compared with that of the parent Hβ. PTBT (kinetic diameter 0.58 nm) can easily diffuse through the narrowed pores of HPW/Hβ, but 3-tert-butyltoluene (kinetic diameter 0.65 nm) diffusion is restricted because of steric hindrance in these narrow pores. This results in high PTBT selectivity over HPW/Hβ (around 81%). The HPW/Hβ catalyst gave a stable catalytic performance in reusability tests.

Lanthanide compounds as catalysts for the one-step synthesis of vinyl chloride from ethylene

The industrial manufacture of vinyl chloride relies on a two-step process involving CuCl2-catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. This work evaluates a wide range of commercial and self-prepared lanthanide (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) compounds for the one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623–773K and 1bar using feed ratios of C2H4:HCl:O2:Ar:He=3–6:1–9.6:1–7:3:80–92 and space times of 6–252ghmol−1 (based on ethylene). Ex situ characterization by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy reveals that the oxide forms of all compounds, except CeO2, transform into their respective (oxy)chloride. Among all studied systems, CeO2 shows the highest activity but suffers from combustion forming COx, while europium oxychloride (EuOCl) leads to the best vinyl chloride selectivity of 96% at 20% C2H4 conversion for over 100h on stream. Temperature-programmed reduction with H2, temperature-programmed desorption of NH3, and oxidation tests (C2H4, CO, and HCl oxidation) unravel the unique balance of mild redox and enhanced acid properties of EuOCl compared to CeO2, which suppress over-oxidation and boost ethylene dichloride dehydrochlorination. Strategies to couple the excellent selectivity of EuOCl with the high activity of CeO2 are demonstrated through the synthesis of homogeneous europium-cerium mixed oxides, combining two functions on a single surface. In addition, the engineering of a dual-bed reactor, integrating a CeO2 bed first to produce ethylene dichloride in high yield which is subsequently transformed to vinyl chloride over EuOCl leads to vinyl chloride yields of up to 30% per pass. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of rare-earth compounds in industrially-relevant reactions.

Vapor phase methylation of phenol on Fe-substituted ZrO2 catalyst

Fe-doped ZrO2 compounds were prepared by a co-precipitation method. The compounds were characterized by X-ray diffraction, N2 adsorption-desorption, ultraviolet diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, transmission electron microscopy, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and in situ Fourier transform infrared spectroscopy. The incorporation of Fe into ZrO2 lattice favored and effectively stabilized the formation of purely ZrO2 tetragonal phase. Subsequently, the catalytic activity of the Fe-doped ZrO2 compounds was evaluated toward vapor phase methylation of phenol. The catalytic activity was governed by Fe content and related to the Lewis acidity of the prepared catalyst.

Er/β-zeolite-catalyzed one-pot conversion of cellulose to lactic acid

Various Er/β-zeolite catalysts were prepared by grafting erbium species in aqueous solutions of erbium chloride onto β-zeolites. The catalysts were characterized using X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectroscopy, N2 physical adsorption, powder X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. These catalysts were evaluated in the one-pot hydrothermal conversion of cellulose to lactic acid. Lactic acid yields of approximately 58 % were obtained using an erbium grafted on de-aluminated β zeolite (Er/deAlβ-2) with an erbium content of 12.4 wt% and a Si/Al ratio of 159:1. In catalyst recycling tests, the lactic acid yield decreased from 57.9 % in the first cycle to 51.2, 49.8 and 49.6 % in the second, third and fourth cycles, respectively. The decreases in catalytic activity during recycling are proposed to arise mainly from a combination of erbium ion leaching, deposition of carbon species in the zeolite pores and the partial structure collapse.

Dehydration of bio-ethanol to ethylene over iron exchanged HZSM-5

Iron exchanged ZSM-5 with Si/Al ratio from 25 to 300 prepared by three consecutive ion exchanges was used for the dehydration of ethanol to ethylene. The iron exchanged ZSM-5 (Si/Al = 25) catalyst with an iron content of 0.46 wt% gave 97%−99% yield of ethylene at 98%−99% conversion of ethanol at 260 °C and 0.81 h−1 liquid hourly space velocity. The high performance was maintained for 60 d on-stream. X-ray diffraction, Fourier transform infrared spectroscopy of pyridine adsorption, NH3 temperature-programmed desorption and diffuse reflectance UV-vis spectroscopy were used for catalyst characterization. Ion exchange with iron decreased the total acidity of the zeolite, especially the strong acid sites and Brönsted acid sites. The doped iron species were distributed over Fe-ZSM-5 as predominantly isolated Fe3+. Therefore, the catalytic performance for ethanol dehydration to ethylene was improved.

Efficient ceria-zirconium oxide catalyst for carbon dioxide conversions: Characterization, catalytic activity and thermodynamic study

In this study, ceria-zirconia based catalysts (CeO2, ZrO2 and Ce0.5Zr0.5O2) were synthesized by hydrothermal method and characterized by N2-sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Acidity and basicity of synthesized catalysts were investigated by NH3 and CO2 temperature-programmed desorption (TPD). Brunauer-Emmett-Teller (BET) surface area of CeO2, Ce0.5Zr0.5O2 and ZrO2 were found to be 88, 117 and 70 m2 g−1 and average crystallite sizes was 9.48, 7.09 and 9.45 nm, respectively. These catalysts were further used for direct conversion of CO2 with methanol for the synthesis of dimethyl carbonate (DMC). DMC yield was found to be highly dependent upon the both basicity and acidity of catalysts. Ce0.5Zr0.5O2 catalysts showed better activity as compared to CeO2 and ZrO2 catalysts. Effect of reaction conditions (such as catalyst dose, reaction temperature and reaction time) and catalyst reusability was studied with Ce0.5Zr0.5O2 catalyst. The optimum operating condition for direct conversion of CO2 into DMC at constant pressure of 150 bar were found to be reaction time = 24 h, catalyst dose = 1.25 g and temperature = 120 °C. Moreover, chemical equilibrium modeling was performed using Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid (1PVDW) mixing rule to calculate the heat of reaction and Gibbs free energy change.

Effect of praseodymium additive on CeO2(ZrO2)/TiO2 for selective catalytic reduction of NO by NH3

A series of praseodymium added CeO2(ZrO2)/TiO2 catalysts separately prepared by methods of sol-gel and impregnation were tested for selective catalytic reduction of NO, and characterized by X-ray diffraction (XRD), N2-brumauer-emmett-teller (N2-BET), NH3-temperature programmed desorption (NH3-TPD), H2-temperature programmed reduction (H2-TPR), PL spectra, Raman spectra, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), respectively. Influence of preparation method on catalytic performance was studied. Results showed that the influence of Pr addition on catalytic performance of the CeO2(ZrO2)/TiO2 catalysts was different between the sol-gel method and the impregnation method. The Pr addition tended to interact with TiO2 and formed the structure of Ti-O-Pr in the sol-gel method while it was more likely to interact with CeO2 forming the structure of Ce-O-Pr in the impregnation method. The total acid amount and redox properties of the catalysts prepared by sol-gel method decreased with the addition of Pr element, which resulted in decrease of catalytic activity. In contrast, the Pr-added catalyst prepared by impregnation method was found to possess easier reducibility, more total acid amount and higher proportion of Ce3+ species, which was favourable for higher catalytic activity.

Influence of Ni to Co ratio supported on ZrO2 catalysts in phenol steam reforming for hydrogen production

In this work, catalytic steam reforming of phenol for hydrogen production was investigated. This study focuses on the effects of Ni to Co ratio supported on ZrO2 catalysts. The NixCoy/ZrO2 (x = 0, 1, 2, 3, 4 where x + y = 4) catalysts were prepared by impregnation method. Steam reforming activity was tested in a fixed bed reactor at 600 °C using a feed of phenol/water mixture at a molar ratio of 1:9 and a constant liquid feed rate of 0.36 ml/min. The catalysts were characterized by BET surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), NH3 Temperature-Programmed Desorption (NH3-TPD), CO2 Temperature-Programmed Desorption (CO2-TPD), H2 Temperature-Programmed Reduction (H2-TPR) and thermo-gravimetric analysis (TGA). The increase in the Co content from 0 to 4, caused a decrease in the crystal size, the t-ZrO2 phase and the reducibility of the catalysts. However, it only slightly affected the total surface area. It was found that metallic Ni4 and Co4 catalysts have lower activity towards phenol steam reforming and deposit higher coke due to having higher acidity sites compare to bimetallic catalysts. In contrast, Ni3Co1 displayed a superior catalytic activity among all the catalysts, suggesting the presence of the highest basic site and high coking resistance. Phenol conversion of 53.5% and hydrogen yield of 50.4% were achieved with the Ni3Co1 catalyst, even though its activity decreased by increasing the cobalt content.

Catalytic cracking of light diesel over Au/ZSM-5 catalyst for increasing propylene production

The catalytic cracking of light diesel oil (235–337 °C) over gold-modified ZSM-5 was investigated in a small confined fluidized bed at 460 °C and ambient pressure. Different Au/ZSM-5 catalysts were prepared by a modified deposition-precipitation method by changing the preparation procedure and the amount of gold loading and were characterized by X-ray diffraction, N2 adsorption-desorption, temperature-programmed desorption of NH3, transmission electron microscopy and inductively coupled plasma spectrometer. It was found that a small amount of gold had a positive effect on the catalytic cracking of light diesel oil and increased propylene production at a relatively low temperature. The maintenance of the ZSM-5 MFI structure, pore size distribution and the density of weak and strong acid sites of the Au/ZSM-5 catalysts depended on the preparation parameters and the Au loading. Simultaneous enhancement of the micro-activity and propylene production relies on a synergy between the pore size distribution and the relative intensity of the weak and strong acid sites. A significant improvement in the micro-activity index with an increase of 4.5 units and in the propylene selectivity with an increase of 23.2 units was obtained over the Au/ZSM-5 catalyst with an actual Au loading of 0.17 wt%.

Modification of Cu/ZSM-5 catalyst with CeO2 for selective catalytic reduction of NOx with ammonia

Cu/ZSM-5 and CeO2-modified Cu/ZSM-5 catalysts were prepared by a wetness impregnation method. The addition of CeO2 was found to enhance the NOx selective catalytic reduction (SCR) activity of the catalyst at low temperatures, but the high-temperature activity was weakened. The catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), H2 temperature-programmed reduction (TPR) and NH3 temperature-programmed desorption (TPD). The results showed that more CuO clusters instead of isolated Cu2+ species were obtained on the modified catalyst. These active CuO clusters, as well as the Cu-Ce synergistic effect, improved the redox property of the catalyst and low-temperatures SCR activity via promoting the oxidation of NO to NO2 and fast SCR reaction. The loss in high-temperatures activity was attributed to the enhanced competitive oxidation of NH3 by O2 and decreased surface acidity of the catalyst.

Reactivity of a Carbon-Supported Single-Site Molybdenum Dioxo Catalyst for Biodiesel Synthesis

A single-site molybdenum dioxo catalyst, (Oc)2Mo(═O)2@C, was prepared via direct grafting of MoO2Cl2(dme) (dme = 1,2-dimethoxyethane) on high-surface-area activated carbon. The physicochemical and chemical properties of this catalyst were fully characterized by N2 physisorption, ICP-AES/OES, PXRD, STEM, XPS, XAS, temperature-programmed reduction with H2 (TPR-H2), and temperature-programmed NH3 desorption (TPD-NH3). The single-site nature of the Mo species is corroborated by XPS and TPR-H2 data, and it exhibits the lowest reported MoOx Tmax of reduction reported to date, suggesting a highly reactive MoVI center. (Oc)2Mo(═O)2@C catalyzes the transesterification of a variety of esters and triglycerides with ethanol, exhibiting high activity at moderate temperatures (60–90 °C) and with negligible deactivation. (Oc)2Mo(═O)2@C is resistant to water and can be recycled at least three times with no loss of activity. The transesterification reaction is determined experimentally to be first order in [ethanol] and f...

Experimental and kinetic study of n-heptane isomerization on nanoporous Pt-(Re, Sn)/HZSM5-HMS catalysts

Pt-(Sn,Re)/HZSM5-HMS catalysts were evaluated for n-heptane isomerization at 200–350 °C. To characterize the catalyst, X-ray diffraction, X-ray fluorescene, Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, infrared spectroscopy of adsorbed pyridine, H2 chemisorption, nitrogen adsorption-desorption, scanning electron microscopy and thermogravimetric analysis were performed. Kinetics of n-C7 isomerization were investigated under various hydrogen and n-C7 pressures, and the effects of reaction conditions on catalytic performance were studied. The results showed that bi- and trimetallic catalysts exhibit better performance than monometallic catalysts for this reaction. For example, a maximum i-C7 selectivity (> 74%) and multibranched isomer selectivity (40%) were observed for Pt-Sn/HZSM5-HMS at 200 °C.

Promotional effects of Er incorporation in CeO2(ZrO2)/TiO2 for selective catalytic reduction of NO by NH3

A series CeO2(ZrO2)/TiO2 catalysts were modified with Er using a sol-gel method. The catalytic activity of the obtained catalysts in the selective catalytic reduction (SCR) of NO with NH3 was investigated to determine the appropriate Er dosage. The catalysts were characterized using X-ray diffraction, N2 adsorption, NH3 temperature-programmed desorption, H2 temperature-programmed reduction, photoluminescence spectroscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The results showed that the optimum Er/Ce molar ratio was 0.10; this catalyst had excellent resistance to catalyst poisoning caused by vapor and sulfur and gave more than 90% NO conversion at 220–395 °C and a gas hourly space velocity of 71 400 h−1. Er incorporation increased the Ti3+ concentrations, oxygen storage capacities, and oxygen vacancy concentrations of the catalysts, resulting in excellent catalytic performance. Er incorporation also decreased the acid strength and inhibited growth of TiO2 and CeO2 crystal particles, which increased the catalytic activity. The results show that high oxygen vacancy concentrations and oxygen storage capacities, large amounts of Ti3+, and low acid strengths give excellent SCR activity.