Al2O3 Support Research Articles

Pt/Al2O3 with ultralow Pt-loading catalyze toluene oxidation: Promotional synergistic effect of Pt nanoparticles and Al2O3 support

A kind of highly efficient and low cost supported-Pt catalyst for oxidation of toluene is obtained through controlling both the chemical state of Pt active sites and surface properties of supports. The optimized Pt/Al2O3 catalyst with Pt loading as low as 0.1 wt% could completely convert toluene (1000 ppm) to CO2 at about 180 ℃ under a space velocity of 24,000 mL g−1 h−1. It also exhibits a high stability and moisture resistance properties under reaction atmosphere. TOF value calculated with the dispersion of Pt can reach 0.0685 s-1, representing a high utilization efficiency of Pt. A series of characterizations are carried out to investigate the key factors affecting the catalytic performance of Pt/Al2O3, and disclose the concrete role of Pt and Al2O3 in the activation of molecular oxygen and toluene. In situ DRIFTS and EPR results show that Pt is the active center for O2 activation. Metallic Pt nanoparticles (Pt0) can activate the molecular O2 even at room temperature. Al2O3 offers sites for the adsorption of toluene and desorption of CO2 product. The weak and medium strength of acid-base sites favorite the adsorption and desorption process. The oxidation of toluene over Pt/Al2O3 obeys modified L-H mechanism. The synergistic effect of metallic Pt nanoparticles and suitable Al2O3 support is critical for obtaining highly efficient Pt-based catalysts with low Pt contents for toluene oxidation.

Nickel-Containing Polyoxotungstates Based on [PW9O34]9– and [PW10O39]13– Keggin Lacunary Anions Supported on Al2O3 for Dibenzothiophene Hydrodesulfurization Application

In the present study, different Al2O3-supported Ni-containing polyoxotungstates (POW) based on Keggin lacunary structures were synthesized in order to establish a correlation between the local conformation of the different Ni/POWs and the final catalytic performance of the corresponding supported NiW hydrodesulfurization (HDS) catalysts. POWs containing various amounts of nickel (3, 4, or 9 Ni atoms per POW) were therefore prepared and supported on an Al2O3 support obtained by a sol–gel method using impregnation techniques in aqueous solutions at two different pH values (7 and 9). The as-obtained supported Ni-containing POWs were characterized after the drying (120 °C, 4 h) and calcination steps (400 °C, 4 h, air). The different solids were then sulfided using 10 mol % H2S in H2 at 400 °C for 4 h and evaluated in the hydrodesulfurization of dibenzothiophene (DBT) at T = 300 °C and P = 30 bar H2. Both the Ni localization inside the polyoxotungstate and the pH of the impregnation solution influence the degr...

Catalytic Activity of Nickel and Ruthenium–Nickel Catalysts Supported on SiO2, ZrO2, Al2O3, and MgAl2O4 in a Dry Reforming Process

Dry reforming of methane (DRM) is an eco-friendly method of syngas production due to the utilization of two main greenhouse gases—methane and carbon dioxide. An industrial application of methane dry reforming requires the use of a catalyst with high activity, stability over a long time, and the ability to catalyze a reaction, leading to the needed a hydrogen/carbon monoxide ratio. Thus, the aim of the study was to investigate the effect of support and noble metal particles on catalytic activity, stability, and selectivity in the dry reforming process. Ni and Ni–Ru based catalysts were prepared via impregnation and precipitation methods on SiO2, ZrO2, Al2O3, and MgAl2O4 supports. The obtained catalysts were characterized using X-ray diffractometry (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer–Emmett–Teller (BET) specific surface area, and elemental carbon-hydrogen-nitrogen-sulphur analysis (CHNS) techniques. The catalytic activity was investigated in the carbon dioxide reforming of a methane process at 800 °C. Catalysts supported on commercial Al2O3 and spinel MgAl2O4 exhibited the highest activity and stability under DRM conditions. The obtained results clearly indicate that differences in catalytic activity result from the dispersion, size of an active metal (AM), and interactions of the AM with the support. It was also found that the addition of ruthenium particles enhanced the methane conversion and shifted the H2/CO ratio to lower values.

Alkene Hydrosilylation on Oxide‐Supported Pt‐Ligand Single‐Site Catalysts

AbstractHeterogeneous single‐site catalysts (SSCs), widely regarded as promising next‐generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt‐ligand SSCs through a novel metal‐ligand self‐assembly method on MgO, CeO2, and Al2O3 supports (J. Catal. 2018, 365, 303–312). Here, we present their applications in the industrially‐relevant alkene hydrosilylation reaction, with 95 % yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the single‐site structure remains intact on oxide supports after reaction. Pt single‐sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal‐ligand self‐assembly strategy in an industrially‐relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts.

The effect of Al3+ coordination structure on the propane dehydrogenation activity of Pt/Ga/Al2O3 catalysts

Abstract The effect of the Al2O3 structure on the performance of Pt/Ga/Al2O3 catalysts is investigated for the direct dehydrogenation of propane. The study unveils that the structure of Al3+ determines the bulk structure of catalysts, particularly a high content of coordinatively unsaturated Al3+ sites (penta-coordinated Al3+, denoted as Al3+penta) could lead to a remarkably improved dehydrogenation activity of the catalyst. The bulk characterization reveals that the sufficient amount of Al3+penta in Al2O3 benefit the dispersion of Pt and Ga2O3 on the Al2O3 support. At the same time, TPR results reveal that the presence of Pt facilitates the reduction of Ga2O3, likely due to the hydrogen spillover between the well dispersed Pt and Ga2O3, which consequently enhances the synergistic function between Pt and Ga2O3 in the dehydrogenation of propane. Recyclability tests demonstrate that the dehydrogenation activity stabilizes after three cycles over the Pt/Ga/Al2O3 catalyst.

Fundamentals of Sulfate Species in Methane Combustion Catalyst Operation and Regeneration—A Simulated Exhaust Gas Study

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al2(SO4)3 over Al2O3 support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdOx. The presence of Al2(SO4)3 increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated.

Effect of CeO2 loading of the Ce-Al mixed oxide on ultrahigh temperature water-gas shift performance over Ce-Al mixed oxide supported Ni catalysts

The purpose of this study is to investigate and to evaluate the effect of CeO2 loading in the Ce-Al mixed oxide (CeO2-Al2O3) on physicochemical properties as well as the ultrahigh temperature water-gas shift (UHT-WGS) catalytic performance of Ni/x wt.%CeO2-Al2O3 (xCe-Al; x = 1, 3, 5, 7, and 10) catalysts. The Al2O3 (Al) and the xCe-Al supports were synthesized via the sol-gel method. The Ni/Al and Ni/xCe-Al catalysts were prepared by the incipient wetness impregnation method. The catalysts were characterized using XRD, the N2 adsorption-desorption isotherms, H2-TPD, H2-TPR, TEM and TGA/DTA. The UHT-WGS catalytic performance of these catalysts were carried out in a packed-bed tubular reactor. The results reveal that adding CeO2 to the Al2O3 support for the Ni supported catalyst increased the surface area resulting in the enhancement of nickel dispersion and reducibility of the Ni/xCe-Al catalysts. However, under certain circumstances, bulk CeO2 can separate from the support to the catalyst surface and partially cover the Ni metal in the case of high CeO2 loading. Compared to other catalysts, the Ni/5Ce-Al catalyst illustrates the highest UHT-WGS catalytic activity (CO conversion >75%) with the maintainability. This proposed composition provides the appropriate Ni-Ce-Al interaction that also suppresses the graphitic/filamentous carbon.

Characterization of Highly Active Al2O3-TiO2 Supported Pt and Pd Catalysts for Hydrodechlorination of 1,2-Dichloroethane

Abstract Al2O3-TiO2 (AT) mixed oxide with atomic ratio Al/Ti = 25 and Al2O3 (A) supports were prepared by the sol-gel method and impregnated to obtain monometallic Pd and Pt (1 wt % of metal), and bimetallic PdPt (Pd/Pt = 4) catalysts. These catalysts were tested in the gas-phase hydrodechlorination of 1,2 dichloroethane. The materials were characterized by nitrogen physisorption, X-ray diffraction analysis (XRD), temperature-programmed reduction (TPR) and high-resolution transmission microscopy (HRTEM). AT support showed a BET area (422 m2/g), slightly higher than A(374 m2/g). The specific activity for the AT supported catalysts was higher than that for the A supported catalysts. The order of activity for the AT supported catalysts was as follows: Pd> PdPt> Pt and in terms of selectivity towards non-chlorinated compounds the order was PdPt> Pd> Pt. The differences in the activities and the selectivities can be explained by the presence of different species of Pd in the supported catalysts.

Reductive amination of polypropylene glycol using Ni-CeO2@Al2O3 with high activity, selectivity and stability

Ni-only and Ni-CeO2 particles decorated on Al2O3 support material were prepared for an effective catalytic reductive amination of polypropylene glycol (PPG) to polyetheramines (PEA). Incipient wetness impregnation was employed for the preparation of catalysts followed by complementary material characterization (powder XRD, SEM, HRTEM, XPS, H2-TPR and NH3-TPD). High selectivity to PEA (~ 100%) was achieved. The catalytic activity obtained was proportional to Ni and Ce loadings (CCe), when CCe ≤ 15%. Hybridization with CeO2 inhibited formation of nickel nitride and enhanced activity (by 15.3%) and operation stability of Ni catalyst (by 20×). The present work has demonstrated a facile route to fabricate Ni-CeO2 hybrid catalysts on alumina support material and provided mechanistic understanding of the synergistic effect occurred for the heterogeneous catalytic reductive amination.

Effect of surface acidity of Al2O3 supported metal catalysts on catalytic activity and carbon deposition during SCWG of glucose

In this study, the impact of a catalyst's surface acidity on supercritical water gasification (SCWG) of glucose is investigated. Four different catalysts including Ni, Ru0·2Ni, Ru0·5Ni and NiLa were prepared on an Al2O3 support via an incipient impregnation method. NH3-TPD and pyridine-FTIR results of the fresh catalysts showed that NiLa was the least acidic amongst the four investigated catalysts. Although the BET surface area for all four catalysts were similar, the NiLa and Ru0·5Ni catalysts were found to significantly reduce carbon deposition during SCWG of glucose, attributed to their lower acidic nature. Production of H2 was also increased by 1.52 and 1.21 × using the NiLa and Ru0·5Ni compared to Ni. The carbon deposition was characterized by TG-DTA, TPO, XRD and Raman spectroscopy, showing that the higher the acidic nature of the catalyst, the higher the tendency for carbon deposition. Using a lower acidic catalyst for SCWG helped minimize the catalyst's deactivation, while improving the catalyst lifetime This study shows that the acidic nature of the catalyst is an important consideration towards a better understanding of the SCWG mechanism.

Enhanced Conversion in the Direct Synthesis of Diethyl Carbonate from Ethanol and CO2 by Process Intensification

AbstractTo overcome the low equilibrium conversion in the direct synthesis of diethyl carbonate from ethanol and CO2 under moderate reaction conditions, the reaction was conducted in a membrane reactor packed with pelletized Cu‐Ni:3‐1 supported on activated carbon. A SiO2/γ‐Al2O3 commercial membrane and zeolite A membranes synthesized on commercial Al2O3 supports were evaluated in the membrane reactor. Although characterization of the membranes by X‐ray diffraction confirmed the presence of a zeolite A layer on the supports, gas permeation and permselectivity tests of ethanol and water evidenced some defects of the synthesized membranes. An increase in conversion with respect to a conventional packed‐bed reactor was observed in the membrane reactors prepared on Al2O3, but equilibrium conversion was not attained. However, with the commercial membrane, the ethanol conversion was higher than the equilibrium conversion.

One‐step Conversion of Fructose to Furfuryl Alcohol in a Continuous Fixed‐bed Reactor: The Important Role of Supports

AbstractOne‐step catalytic conversion of fructose to furfuryl alcohol (FOL) is not only a challenge task but also to open a new pathway for conversion of hexose into useful chemicals. The favorable yield (41.6 %) of FOL can be directly obtained from fructose over the tandem of HY zeolite and Pd/Al2O3. However, the Pd/montmorillonite (Pd/MMT) was deactivated for production of FOL. The proportion of available Pd active sites (i. e. facets, corners and edges) vary with different supports, and the strong metal support interaction (SMSI) plays the pivotal role on the catalytic performance. For Al2O3 support, exposure of Pd (111) plane allows the hydroxymethylfurfural (HMF) to bind on the Pd (111) surface via planar arrangement. In this stance, the aldehyde group of HMF is readily eliminated by decarbonylation. Conversely, for Pd/MMT, the decarbonylation is completely inhibited due to the HMF absorbs on corner sites in perpendicular orientation. The XPS studies indicate that the density electron of Pd nanoparticles (NPs) could be manipulated by various supports, and the electron‐donating effect of Al2O3 was observed. The collaborative effects between available sites and density electron of Pd are observed with respect to the different binding modes of HMF on the surface of Pd. The electronegative Pd NPs facilitate the decarbonylation of HMF as a consequence of the different adsorption strength between furan ring and aldehyde group.

Photocatalytic and Pozzolanic Properties of Nano-SiO₂/Al₂O₃-TiO₂ Powder for Functional Mortar.

The present study intended to find a way to use TiO2, one of the most widely used photocatalysts, as a construction material. To that end, nano-SiO2/Al2O3-TiO2 powder (NTCP) was synthesized by coating SiO2 and Al2O3 support materials with TiO2. The NTCP was anatase phase spherical particles, specific surface areas were 319 m2/g and 267 m2/g for the SiO2-TiO2 powder and Al2O3-TiO2 powder. UV absorption test results showed the developed NTCP had a light absorption peak at wavelengths of 380 nm or below, and its absorbance was much larger than that of commercial TiO2. The NTCP formed smaller pores on the surface than commercial TiO2. As a result, the flow of the mortar decreased as the adsorption strength increased and combined a large number of water molecules. In addition, the Pozzolanic reaction by SiO2 and Al2O3 used as support materials produced many calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). This has shown an increased strength of mortar mixed with the NTCP by promoting a nucleation effect and reducing the filling effect and the number of harmful holes in the mortar.

Phosphonic acid modifiers for enhancing selective hydrodeoxygenation over Pt catalysts: The role of the catalyst support

Bifunctional catalysts comprised of both noble metal and Brønsted acid sites are of growing interest for many reactions, such as the hydrodeoxygenation (HDO) of oxygenates produced by the deconstruction of lignocellulosic biomass. One method of preparing a bifunctional metal-acid catalyst is to modify the supporting material of a metal catalyst with acid-containing ligands, such as phosphonic acids (PAs), which provide tunable Brønsted acid sites at the metal-support interface. Here, we explore the potential for PA modification to improve HDO rates on Al2O3, TiO2, CeO2, and SiO2-Al2O3 supports. PAs containing either alkyl or carboxylic acid (CA) tails were used to modify Pt catalysts on each support. PA modification improved HDO rates for the model compound benzyl alcohol when applied to Pt supported by Al2O3, TiO2, and CeO2, but had a negative effect on the HDO rate of Pt/SiO2-Al2O3. Measurements of the relative strength of Brønsted acid sites present on the modified and unmodified catalysts suggested that PAs improved HDO when they provided new or stronger Brønsted acid sites. Additionally, the strength of the Brønsted acid sites provided by PA modifiers were tunable by altering the tail functionality, which affected the rates of HDO. These results suggest that PAs can be used to modify a variety of supports to prepare bifunctional acid-metal catalysts.

Photocatalytic Activity of Ga2O3 Supported on Al2O3 for Water Splitting and CO2 Reduction.

We have examined the photocatalytic activity of Ga2O3 supported on Al2O3 (Ga2O3/Al2O3 catalyst) without a noble metal cocatalyst for water splitting and reduction of CO2 with water under UV light irradiation by changing the loading amount of Ga2O3. All prepared Ga2O3/Al2O3 catalysts show photocatalytic activities for both water splitting and CO2 reduction, and their activities are significantly improved compared to those of nonsupported Ga2O3 and Al2O3. The water splitting is dominated for Ga2O3/Al2O3 with less than 1.0 vol % of Ga2O3 loaded, whereas the CO2 reduction, for higher Ga2O3-loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga2O3/Al2O3 catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga2O3 rods dispersed on an Al2O3 support consisting of a little distorted α-Ga2O3 phase. On the other hand, the CO2 reduction proceeds on sub-micrometer-sized Ga2O3 particles consisting of mixed phases of α-Ga2O3 and γ-Ga2O3 or with appearance of boundaries between the α and γ phases, which plays a critical role. Al2O3 used as the support of the Ga2O3 particles does not seem to play an important role in the photocatalytic CO2 reduction.

The effect of Si/Al ratio of zeolite supported Pd for complete CH4 oxidation in the presence of water vapor and SO2

The catalytic properties of palladium supported on H-beta and H-SSZ-13 zeolite with different silica to alumina ratio (SAR) have been evaluated for complete CH4 oxidation in the presence and absence of water vapor and together with SO2. Different SAR was successfully obtained by dealumination of the zeolites in an acidic solution at elevated temperature. Flow reactor experiments showed that the SAR of the zeolite support greatly impacts the catalytic activity, especially in the presence of water vapor. Pd supported on a highly siliceous beta zeolite expressed high and stable CH4 conversion in the presence of water vapor, whereas the activity for Pd supported on zeolites with low SAR or Al2O3 decreased over time due to accumulative water deactivation. Hence, an increased SAR of the zeolite support clearly correlates to a lower degree of water deactivation. We suggest that this is a result of the high hydrophobicity of the siliceous zeolites. The results also imply that the catalytic activity in the presence of water vapor is influenced more by the SAR than the type of the zeolite framework. The CH4 oxidation activity was also enhanced with increasing SAR under dry conditions. This was addressed to the formation of more Pd particles in relation to ion-exchanged Pd2+ species and changes of the oxidation-reduction behavior of the Pd. The high number of acidic sites in zeolites with low SAR provided higher dispersion of Pd particles and formation of more monoatomic Pd2+ species, whereas almost exclusively Pd particles of larger sizes were formed on the highly siliceous zeolites. The monoatomic Pd2+ species, mostly formed on zeolites with low SAR, were oxidized and reduced at significantly higher temperatures than Pd in the particle form. Hence, complete reduction or oxidation of the Pd supported on highly siliceous zeolites can be achieved at lower temperatures. Moreover, compared to Pd/Al2O3, the zeolite supported Pd expressed higher sensitivity to SO2. However, the major part of the catalytic activity could be regenerated more easily using siliceous zeolites as supports compared to Al2O3. We suggest that this is an effect of the lower SO2 adsorption on the zeolite supports than on the Al2O3 support, which results in the formation of more PdSOx species upon SO2 exposure. On the other hand, the low SO2 adsorption on the zeolites also results in less spillover of sulfur species from the support to the active PdO, which explains the facilitated regeneration.

Silver sulfate catalyst for soot oxidation with high resistance to sulfur poisoning

This study investigates the soot oxidation activity and mechanism of an Al2O3-supported Ag2SO4 catalyst with novel active species. The Ag2SO4/Al2O3 catalyst exhibits higher soot oxidation activity under loose contact conditions compared to Ag/Al2O3 and Ag/CeO2 catalysts. Moreover, it is hardly affected by sulfur poisoning and maintains its high activity after sulfur poisoning treatment. High-temperature X-ray diffraction measurements suggest that a part of Ag2SO4 on the Al2O3 support melts and creates contact between the Ag2SO4 and soot at temperatures over 400 °C, resulting in higher soot oxidation activity even under loose contact conditions. The soot oxidation mechanism over the Ag2SO4/Al2O3 catalyst is probed by oxygen isotope exchange analysis and operando X-ray absorption fine structure measurements, which reveal that the oxygen chemically bound in Ag2SO4 is utilized for soot oxidation. In particular, the above oxidation features a reversible redox cycle comprising partial reduction of Ag2SO4 to metallic Ag that is further re-oxidized to Ag2SO4 by the gas-phase oxygen.

Effect of acidity of oxide support on the activity and stability of μ-nitrido diiron phthalocyanine complex

Various oxides, including Al2O3, Fe2O3, SiO2, and ZrO2, were employed as catalyst supports for the oxidation of cyclohexane by a μ-nitrido-bis[tetra(tert-butyl)phthalocyaninatoiron] complex. These oxide supports were characterized by Brunauer–Emmett–Teller surface area measurements and NH3 temperature-programmed desorption analyses. The catalyst supported on Al2O3, which has the highest acidity among the oxides considered here, showed the best activity with a turnover number (TON) of ˜108.8, without any co-catalyst. Furthermore, recycle tests of the catalysts revealed a TON of 69.3 for the Al2O3-supported catalyst after the third run. The strongly acidic sites in the Al2O3 support could be responsible for the strong adsorption of μ-nitrido diiron phthalocyanine, resulting in enhanced catalytic activity and stability.

Long-Term Stability of Thin-Film Pd-Based Supported Membranes

Membrane reactors have demonstrated a large potential for the production of hydrogen via reforming of different feedstocks in comparison with other reactor types. However, the long-term performance and stability of the applied membranes are extremely important for the possible industrial exploitation of these reactors. This study investigates the long-term stability of thin-film Pd-Ag membranes supported on porous Al2O3 supports. The stability of five similarly prepared membranes have been investigated for 2650 h, up to 600 °C and in fluidized bed conditions. Results show the importance and the contribution of the sealing of the membranes at temperatures up to 500 °C. At higher temperatures the membranes surface deformation results in pinhole formation and a consequent decrease in selectivity. Stable operation of the membranes in a fluidized bed is observed up to 450 °C, however, at higher temperatures the scouring action of the particles under fluidization causes significant deformation of the palladium surface resulting in a decreased selectivity.

Highly selective production of C5-C12 hydrocarbons over efficient Ru/heteropoly-acid catalysts

It is a great challenge in catalysis to increase selectivity without sacrificing activity. Furthermore, the highly selective production of C5-C12 hydrocarbons, which are main components of gasoline fuel, from syngas is important for Fischer-Tropsch synthesis (FTS), particularly for its industrial process. Herein, we demonstrate an approach to increase selectivity for C5-C12 hydrocarbons, namely, the 145% increase in selectivity of C5-C12 hydrocarbons without sacrificing high CO conversion was obtained by tuning Al2O3 support with tungstophosphoric acid (HPW) for Ru-based catalysts. This finding offers a simple and novel approach to develop efficient catalysts for FTS.