Amorphous Silica-alumina Catalysts Research Articles

Effect of acidity of solid acid catalysts during non-oxidative thermal decomposition of LDPE

AbstractThermal decomposition of low-density polyethylene (LDPE) was monitored by thermogravimetry under N2 atmosphere in the presence of solid acid catalysts such as alumina (α-Al2O3, γ-Al2O3), crystalline silica-alumina (SA, molar ratio of Si/Al = 0.19) and amorphous silica-alumina catalysts (ASA, molar ratio of Si/Al = 4.9). Crystal structure and surface area of solid acid catalysts were measured by XRD and BET, respectively. The strength and distribution of acid sites of solid acid catalysts were estimated by NH3-TPD. It was observed that total acidity strength is in the order of ASA (1.77 μmmol NH3/g) > AS (1.42 μmol NH3/g) > γ-Al2O3 (1.06 μmol NH3/g) > α-Al2O3 (0.06 μmol NH3/g). Thermal degradation behavior of LDPE with and without solid acid catalyst was monitored by TGA, where heating rates (β) of 5, 10, and 20 °C/min were employed under an inert atmosphere, and their activation energies (Ea), onset temperatures (Tinitial), decomposition temperatures (Tdecomp) were calculated and compared. The activation energy (Ea) was evaluated using the Coats-Redfern method. Solid acid catalysts with stronger acidity and higher surface area showed a decrease in activation energy and onset temperature. Activation energy of LDPE over ASA catalyst is decreased to 97.3 kJ/mol from thermal decomposition of LDPE without catalyst of 117.2 kJ/mol under heating rate of 10 °C/min. The isothermal decomposition of LDPE was monitored at 300 °C for 3 h with a heating rate of 10 °C/min, where 13.1% and 24.2% wt. loss were observed over SA and ASA, respectively, while only 0.7% wt. loss was observed for LDPE without a solid acid catalyst. Graphical abstract Single step decomposition of LDPE Thermal degradation behavior of LDPE monitored by TGA, with different heating rates (β) of 5, 10, 20 °C/min.

Highly stable amorphous silica-alumina catalysts for continuous bio-derived mesitylene production under solvent-free conditions

Amorphous silica-alumina are efficient and highly stable catalysts for the continuous production of biomass-derived aromatics such as mesitylene from acetone, thus adding to the potential for value creation in biorefineries.

Transition metal chalcogenide bifunctional catalysts for chemical recycling by plastic hydrocracking: a single-source precursor approach.

Sulfided nickel, an established hydrocracking and hydrotreating catalyst for hydrocarbon refining, was synthesized on porous aluminosilicate supports for the hydrocracking of mixed polyolefin waste. Zeolite beta, zeolite 13X, MCM41 and an amorphous silica-alumina catalyst support were impregnated with the single-source precursor (SSP) nickel (II) ethylxanthate for catalyst support screening. Application of this synthesis method to beta-supported nickel (Ni@Beta), as an alternative to wet impregnation using aqueous nickel (II) nitrate, provided catalytic materials with higher conversion to fluid products at the same mild batch reaction conditions of 330°C with appropriate agitation and 20 bar H2 pressure. Mass balance quantification demonstrated that SSP-derived 5wt%Ni@Beta yielded a greater than 95 wt% conversion of a mixed polyolefin feed to fluid products, compared with 39.8 wt% conversion in the case of 5wt%Ni@Beta prepared by wet impregnation. Liquid and gas products were quantitatively analysed by gas chromatography–flame ionization detection (GC-FID) and gas chromatography–mass spectrometry (GC-MS), revealing a strong selectivity to saturated C4 (37.3 wt%), C5 (21.6 wt%) and C6 (12.8 wt%) hydrocarbons in the case of the SSP-derived catalyst.

Causes of deactivation of an amorphous silica-alumina catalyst used for processing of thermally cracked naphtha in a bitumen partial upgrading process

Thermally cracked naphtha represents a challenging feed for many catalytic processes. Its contaminant content and reactivity cause the deactivation of catalysts. Nevertheless, the use of an amorphous silica-alumina acid catalyst to convert and reduce the alkene content in thermally cracked naphtha was possible. The purpose of this study was to determine the cause(s) of catalyst deactivation by analysis of spent catalysts after conversion of cracked naphtha at different conditions in the range 250–350 °C, 6 MPa and WHSV of 0.5–2 h−1. It was found that nitrogen bases, suspected to be important acid catalyst poisons, were not the main cause of catalyst deactivation. Nitrogen was more abundant in deposits on the catalyst at the inlet compared to the outlet of the reactor, but the accumulated nitrogen in deposits represented only a minor fraction of the total amount of basic nitrogen to which the catalyst was exposed. Carbonaceous deposits were the main cause of catalyst deactivation and the profile of the deposition on the catalyst changed with temperature. At 325 °C the amount of deposits at the reactor outlet was higher, with lower H/C ratio and higher persistent free radical content than at the reactor inlet. Although some of the precursor species that formed deposits were present in the feed, some of the precursor species that formed deposits were produced during the conversion process. Although the contribution of acid catalysis was not ruled out, many observations in the study indicated that carbonaceous deposits formed mainly due to free radical reactions.

Rates of levoglucosanol hydrogenolysis over Brønsted and Lewis acid sites on platinum silica-alumina catalysts synthesized by atomic layer deposition

Nanoscale coatings of AlOx were deposited onto SiO2 using atomic layer deposition (ALD) to synthesize amorphous silica-alumina (SiAl) catalysts, and these catalysts were investigated for levoglucosanol (Lgol) hydrogenolysis. With decreasing Al2O3 loading, the ratio of Brønsted to Lewis acid sites, measured by NH3-TPD and pyridine-FTIR, systematically increases, while the Al coordination, measured by solid state 27Al NMR, decreases. These structural changes correspond to an increasing mass-normalized rate of Lgol hydrogenolysis. We model the mass-normalized reaction rate as the sum of independent contributions from Brønsted and Lewis sites, showing that Brønsted acid sites on ALD-AlOx/SiO2 catalysts have a 6-times higher turnover frequency (TOF) than Lewis acid sites on these catalysts. Additionally, Lewis acid sites on ALD-AlOx/SiO2 catalysts (potentially related to Al(V) species) have a 4-times higher TOF than Lewis acid sites on bulk γ-Al2O3. The overall mass-normalized reactivity of ALD-AlOx/SiO2 catalysts is due to Lewis acid sites at the highest Al2O3 loading, while it is predominantly due to Brønsted acid sites at the lowest Al2O3 loadings. This work provides a new approach to synthesize amorphous SiAls with tunable Brønsted/Lewis acid site ratio and reveals differences in the reactivity of Brønsted and Lewis acid sites on these materials.

Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites.

In spite of the widespread applications of amorphous silica-aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si-29Si, 27Al-27Al, and 29Si-27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's rule of aluminum avoidance. 3D 17O{1H} and 2D 17O{1H,27Al} experiments were developed to measure site-specific O-H and HO-Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

Bio-gasoline Production by Coupling of Biomass Catalytic Pyrolysis and Oligomerization Process

Abstract Biomass catalytic cracking produced aromatics and olefins-rich fuel gas. In this paper, the C 5 -C 12 iso-olefins and iso-alkanes were produced by oligomerization of olefins-rich fuel gas. The amorphous silica-alumina (ASA) was used as catalyst for olefins oligomerization reaction. The conversion of ethylene, propylene and butylene reached 19.2%, 37.3% and 58.7%, respectively. The yield of C 5 -C 12 products reached 23.43c-mol%. The bio-gasoline was the mixture of the produced aromatics and C 5 -C 12 iso-alkanes. Results showed that 1Kg rice straw biomass could produce 0.226Kg bio-gasoline. The thermal efficiency from biomass to bio-gasoline reached 49.5%. Coke formation on the ASA catalyst resulted in the activity lost. After generation by combustion of the deposited coke, the properties of spent ASA catalyst was recovered. Coupling of biomass catalytic pyrolysis and olefins oligomerization to bio-gasoline is an excellent approach with high efficiency.

Advanced kinetic models through mechanistic understanding: Population balances for methylenedianiline synthesis

The recent development of amorphous silica-alumina catalysts for the heterogeneously-catalyzed production of methylenedianiline (MDA) has resulted in an economically and environmentally attractive alternative to the industrially employed HCl catalyst. However, the quantitative kinetic description of the complex reaction network, a key prerequisite for reactor choice and process assessment, is unfeasible when using classical power-law based models due to the wealth of components and interactions involved. Based on high throughput batch experiments coupled with a detailed product analysis, we herein reveal that all possible reactions in an MDA mixture can be represented in terms of interactions between a small number of reoccurring functional groups. A corresponding categorization of all mixture components enables the description of the reaction network using population balance equations, an approach previously applied to polymerization, aggregation, and cell-growth processes. Thereby, every possible binary interaction between two molecules in the system can be accounted for, resulting in an unprecedented resolution regarding oligomeric species and improved predictive capabilities based on a small number of parameters. The translation of the deepened mechanistic understanding into advanced kinetic models enables to circumvent previous limitations, and is expected to accelerate the industrial realization of the sustainable process.

Synthesis-property-performance relationships of amorphous silica-alumina catalysts for the production of methylenedianiline and higher homologues

Although amorphous silica-alumina catalysts (ASA) are a promising candidate for the replacement of HCl in the production of methylenedianiline (MDA) and higher homologues, their industrial implementation has been hampered by the lack of systematic studies targeting their design. The complexity of both, the materials as well as the reaction, necessitates the development of synthesis-structure-performance relationships to indicate if, and how, the stringent specifications in terms of activity, selectivity, and stability can be met. Herein, we investigate a large set of ASA obtained by coprecipitation, deposition-precipitation, grafting, and from commercial sources. A detailed analysis of their porosity, composition, Al speciation, acidity, and morphology reveals that every synthesis method leads to a unique combination of material properties. Through high-throughput batch experiments we investigate the importance of each of these parameters for the catalytic performance. The properties that determine the activity relate to the specific surface area, which should be as large as possible while featuring tetrahedrally-coordinated aluminum atoms in the silica matrix. In contrast, the selectivity is determined by the employed reaction conditions, namely the reaction temperature and the aniline content of the feed. Continuous tests under industrial conditions reveal that ASA deactivate via fouling during the initial restructuring of aminal. Pore-mouth blockage by fouling was minimized and optimal lifetimes ensured by employing mesopore networks consisting primarily of pyramidal or cylindrical pores. Based on these insights, we demonstrate that ASA can outperform hierarchical zeolites in terms of activity, while approaching industrially attractive oligomer contents and keeping the concentration of byproducts low at a high catalyst lifetime, advertising their potential for large-scale implementation.

Chemical routes to hydrocarbons from pyrolysis of lignocellulose using Cs promoted amorphous silica alumina catalyst

Lignocellulos biomass can be converted to bio-oil containing aliphatic hydrocarbons via catalytic pyrolysis at 500°C in the presence of Cs modified amorphous silica alumina (Cs/ASA). The reaction routes for the formation of aliphatic hydrocarbons was studied using biomass constituent, viz. cellulose, hemicellulose, lignin, and single model components in a pyrolyzer system in conjunction with GC/MS. The pyrolysis behaviour of each biomass constituent was also studied using TGA. The results showed that in the presence of Cs/ASA catalyst aliphatic hydrocarbons can be formed from all the three constituents but mainly from lignin (35% of total peak area compared to 10% for cellulose) resulting in high quality bio-oil with 40Mjkg−1 heating value. On the other hand, the pyrolysis of single model compounds did not result in the aliphatic hydrocarbons. However, pyrolysis of mixture of the model compounds yielded in aliphatic hydrocarbons indicating effect of intermolecular interactions such as hydrogen transfer over Cs+ ions.

Aliphatic Hydrocarbons from Lignocellulose by Pyrolysis over Cesium‐Modified Amorphous Silica Alumina Catalysts

AbstractCesium‐modified amorphous silica alumina (Cs/ASA) is a promising catalyst for the production of hydrocarbons through pyrolysis of biomass. Catalytic pyrolysis of pinewood over Cs/ASA in a pyrolyzer system in conjunction with a gas chromatograph and mass spectrometer resulted in a 22 % yield of hydrocarbons containing more than 50 % aliphatic hydrocarbons. Factors such as the nature of the support and the concentration of Cs+ ions influenced the catalyst activity for the production of hydrocarbons. Physicochemical characterization showed that the cesium exists in the form of Cs2CO3, which interacts strongly with the ASA support.

Low temperature hydrogenation of aromatics over Pt–Pd/SiO2–Al2O3 catalyst

Bimetallic Pt–Pd catalysts supported on amorphous silica–alumina (ASA), having different amounts of SiO2 (1.5, 5, 20, 40, and 70%), are prepared by conventional impregnation method. The prepared catalysts are characterized using nitrogen adsorption–desorption isotherms at 77K and X-ray diffraction (XRD) technique, respectively. Temperature Programmed Desorption (TPD) of ammonia and CO chemisorption experiments are used to study the role of support composition on catalyst acidity and surface active noble metal content, respectively. The effect of noble metal loading and support properties on hydrogenation reaction is investigated via toluene hydrogenation reaction under varying operating conditions (temperature=383–523K, pressure=20bar, weight hourly space velocity (WHSV)=1–12h−1). Based on the obtained results, Pt (0.18wt.%)–Pd (0.18wt.%) loaded ASA catalyst with 40wt.% silica showed excellent toluene hydrogenation activity. Such trend is further reinforced from naphthalene hydrogenation studies wherein complete conversion with about 90% selectivity for decalin is noticed at 453K. Accordingly, possible advantage w.r.t. minimal noble metal loading to employ Pt (0.18wt.%)–Pd (0.18wt.%)/ASA (40% silica) catalyst for hydrogenation aromatics in transportation fuels, and producing specialty solvents such as DAK (De-aromatized Kerosene) has been envisaged.

Shape-selective alkylation of biphenyl with propylene using zeolite and amorphous silica–alumina catalysts

The influence of zeolite structure for the alkylation of biphenyl with propylene was studied over various zeolites such as HY, HZSM-5, and dealuminated mordenite (DMOR), as well as amorphous SiO2/Al2O3, in a stirred tank reactor. Biphenyl conversion was found to increase with reaction time for HZSM-5 and DMOR zeolites and reach a leveling off in 4h, whereas for HY and amorphous SiO2/Al2O3 a leveling off was reached within an hour. DMOR displayed the highest selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) even at temperatures as high as 300°C, whereas for HY, HZSM-5 and amorphous SiO2/Al2O3 selectivities fell in the range of 10–35%; they were significantly lower than observed for DMOR. These differences in selectivity might be due to the structure and pore channels of the zeolites. DMOR was found to be an active catalyst, the selectivity for 4-isopropylbiphenyl (4-IPB) and (4,4′-DIPB) was high among isopropylbiphenyl (IPB) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating DMOR possesses shape-selectivity. The selectivity of 4,4′-DIPB increased with time, while the corresponding selectivity of 4-IPB decreased for DMOR catalyst. Alkylation of biphenyl with propylene occurred with predominant formation of 4-IPB in the first step. 4-IPB is only a source in the second step of alkylation of biphenyl with propylene for the formation of 4,4′-DIPB, while 3-IPB does not participate in the formation of DIPB isomers.

Hydrocracking and Hydroisomerization of n-Hexadecane, n-Octacosane and Fischer–Tropsch Wax Over a Pt/SiO2–Al2O3 Catalyst

The hydroisomerization and hydrocracking of long chain n-paraffins and a Fischer–Tropsch wax produced with a cobalt catalyst were accomplished over a Pt–amorphous silica–alumina catalyst. The relative conversion of the n-hexadecane and n-octacosane mixed feed greatly favored the higher carbon number compound even though the conversions of the pure hydrocarbons were the same within a factor of two or less when converted separately. Thus, vapor equilibrium plays a role for the conversion of the heavier alkanes and in this case the conversion essentially occurs with only the compound present in the liquid phase. The single branched cracked products show a peak at the mid-carbon number, C8 and C14 for the two reactants, but the peak for the multi-branched product occurs at a higher carbon number. Thus, it appears that the multi-branched products are primarily produced in a series reaction with the singly branched compounds being formed as the primary products. The data for wax conversion are consistent with the competitive conversion operating for the higher carbon number compounds; however, the transport of intermediate carbon number products from the reactor occurs more rapidly than their formation rates by cracking reactions. The data clearly show that the hydrocracking of wax is dominated by vapor–liquid equilibrium and that hydrocracking is initially controlled by the compounds present in the liquid phase. Figure shows the catalyst pore filling with low boiling (left) and high boiling (right) hydrocarbons. Each reactant saturates the catalytic sites and the breaking of C–C bond occurs. Once the products from cracking of the liquid phase go into the vapor phase, it should rapidly pass the catalyst bed. This short contact time on gas phase hydrocarbons relative to the liquid phase, limits the conversion of low boiling point hydrocarbons.

PEGを用いて調製した新規非晶質シリカ-アルミナによる接触分解反応―粒子径およびPEG分子量の影響―

PEGを用いて調製した新規非晶質シリカ-アルミナによる接触分解反応―粒子径およびPEG分子量の影響―

Mono and Bifunctional Catalysts for Styrene Oxide Isomerization or Hydrogenation

Styrene oxide can be effectively isomerized to phenyl-acetaldehyde (98%) over amorphous silica alumina catalysts under very mild liquid phase conditions. On the other hand, a copper catalyst prepared using a silica zirconia support gave up to 80% yield in the hydrogenation of styrene oxide to 2-phenyl-ethanol.

Hydroisomerization of n-decane over Ni–Pt–W supported on amorphous silica–alumina catalysts

A series of NiPtW/silica–alumina catalysts (wt.%: Ni, 12–17; W: 10, Pt: 0.1–1) were prepared via a hybrid method: sol–gel and incipient wetness impregnation and characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), BET, temperature-programmed desorption of ammonia (NH 3-TPD), pyridine adsorption followed by FTIR and TPO techniques. On these catalysts, n-decane hydroisomerization was carried out under the following conditions: fixed bed reactor, atmospheric pressure, temperature ranging from 150 to 300 °C, weight hourly space velocity of 4 h −1 and molar hydrogen/hydrocarbon ratio of 5. Pt was found to promote activity and stability, the effect being optimal for 0.2 wt.% Pt. Isomers and cracking products yields were a function of both metal (Ni and Pt) content and conversion. Whatever n-decane conversion, monobranched isomers were found to be predominant. Besides, up to 10% conversion, the cracked products were not produced in significant amounts. For a time on stream of 100 min, the best results (47% conversion and 56% isomerization selectivity) were obtained at 250 °C over the catalyst containing 12% Ni, 10% W and 0.2% Pt).

Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts

Activation procedures of Ni-W-Pt based catalysts, prepared by means of a hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance. The chemical composition of the prepared solids have bas characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (NixPty) catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity positively while opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion.

Improved sulfated zirconia isomerization catalyst

In this work, the catalytic behavior of Pt–Ni–WOx supported on amorphous silica–alumina catalysts, prepared by means of a sol–gel technique was tested by hydroisomerization of n-hexane in a continuous fixed-bed reactor operating at atmospheric pressure. Temperature-programmed desorption of ammonia (TPDA), temperature-programmed reduction, BET and atomic absorption spectroscopy techniques were used to characterize the catalysts. The results revealed that both catalytic activity and surface acidity of these solids is strongly dependent on their calcination and reduction temperatures. Besides, the collected data showed that platinum interacts with tungsten and this interaction depends on the pretreatment conditions.

Effect of pretreatment conditions on the catalytic performance of Ni–Pt–W supported on amorphous silica–alumina catalysts

Abstract Activation procedures of Ni-W-Pt based catalysts, prepared by means of a hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n -hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO 2 /Al 2 O 3 and H 2 / n -hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance. The chemical composition of the prepared solids have bas characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (Ni x Pt y ) catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. Moreover, the obtained results on (Ni 12 Pt 0,4 ) AC catalyst showed that the SiO 2 /Al 2 O 3 ratio and H 2 partial pressure affect isomerization selectivity positively while opposite effect was observed for activity (conversion). In addition, the main products in n -hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion.