Porous Catalyst Carriers Research Articles

3D printing of metal-organic frameworks decorated hierarchical porous ceramics for high-efficiency catalytic degradation

Combination of porous catalyst carriers and high-performance catalysts has attracted increasing attention due to their efficient, reusable and durable characteristics in water purification. Herein, we report a design of three dimensional printed hierarchical porous ceramics that can in-situ load metal-organic frameworks-based catalysts by facile hydrothermal treatment. The resultant supported catalysts with hierarchical features are capable to completely decompose organic dyes based on Fenton reaction, exhibiting the highest removal efficiency and dye degradation rate (kobs) of 99.68% and 0.2915 min−1, respectively. Moreover, its catalytic degradation rates are much greater than other reported Fe-/Cu-based metal organic framework heterogeneous Fenton catalysts. The outstanding catalytic degradation performance towards organic dyes is ascribed to their large surface area, numerous active sites, and hierarchical matter transport channels in the interconnected porous networks. Also, the three-dimensional (3D) printed hierarchical porous catalysts demonstrate lasting degradation efficiency (>75%) over 50 reusable cycles. More importantly, two types of catalytic reactors, such as 3D-printed catalytic filter and impeller agitator, have been successfully manufactured by the present strategy. This work uncovers a novel strategy that not only enables complex and efficient multiscale porous 3D catalysts, but also presents considerable prospects in the aspects of functional devices for water treatment.

Hierarchically porous tungstophosphoric acid/silica hybrid for high performance vis-light photocatalysis

A high performance photocatalyst was prepared by loading tungstophosphoric acid (H3PW12O40) in hierarchically porous silica. Several kinds of dye pollutants, such as neutral red, rhodamine B and fuchsin basic, were efficiently degraded under visible light irradiation by this catalyst. The hierarchically porous material was characterized via SEM, FT-IR, N2 adsorption–desorption isotherms and X-ray fluorescence spectrometry (XRF). This kind of photocatalyst had a relative large surface area, pore diameter and pore volume. The degradation kinetics and degradation products were also investigated to clarify the degradation process. The dyes could be facilely and quickly bleached and mineralized (ca. 97.80% of removal for fuchsin basic in 80min), and there were no small organics detected in the main degradation products. Comparing with other porous catalyst carriers (MCM-41 and SBA-15), the hierarchically porous structure was considered to be an important factor to improve the molecular diffusion in the heterocatalysis process and enhance the degradation efficiency. Additionally, this hierarchically porous catalyst was very stable and easy to be separated from the reaction solution for reuse.

Dynamics of fragmentation of catalyst carriers in catalytic polymerization of olefins

A model capable to perform first principle based modeling of early stages of the growth of catalyst/polymer particles in catalytic polymerization of olefins is introduced. The polymer, the porous catalyst carrier and the void phase of the particle are discretized into micro-elements of several types coupled by force and mass transport interactions. We employ the introduced morphogenesis model to address selected experimental observations of the fragmentation stage of particle growth. Specifically, the capabilities of the model are demonstrated on the “shrinking core” and the “continuous bisection” fragmentation mode of porous catalyst carriers.

Oxidative Conversion of Methane to Syngas over Nickel Supported on Commercial Low Surface Area Porous Catalyst Carriers Precoated with Alkaline and Rare Earth Oxides

Partial oxidation of methane to CO and H2at very small contact times (4.8 ms at STP) over different supported Ni-catalysts at 700 and 800°C, CH4/O2ratio in feed of 1.8 and gas space velocity of 5.2×105cm3·g−1·h−1(at STP) has been investigated. The catalysts were prepared by depositing NiO–MgO on different commercial low surface area porous catalyst carriers (obtained from M/S Norton Co., USA) consisting of refractory compounds (viz. SiO2, Al2O3, SiC, ZrO2, and HfO2) at different concentrations and having different surface properties and also prepared by depositing NiO on the catalyst carriers precoated with different alkaline and rare earth oxides (viz. MgO, CaO, SrO, BaO, Sm2O3, and Yb2O3). The catalysts have been characterized by their TPR by H2from 100 to 900°C, degree of NiO reduction, and H2chemisorption after the catalyst reduction at 900°C. The influence of support (its composition and surface properties), method of NiO and MgO deposition, support precoating agent, loadings of NiO and MgO (as support precoating agent), and calcination temperature on the conversion and selectivity has been studied. The influence of these catalyst parameters on the TPR, degree of NiO reduction, and H2chemisorption on the catalyst has also been studied. The catalyst characteristics are strongly influenced by the support (containing Al2O3and/or SiO2at higher concentrations and having higher surface area), precoating agent, loading of MgO precoat on the support, particularly at lower loadings (below 2 wt%), and also by the catalyst calcination temperature above 900°C. The catalyst prepared by depositing NiO on the commercial supports (except SA-5552 having much higher surface area) precoated with MgO (6±1 wt%) and calcined at 900°C shows excellent performance in the catalytic process (at 800°C) with very high methane conversion (>91%), selectivity (>95%) and CO productivity (>13 mol·g−1·h−1, which is about two orders of magnitude higher than that obtained in steam reforming of methane). However, the conversion and selectivity are reduced drastically when the MgO loading is decreased below 2 wt%, the MgO precoat is replaced by that of SrO or BaO or when the catalyst is calcined above 1050°C.

Oxidative coupling of methane over Sm‐promoted MgO: Influence of composition and preparation conditions

Influences of promoter concentration (or Sm/Mg ratio), precursor for MgO (viz. Mg-acetate, Mg-carbonate and Mg-hydroxide), calcination temperature of Sm-promoted MgO catalyst on the catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different temperatures (650-850°C) and CH 4 /O 2 ratios in feed (2.0-8.0) at a high space velocity (51600 cm 3 /g.h) have been investigated. The catalytic activity/selectivity of Sm-MgO catalysts in the OCM are found to be strongly influenced by the Sm/Mg ratio, precursor used for MgO and catalyst calcination temperature. The catalyst with Sm/Mg ratio of 0.11, prepared using magnesium acetate and magnesium carbonate as a source of MgO and calcining at 950°C, is found to be highly active and selective in the OCM process. A drastic reduction in catalytic activity/selectivity is observed when the catalyst is supported on low surface area porous catalyst carriers, indicating strong catalyst-support interactions.

Oxidative Coupling of Methane over a Sr-Promoted La2O3 Catalyst Supported on a Low Surface Area Porous Catalyst Carrier

Oxidative coupling of methane (OCM) to higher hydrocarbons over Sr-promoted La2O3 supported on commercial low surface area porous catalyst carriers (containing mainly alumina and silica) at 800 and 850 °C and a space velocity of 102 000 cm3·g-1·h-1 has been thoroughly investigated. Effects of support, catalyst particle size, linear gas velocity (at the same space velocity), Sr/La ratio, CH4/O2 ratio in the feed, and catalyst dilution by inert solid particles on the conversion, yield, or selectivity and product ratios (C2H4/C2H6 and CO/CO2) in the OCM process have been studied. The catalysts have been characterized for their basicity, acidity, and oxygen chemisorption by the TPD of CO2, ammonia, and oxygen, respectively, from 50 to 950 °C and also characterized for their surface area. The supported catalysts showed better performance than the unsupported one. The best OCM results (obtained over Sr-La2O3/SA-5205 with a Sr/La ratio of 0.3 at a space velocity of 102 000 cm3·g-1·h-1) are 30.1% CH4 conversion with 65.6% selectivity for C2+ (or 19.7% C2+-yield) at 800 °C (CH4/O2 = 4.0) and 12.8% CH4 conversion with 85.1% selectivity for C2+ (or 10.9% C2+-yield) at 850 °C (CH4/O2 = 16.0). The basicity is strongly influenced by the Sr/La ratio; the supported catalysts showed the best performance for their Sr/La ratio of about 0.3. The methane/O2 ratio also showed a strong influence on the OCM process. However, the influence of linear gas velocity and particle size is found to be small; it results mainly from the temperature gradient in the catalyst. The catalyst dilution has little or no effect on the conversion and selectivity. However, it has beneficial effects for achieving a higher C2H4/C2H6 ratio and also for reducing the hazardous nature of the OCM process because of the coupling of the exothermic oxidative conversion reactions and the endothermic thermal cracking reactions and also due to the increased heat transfer area.

Oxidative Coupling of Methane over Supported La2O3 and La-Promoted MgO Catalysts: Influence of Catalyst−Support Interactions

Methane-to-C{sub 2}-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted MgO catalysts in the oxidative coupling of methane and strong basicity of the catalysts are decreased appreciably when these catalysts are deposited on commonly used commercial low surface area porous catalyst carriers containing Al{sub 2}O{sub 3}, SiO{sub 2}, SiC, or ZrO{sub 2} + HfO{sub 2} as the main components. The decrease in the strong basicity and catalytic activity/selectivity or yield is mostly due to strong chemical interactions between the active catalyst component (viz., MgO and La{sub 2}O{sub 3}) and the reactive components of the catalyst support (viz., Al{sub 2}O{sub 3} and SiO{sub 2}), resulting in the formation of catalytically inactive binary metal oxides on the support surface. However, the influence of support on the activity/selectivity of La{sub 2}O{sub 3} is relatively very small, and also the chemical interactions of La{sub 2}O{sub 3} with the supports (except that containing a high concentration of SiO{sub 2}) are almost absent. The catalyst-support interactions are thus found to be strongly dependent upon the nature (chemical composition) of both catalyst and support. For developing better supported catalysts for the oxidative coupling of methane, supported La{sub 2}O{sub 3} with some promoters shows high promise.

Large enhancement in methane-to-syngas conversion activity of supported Ni catalysts due to precoating of catalyst supports with MgO, CaO or rare-earth oxide

Supported nickel catalysts prepared using commercial sintered low surface area porous catalyst carriers (containing SiO2 and/or Al2O3) precoated with MgO, CaO or rare-earth oxide show very much higher activity, selectivity and productivity in methane-to-syngas conversion reactions, than the catalysts prepared using catalyst carriers without any precoating. Among the precoating metal oxides, the best performance is observed for MgO.

Fatigue behavior of welded aluminium structures

Partial oxidation of methane to CO and H2at very small contact times (4.8 ms at STP) over different supported Ni-catalysts at 700 and 800°C, CH4/O2ratio in feed of 1.8 and gas space velocity of 5.2×105cm3·g−1·h−1(at STP) has been investigated. The catalysts were prepared by depositing NiO–MgO on different commercial low surface area porous catalyst carriers (obtained from M/S Norton Co., USA) consisting of refractory compounds (viz. SiO2, Al2O3, SiC, ZrO2, and HfO2) at different concentrations and having different surface properties and also prepared by depositing NiO on the catalyst carriers precoated with different alkaline and rare earth oxides (viz. MgO, CaO, SrO, BaO, Sm2O3, and Yb2O3). The catalysts have been characterized by their TPR by H2from 100 to 900°C, degree of NiO reduction, and H2chemisorption after the catalyst reduction at 900°C. The influence of support (its composition and surface properties), method of NiO and MgO deposition, support precoating agent, loadings of NiO and MgO (as support precoating agent), and calcination temperature on the conversion and selectivity has been studied. The influence of these catalyst parameters on the TPR, degree of NiO reduction, and H2chemisorption on the catalyst has also been studied. The catalyst characteristics are strongly influenced by the support (containing Al2O3and/or SiO2at higher concentrations and having higher surface area), precoating agent, loading of MgO precoat on the support, particularly at lower loadings (below 2 wt%), and also by the catalyst calcination temperature above 900°C. The catalyst prepared by depositing NiO on the commercial supports (except SA-5552 having much higher surface area) precoated with MgO (6 ± 1 wt%) and calcined at 900°C shows excellent performance in the catalytic process (at 800°C) with very high methane conversion (>91%), selectivity (>95%) and CO productivity (>13 mol·g−1·h−1, which is about two orders of magnitude higher than that obtained in steam reforming of methane). However, the conversion and selectivity are reduced drastically when the MgO loading is decreased below 2 wt%, the MgO precoat is replaced by that of SrO or BaO or when the catalyst is calcined above 1050°C.

A study of the internal diffusion of gases in porous catalysts in the presence of a liquid phase

A new measurement method is proposed for determining the internal diffusion coefficient as a function of the degree of filling of the catalyst pores with the condensing liquid phase. The experimental results are presented for some selected porous catalyst carriers. It is found that upon reaching its dew point the condensate fills up the pores completely, thus strongly reducing diffusion in the gas phase. A modification of the structure of the porous carrier is proposed leading to a considerable enhancement of the diffusion under such operating conditions

Axial dispersion of gas and solid phases in a gas—solid packed column at trickle flow

Axial dispersion of gas and solid phases in a gas—solid packed column at trickle flow, a promising new countercurrent operation, was evaluated using residence time distribution (RTD) experiments. The column was packed with dumped Pall rings, the gas phase was air at ambient conditions and the solid was a porous catalyst carrier. The RTD experiments for the solid phase were carried out using the “perfect pulse method”, while for the gas phase the “imperfect pulse method” was used. The model parameters were calculated by the methods of moments and various parameter optimization methods. At a given solid flow rate axial dispersion of the gas phase decreases with increasing gas velocity and is strongly dependent upon solid mass flux. Axial dispersion of the solid phase is approximately independent of the gas velocity and it is reduced if the solid mass flux is increased. For conditions of practical importance, 2 – 5 and 5 – 15 Pall ring layers correspond to the height of a mixing unit in the gas and solid phase, respectively.