Synthesis of Ordered Cubic Periodic Mesoporous Silica with High Hydrothermal Stability

1 Introduction Since its first discovery in 1992, ordered mesoporous silica material with large pore size, high surface area, and high pore volume has attracted great attention for the potentially wide application in catalysis, adsorption, separation, and ion exchange, etc. However, the poor hydrothermal stability of mesoporous silica has limited its wide application in industry. Therefore, in the last 10 years, many studies have been dedicated to improving the hydrothermal stability of mesoporous silica. Xiao et al.

Effects of impregnation sequence on the NH_(3)-SCR activity and hydrothermal stability of a Ce-Nb/SnO_(2) catalyst

Hydrothermal stability is crucial for the practical application of deNO_(x)catalyst on diesel vehicles,for the selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR).SnO_(2)-based materials possess superior hydrothermal stability,which is attractive for the development of NH_(3)-SCR catalyst.In this work,a series of Ce-Nb/SnO_(2)catalysts,with Ce and Nb loading on SnO_(2)support,were prepared by impregnation method.It was found that,the NH_(3)-SCR activities and hydrothermal stabilities of the Ce-Nb/SnO_(2)catalysts significantly varied with the impregnation sequences,and the Ce-Nb(f)/SnO_(2) catalyst that firstly impregnated Nb and then impregnated Ce exhibited the best performance.The characterization results revealed that CeNb(f)/SnO_(2)possessed appropriate acidity and redox capability.Furthermore,the strong synergistic effect between Nb and Sn species stabilized the structure and maintained the dispersion of acid sites.This study may provide a new understanding for the effect of impregnation sequence on activity and hydrothermal stability and a new environmental-friendly NH_(3)-SCR catalyst with potential applications for NO_(x)removal from diesel and hydrogenfueled engines.

Possible negative influences of increasing content of cerium on activity and hydrothermal stability of Rh/ceria-zirconia three-way catalysts

The activity and hydrothermal stability of the Rh/Ce_(x)Zr_(1-x)O_(2)(x=0,0.05,0.3,0.5) model three-way catalysts for gasoline vehicle emissions control were investigated in this work.Among the Rh/Ce_(x)Zr_(1-x)O_(2) samples with different Ce/Zr ratios,the Rh/ZrO_(2) sample exhibits a significantly better activity and hydrothermal stability than the rest of the samples.The impacts of having more Ce components in the Rh/Ce_(x)Zr_(1-x)O_(2) catalysts are associated with the strong Rh-O-Ce interaction that tends to over stabilize the rhodium species.A significant amount of such rhodium atoms can be found in the bulk of the support oxides after a hydrothermal aging at 1050℃ with 10% H_(2)O in air for 12 h.Differently,the sintering of rhodium on the surface of Rh/ZrO_(2) catalysts is the main reason for the catalyst deactivation during the hydrothermal aging.These findings provide an example where high dispersion of supported metal induced by strong metal-support interactions does not necessarily lead to high catalytic activity.

Nature of cerium on improving low-temperature hydrothermal stability of SAPO-34

To probe the function of Ce on enhancing low-temperature stability of SAPO-34,Ce/SAPO-34 with different Ce contents was prepared via one-pot method and further treated at 70℃in 80%relative humidity for 24 h.The structural results prove that the one-pot synthesis is an effective way to introduce Ce(Ce<0.325 wt%)without influencing micro-structural and chemical composition.The lowtemperature hydrothermal stability of Ce/SAPO-34 is enhanced by Ce loading.More than 92%CHA structure and total acidity are maintained over 0.188 wt%Ce/SAPO-34,while only about 20%of that left on pure H/SAPO-34.As Ce exists as Ce^(3+)at exchange sites on the surface of SAPO-34,the results of the linear relationship between protected surface acidity and structure/acidity conservation manifest that Ce^(3+))effectively hinders the structural collapse.This study provides new insight into surface acidity protection for solving the problem of low-temperature hydrothermal stability of SAPO-34.

Activity and hydrothermal stability of CeO_2–ZrO_2–WO_3 for the selective catalytic reduction of NO_x with NH_3

A series of CeO2–ZrO2–WO3（CZW）catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction（SCR）of NO with NH3 over a wide temperature of 150–550℃.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H2O.The fresh catalyst showed above 90% NOx conversion at 201–459℃,which is applicable to diesel exhaust NOx purification（200–440℃）.The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures（below 300℃）,while the activity was notably enhanced at high temperature（above 450℃）.The aged CZW catalyst（hydrothermal aging at 700℃ for 8 hr）showed almost 80% NOx conversion at 229–550℃,while the V2O5–WO3/TiO2 catalyst presented above 80% NOx conversion at 308–370℃.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO2–ZrO2 solid solution,amorphous WO3 phase and optimal acidity.In addition,the formation of WO3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.

Enhanced hydrothermal stability of Cu-SAPO-34 with an ultrathin TiO_(2)coated by atomic layer deposition for NH3-SCR

Reducing pollution and carbon emissions is an important step toward peaking CO_(2)emissions before 2030 and reaching carbon neutrality before 2060,and heavy diesel vehicle pollution,particularly nitrogen oxides(NOx)emissions,is an essential part.CuSAPO-34 is a CHA-type small pore molecular sieve with excellent ammonia(NH_(3))selective catalytic reduction(NH_(3)-SCR)catalytic activity,but it cannot be stored or applied because of severe degradation caused by low-temperature hydrothermal aging.To improve the hydrothermal stability,TiO_(2)was coated on the surface of Cu-SAPO-34 by the ALD method to form a uniform nanolayer.Though this ultrathin TiO_(2)nanolayer has little effect on NH_(3)-SCR catalytic activity of Cu-SAPO-34,the resistance to low-temperature hydrothermal aging in liquid water at 80℃for 24 h has greatly been improved.A study carried out by SEM,XRD,NH_(3)-TPD,and EPR,showed that the ultra-thin TiO_(2)nanolayers were covered uniformly and hydrolysis of frameworks silicon and the migration of Cu^(2+)was retarded.This method has some implications for the future preparation of highly robust Cu-SAPO-34 catalysts for industrial applications.This research could inspire the development of highly robust CuSAPO-34 catalysts to control the NOx emissions from diesel engines.

Catalytic hydrothermal liquefaction of microalgae over metal incorporated mesoporous SBA-15 with high hydrothermal stability

Hydrothermal liquefaction(HTL)is one of the most promising technologies for conversion of microalgae,and catalysts with high hydrothermal stability are required for controllable HTL.In this article,SBA-15 incorporated with transition metals(Ni,Pd,Co and Ru)were synthetized via double-template method for catalytic HTL of microalgae.The results showed that metal incorporated SBA-15 represented high hydrothermal stability at 613 K.The incorporated Ni,Co and Ru was dispersed in SBA-15 enhancing the hydrothermal stability.The catalysts greatly influenced the chemical composition of the obtained bio-oil,which contained a higher percentage of furfural derivatives and a lower content of fatty acids and N-containing compounds,thus bio-oil quality was improved significantly.Higher hydrothermal stability and specific surface areas of Co-SBA-15 contribute to the highest preformation with 78.78%conversion and 24.11 wt%bio-oil yield.Metal incorporated SBA-15 provides a potential application for biomass conversion in high-temperature aqueous phase.

Hydrothermal stability of MO_x-Ce_(0.75)Zr_(0.25)O_2 catalysts for NO_x reduction by ammonia

Various acidic components（MOx：phosphate,sulfate,tungstate and niobate） were loaded on Ce0.75 Zr0.25 O2 powders by an impregnation method.The as-prepared catalysts were hydrothermally treated at 760 oC for 48 h in air containing 10 vol.% H2 O to obtain the aged catalysts.The catalysts were characterized by X-ray diffraction,Fourier transform infrared spectroscopy,H2 programmed-reduction,NH3 adsorption and deNOx activity measurements.The results showed that,among the catalysts investigated,the phosphated Ce0.75 Zr0.25 O2 catalyst showed the highest hydrothermal stability.The remained high acidity of the phosphated catalyst with moderate redox property helped to maintain the excellent NH3-SCR activity of hydrothermally aged catalyst.Cerium tungstate led to the poor redox property of the tungstated catalyst although the acidity of catalyst was still high.The decomposition of sulfates at temperatures higher than 600 °C restrained the usage of sulfated catalysts in high temperature conditions.The overall dehydration of niobate to niobium oxides led to the low acidity of hydrothermally aged Nb2 O5-Ce0.75 Zr0.25 O2 catalyst.

Promotional effect of ion-exchanged K on the low-temperature hydrothermal stability of Cu/SAPO-34 and its synergic application with Fe/Beta catalysts

K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging.The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction(SCR)activity.For the fresh Cu/SAPO-34 catalysts,K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites.After hydrothermal aging,the structural integrity and amount of active sites decreased on pure Cu/SAPO-34.While the K-loaded catalysts showed improved chabazite structure,acidity,and active site conservation with increasing K loading.However,although the 0.7 wt%K catalyst maintained the same crystallinity,active site abundance,and low-temperature SCR activity as the fresh catalyst upon aging,an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Brönsted acid sites.To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature,Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34,and a wide active temperature window of SCR activity was obtained.Thus,our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.

Optimization of Hybrid Crystal with SAPO-5/34 on Hydrothermal Stability for deNOx Reaction by NH3

In order to deal with the challenge of the hydrothermal deactivation of selective catalytic reduction of NO by NH3(NH3-SCR)catalyst and extend its lifetime,a novel Cu/SAPO-5/34 catalyst was prepared,and it almostmaintains its deNOx performance with a high conversion rate of 90%NO,between 175℃and 400℃after under-going the rigorous treatment at 800℃for 12 h.Thus,Cu/SAPO-5/34 is more recalcitrant to the high-temperature hydrothermal deactivation than Cu/SAPO-34.Besides,the formation of N20 is always below 3×10^-6(3 ppm)during the whole reaction temperature.performing an advanced catalytic selectivity.The effect of high-temperature hvdro-thermal treatment on the morphology,structure and texture property,the acid sites,as well as the active copper spe cies were investigated.These characterizations manifest that the optimized high-temperature hydrothermal stability is associated closely with the good structural stability over Cu/SAPO-5/34-HT.which facilitates to preserve reaction sites,and then showing the better hydrothermal stability than Cu/SAPO-34.

A highly hydrothermal stable copper-based catalyst for catalytic wet air oxidation of m-cresol in coal chemical wastewater

Catalytic wet air oxidation(CWAO) can degrade some refractory pollutants at a low cost to improve the biodegradability of wastewater. However, in the presence of high temperature and high pressure and strong oxidizing free radicals, the stability of catalysts is often insufficient, which has become a bottleneck in the application of CWAO. In this paper, a copper-based catalyst with excellent hydrothermal stability was designed and prepared. TiO_(2) with excellent stability was used as the carrier to ensure the longterm anchoring of copper and reduce the leaching of the catalyst. The one pot sol–gel method was used to ensure the super dispersion and uniform distribution of copper nanoparticles on the carrier, so as to ensure that more active centers could be retained in a longer period. Experiments show that the catalyst prepared by this method has good stability and catalytic activity, and the catalytic effect is not significantly reduced after 10 cycles of use. The oxidation degradation experiment of m-cresol with the strongest biological toxicity and the most difficult to degrade in coal chemical wastewater was carried out with this catalyst. The results showed that under the conditions of 140℃, 2 MPa and 2 h, m-cresol with a concentration of up to 1000 mg·L^(-1) could be completely degraded, and the COD removal rate could reach 79.15%. The biological toxicity of wastewater was significantly reduced. The development of the catalyst system has greatly improved the feasibility of CWAO in the treatment of refractory wastewater such as coal chemical wastewater.

Synthesis of AIMCM-41 mesoporous molecular sieves with high stability

Mesoporous molecular sieves AIMCM-41 were synthesized by static hydrothermal crystallization using cetyltrimethylammonium bromide as template, water glass as silica source and pseudoboehmite as aluminum source. The XRD results showed that the prepared AlMCM-41 mesoporous molecular sieves had high relative crystallinity and long-range order. The relative crystallinity was greater than 27% after calcination at 900 ℃ for 2 hours and was still greater than 14% after ageing in steam at 800 ℃ for 2 hours. The results indicated that both thermal and hydrothermal stabilities of the mesoporous molecular sieves AIMCM-41 were good.

Hydrothermal Synthesis and Visible-light Photocatalytic Activities of SnS_2 Nanoflakes

SnS2 nanoflakes were successfully synthesized via a simple hydrothermal process. The as-prepared SnS2 samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, nitrogen adsorption-desorption isotherms, and UV-vis diffuse reflectance spectroscopy（DRS）. The photocatalytic activities of the as-prepared SnS2 nanoflakes under visible light irradiation（λ〉420 nm） were evaluated by the degradation of rhodamine B（Rh B）. The effect of hydrothermal temperatures on the photocatalytic efficiency of as-prepared SnS2 nanoflakes was investigated. The experimental result showed that SnS2 nanoflakes synthesized at the temprature of 160 o had higher photocatalytic efficiency and good photocatalytic stability.

Hydrothermally stable metal oxide-zeolite composite catalysts for low-temperature NO_(x) reduction with improved N_(2) selectivity

Development of hydrothermally stable,low-temperature catalysts for controlling nitrogen oxides emissions from mobile sources remains an urgent challenge.We have prepared a metal oxide-zeolite composite catalyst by depositing Mn active species on a mixture support of CeO_(2)/Al_(2)O_(3) and ZSM-5.This composite catalyst is hydrothermally stable and shows improved low-temperature SCR activity and significantly reduced N_(2)O formation than the corresponding metal oxide catalyst.Comparing with a Cu-CHA catalyst,the composite catalyst has a faster response to NH_(3) injection and less NH_(3) slip.Our characterization results reveal that such an oxide-zeolite composite catalyst contains more acidic sites and Mn^(3+)species as a result of oxide-zeolite interaction,and this interaction leads to the generation of more NH_(4)^(+)species bound to the Br?nsted acid sites and more reactive NOxspecies absorbed on the Mn sites.Herein,we report our mechanistic understanding of the oxide-zeolite composite catalyst and its molecular pathway for improving the low-temperature activity and N_(2) selectivity for NH_(3)-SCR reaction.Practically,this work may provide an alternative methodology for low-temperature NO_(x) control from diesel vehicles.

Hierarchical ZSM-11 with intergrowth structures:Synthesis,characterization and catalytic properties

Hierarchical ZSM-11 microspheres with intercrystalline mesoporous properties and rod-like crystals intergrowth morphology have been synthesized using a spot of tetrabutylammonium as a single template.XRD,FTIR,SEM,TEM and N2 adsorption analysis revealed that each individual particle was composed of nanosized rod crystals inserting each other and the intercrystalline voids existing among rods gave a significant mesopore size distribution.Steam treatment result demonstrated the excellent hydrothermal stability of samples.Various crystallization modes including constant temperature crystallization (one-stage crystallization) and two-stage temperature-varying crystallization with different 1st stage durations were investigated.The results suggested that the crystallization modes were mainly responsible for the adjustable particle size and textural properties of samples while the small amount of tetrabutylammonium bromide was mainly used to direct the formation of both ZSM-11 framework and its intergrowth morphology.Furthermore,the performance of optimal ZSM-11 as an active component for the catalytic pyrolysis of heavy oil was also investigated.Compared with the commercial pyrolysis catalyst,the hierarchical ZSM-11 catalyst exhibited a high selectivity to desired products(LPG+gasoline+diesel),as well as a much lower dry gas and coke yield,plus a high selectivity and yield of light olefins(C=3 C=4)and very poor selectivity to benzene.Therefore,fully open micropore-mesopore connectivity would make such hierarchically porous ZSM-11 zeolites very attractive for applications in clean petrochemical catalysis field.

A high-surface-area silicoaluminophosphate material rich in Brnsted acid sites as a matrix in catalytic cracking

A transparent gel-like mesoporous silicoaluminophosphate material （SAP） with molar ratio of Si/Al = 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus （P） into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area （up to 492 m2/g） exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Br／＂{o}nsted acidic sites （up to 48.44 μmol/g） and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L （Lewis acid/Br？nsted acid） increased to 1.15. The performances of samples as matrices for the catalytic cracking of heavy VGO were investigated. At 520 ℃, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity （2.86%） than conventional FCC matrices, such as kaolin and amorphous silica-alumina.

Application of New Heavy Metals Resistant Porous Binder Material Used in Fluid Catalytic Cracking Reaction

A novel porous binder was obtained from acid-treated kaolin. This new binder possessed abundant meso/macropores, good hydrothermal stability and heavy metal resistance. The prepared catalyst using new binder featured low attrition index and large pore volume. The catalysts were contaminated with Ni, V, and tested in a fixed-fluidized bed reactor unit. In comparison with the reference sample, the oil conversion achieved by the above-mentioned catalyst increased by 3.50 percentage points, and heavy oil yield decreased by 2.86 percentage points, while the total liquid yield and light oil yield increased by 2.82 percentage points and 0.79 percentage points, respectively. The perfect pore structure, good hydrothermal stability and heavy metal resistant performance of new binder were the possible causes leading to its outstanding performance.

Effect of LaPO_(4) Introduction as a Vanadium Trap for Preventing USY Zeolite Destruction

The use of lanthanum phosphate as a vanadium trap for preventing destruction of USY zeolite was studied.The effect of deposited vanadium on the hydrothermal destruction of zeolite was investigated by the solid-state NMR technique.LaPO4 species can inhibit the zeolite framework structure from being collapsed by vanadium after steaming treatment.The EPR results show the oxidation-reduction reaction in LaPO4 and V2O5 system and inhibition of zeolite destruction by V5+.The catalysts prepared from USY and LaPO-USY zeolites were also tested in the catalytic reactions of heavy oil.The assessment results indicated that the USY modified with LaPO4 could bring about remarkably high dehydrogenation ability.

Nano-sized alumina supported palladium catalysts for methane combustion with excellent thermal stability

Pd/Al_(2)O_(3)catalysts supported on Al_(2)O_(3)of different particle sizes were synthesized and applied in methane combustion.These catalysts were systematically characterized by Brunauer-Emmett-Teller (BET),X-ray diffraction (XRD),high resolution-transmission electron microscopy (HR-TEM),high-angle annular dark?eld-scanning transmission electron microscopy (HAADF-STEM),H_(2)-temperature-programmed reduction (H_(2)-TPR),O_(2)-temperature-programmed oxidation (O_(2)-TPO),X-ray photoelectron spectroscopy (XPS),and X-ray absorption?ne structure (XAFS).The characterization results indicated that nanosized Al_(2)O_(3)enabled the uniform dispersion of palladium nanoparticles,thus contributing to the excellent catalytic performance of these nano-sized Pd/Al_(2)O_(3)catalysts.Among them,Pd/Al_(2)O_(3)-nano-10 (Pd/Al_(2)O_(3)supported by alumina with an average particle size of 10 nm)showed superior catalytic activity and stability for methane oxidation under harsh practical conditions.It maintained excellent catalytic performance for methane oxidation for50 hr and remained stable even after harsh hydrothermal aging in 10 vol.%steam at 800℃ for 16 hr.Characterization results revealed that the strong metal-support interactions and physical barriers provided by Al_(2)O_(3)-nano-10 suppressed the coalescence ripening of palladium species,and thus contributed to the superior sintering resistance of the Pd/Al_(2)O_(3)-nano-10 catalyst.

Highly Durable MIL-96 Membranes via a One-step Active γ-Alumina Conversion Strategy for Gas Separation

Metal-organic frameworks(MOFs)are attractive in membrane separation due to their special pore structure and suitable aperture size.The fabrication of defect-free and robust MOF membranes with excellent durability is highly demanded but remains challenging.In this work,we report a one-step activeγ-alumina conversion strategy for the facile and reliable fabrication of an MIL-96 membrane.In this case,theγ-Al_(2)O_(3) sol was dip-coated and sintered on theα-Al_(2)O_(3) disc as the active aluminum source and substrate for the nucleation and growth of MOF.A continuous and well-intergrown MIL-96 membrane was generated with exceptional stability due to the strong adhesion to the substrate.The resultant MIL-96 membrane yielded a satisfactory H_(2)/CO_(2) permselectivity and high-temperature resistance,delivering a selectivity of 12.35 with H_(2) permeance of 6.20×10^(−7) mol·m^(−2)·s^(−1)·Pa^(−1) at 150℃.Moreover,the probe membrane presented remarkable durability and recyclability under harsh hydrothermal conditions.This method paves the way for constructing highly stable and selective MOF membranes and could accelerate the development of advanced membrane separation technologies for gas purification and recycling in addressing the severe energy and environmental problems.