Synthesis Of Hierarchical Zeolite Supported Ni Catalysts And Their Application For Lipid Hydrodeoxygenation

With the increasing needs in fossiol energy resource,it attracts great interest in exploring the renewable resource,especially in the field of converting of biomass into liquid fuels.Lipid,as considered a renewable biomass,can be converted high-grade liquid fuels via several routes,i)transesterification of lipid to produce fatty methyl ether,ii)catalytic cracking,and iii)hydrodeoxygenation.Due to the high oxygen contents and low calorific values,the fatty acid monoester cannot be directly used for engines.While uncontrollable cracking reactions lead to low yields of hydrocarbons,the hydrodeoxygenation technique shows to be more feasible.However,the low rates in hydrodeoxygenation of lipid using bifunctional metal/acid catalysts limit its large-scale industrial application.Zeolites supported metal catalysts are highly efficient for the hydrodeoxygenation reactions.With respect to construcing the effective metal/acid catalysts,the sizes of metal nanoparticles are too large to enter into the micropores of zeolites,and thus,only limited external surfaces can be utilized for loading metals.Furthermore,the transition metal nanoparticles trend to aggregate at harsh reaction conditions,leading to low activities and fast deactivation.On the other sides,the contact of triglyceride with the active sites is also problematic,as the heavy molecules cannot pass though the micropores and then reacts with the active sites.Therefore,it is urgent to develop methods in preparing metal supported catalysts with high loading and high dispersion,in order to increase the hydrodeoxygenation rates.It deals with two aspects,one is to design and preparation of hierachical zeolites,and the other is to develop the methods for introducing metal nanoparticles.It contains four parts:（1）.Construction of intercrystalline mesoporous（d=25 nm）nano-HBEA zeolite supported Ni catalyst and its application in hydrodeoxygenation of palm oilUsing nano size HBEA zeolite as parent material,we utlize the"up to down"method to produce the mesopores,treating with basic solutions（TPAOH/NaOH and Na₂CO₃）,vapor steaming,and soft template promoted NaOH leaching（CTAB/Na OH）.The TPAOH/NaOH introduction led to formation of more homogeneously dispersed inter-mesopores.TPA⁺is bound to the HBEA surface,and thus prevents deep corrosion of the specific external structure and works as a suitable pore-directing agent.After Ni incorporated on the HBEA,it displays a higher HDO rate for palm oil comparing untreated sample.（2）.Synthesis of intracrystalline mesoporous（d=8 nm）HBEA zeolite loaded Ni nanoparticles and its application in hydrodeoxygenation of drainage oilWe adopt the"down to up"method to sythesis the hierachical HBEA-MS zeolite,using PDADMA as a dual-functional template,where the quaternary ammonium group plays the role of a structure-directing agent for forming the BEA structure and imparting a disordered intra-mesopore structure after removal of the template.Large external surface and 8 nm mesoporous are more conducive to encapsulation of metallic nickel.The architecture of relative position of the Ni nanoparticles and support is directly revealed by ultrathin sections transmission electron microscopy and N₂ sorption measurements,presented together with the indirect evidences of temperature programmed reduction of H₂ and IR spectroscopy of adsorbed CO.In comparison to such an advantageous structure of metal and support,the Ni nanoparticles are more commonly deposited on the limited external surface or inter-mesopores of commercial HBEA carriers.As expected,the catalyst leads to a significantly high initial rate of 38 g?g^-1?h^-1 and highly selective octadecane formation（96%yield）from stearic acid conversion.Consequently,high activity and stable durability are realized for four recycling runs of drainage oil hydrodeoxygenation with the newly developed Ni/HBEA-MS.（3）.Preparation of intra-crystalline mesoporous HUSY hierachical zeolite（d=10,25 and 45 nm）supported Ni catalyst and its application in hydrodeoxygenation of palm oilHierarchical H-style ultra-stable Y（HUSY）zeolites with abundant interconnected mesopores（10,25,45 nm mesopore sizes）have been prepared using a sequential post-synthesis strategy that includes steaming dealumination and mixed-alkali desilication.The steaming treatment generates a broad size range of intra-mesopores（around 25 and 45 nm）.PI/NaOH treatment of HUSY-2 zeolite produce 10 nm mesopore.Though the N₂ adsorption–desorption isotherms,XRD,²⁹Si-NMR,²⁷Al-NMR,TEM and SEM characterization of supports and catalsyts,differences in treatments with tetrapropylammonium hydroxide/sodium hydroxide and pyridine/sodium hydroxide treatments are attributed to the fact that the pyridine molecule（0.54 nm）can pass through the supercages（0.74 nm）to protect the zeolite framework from deep desilication,whereas the tetrapropylammonium hydroxide molecule（0.85 nm）is adsorbed only on the external surface.Eventually,a HUSY zeolite with a high external surface area,inter-connectedness and hierarchical mesopores（10,25,and 45 nm）is prepared by initial high-temperature steaming,which is followed by desilication using a mixed alkali solution containing pyridine and sodium hydroxide.High-dispersion（5.5%）,high-content（35 wt%）,small Ni nanoparticles（4.9±1.2 nm）are loaded onto and into the external surface areas and interpores of the hierarchical HUSY by the deposition–precipitation method.The resultant Ni/HUSY-4 shows an ultra-high efficiency in the hydrodeoxygenation of fatty acids,esters,and palm oil,and achieves high initial rates(60 g?g^-1?h^-1)and a high C₁₈ alkane selectivity（96%）,which may be attributed to the enhanced Br?nsted acid and adjacent Lewis acid（confirmed by the ¹H DQ MAS NMR spectrum）together with the substantial dispersive Ni nanoparticles loaded onto/into the interconnected pores of the hierarchical HUSY support.（4）.Introducing controllable hydrothermal synthesis of hierachical core-shell Ni/HBEA catalyst for hydrodeoxygenation of lipidsIn this section,we have developed a new method（hydrothermal）of loading metal,and compared with the traditional impregnation and deposition precipitation.The method simulates the hydrothermal synthesis of zeolite,the Ni salt was added into the buffer solution with NH₄Cl and NH₃?H₂O.Buffer solution ensures that the pH of the solution is constant,and the support can be desilicated under mild experimental conditions.If the rate of desilication is too fast,the structure of zeolite would be collapsed,and the thermodynamically controlled 2:1 Ni₃Si₄O₁₀（OH）₂ Nickel silicate trends to generate.The obtained HDO rate(54 g?g^-1?h^-1)with Ni/HBEA prepared by a buffer solution via a green hydrothermal approach was much higher than the reported highest rate catalyzed by a Ni/HBEA-MS(38 g?g^-1?h^-1).Due to the use of alkaline buffer solution,a large amount of alkaline waste liquid will be generated during catalyst preparation.In order to solve this problem,we prepared the catalyst by directly mixing the zeolite with nickel salt solution.We explored the influence of different metal precursors on nickel loading.First,hydroxyl ions produced from the hydrolysis of nickel acetate in turn facilitate the cleavage of Si–O–Si bonds,leading to the formation of silicate ions,and combine with nickel ions to produce nickel phyllosilicate（fast step）;the subsequent slow step is the acid catalyzed hydrolysis of Al–O bonds from the Si–O–Al groups.This causes a low nickel loading rate,and it is probably due to the reduced exposure of the silanol framework.In the process,the waste water is re-used and the procedure is amenable to scale-up;it is suggested that WAWB salt precursors can efficiently incorporate Ni onto the zeolitic supports after repeated runs.Compared to those obtained via conventional impregnation（IW）and deposition–precipitation（DP）methods,Ni/HBEA-HT dispalyed a higher activity and more stablity HDO performance.