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碳酸二甲酯(DMC)是一种应用极其广泛的绿色化工产品,其中经济、绿色的甲醇氧化羰基化合成DMC工艺极具工业前景,而Y分子筛负载铜(CuY)是有效催化剂之一.众所周知,CuY催化剂上的Cu~(+)是催化活性中心.Cu~(+)催化活性中心的引入方式用两种:(1)CuCl直接与HY分子筛固相离子交换;(2)Cu~(2+)与NaY分子筛溶液离子交换,然后Cu~(2+)自还原生成活性中心Cu~(+).在无溶剂条件下制备CuY催化剂时,载体HY分子筛中的可交换位H+量是决定催化剂CuY氧化羰基化催化性能的关键因素.文献通过以不同硅铝比的HY分子筛为载体制备的催化剂CuY,研究铜离子可交换位H+量对氧化羰基化的影响,然而,硅铝比的不同也直接影响了分子筛骨架的组成、Si–O–Al的键角、甚至影响了Al~(3+)的分散度,这些因素都直接影响了CuY催化剂活性.因此,研究NaNH_4Y分子筛载体中的可交换位(NH_4~+)的量与CuY催化剂活性间的关系具有非常重要的意义.本文将NaY分子筛与不同浓度的NH_4NO_3溶液进行离子交换,制得具有不同NH+4交换度的NaNH_4Y分子筛,以其为载体,以具有易升华、易分解性质的乙酰丙酮铜Cu(acac)2为铜源,在无溶剂条件下,高温热处理二者固相混合物,NaNH_4Y分子筛中的NH_4~+与Cu(acac)_2中的Cu~(2+)发生了离子交换,Cu~(2+)进一步发生自还原生成活性中心Cu~(+),成功地制备了完全无氯的CuY催化剂,应用于催化常压甲醇氧化羰基化合成DMC过程,研究NaNH_4Y分子筛中的铜离子可交换位NH_4~+与催化剂CuY催化性能间的关系.通过各种表征及对CuY催化剂在甲醇氧化羰基化过程中催化活性分析发现,Y分子筛经过NH_4NO_3溶液离子交换及催化剂的制备过程,其八面沸石结构和孔道保持良好.以未经过离子交换的NaY负载的CuY催化剂上的铜物种完全以CuO形式存在,且没有催化活性.随着NH_4~+交换度增加,CuY催化剂表面CuO含量逐渐降低,而活性中心Cu~(+)含量逐渐增加,且其催化活性也随之增加.当NH_4~+交换度趋于极限值时,CuY催化剂中Cu~(+)含量达最大,其催化活性也达最佳,DMC的时空收率和选择性分别为267.3mg/(g·h)和68.5%,甲醇转化率为6.9%.因此,无溶剂条件下,以NaNH_4Y分子筛为载体,Cu(acac)_2为铜源,制备完全无氯CuY催化剂时,NH_4~+是形成Cu~(+)活性中心的必须条件,且NH_4~+交换度直接影响催化剂CuY的催化活性.
Dimethyl carbonate (DMC) is a widely used green chemical product, among which the economical and green methanol oxidative carbonylation to synthesize DMC process has great industrial prospect, while Y zeolite CuY is one of effective catalysts. , Cu ~ (+) on the CuY catalyst is the active site of catalysis.Cu ~ (+) catalytic activity centers are introduced in two ways: (1) solid state ion exchange of CuCl with HY molecular sieve; (2) +) Ion exchange with NaY zeolite solution, and then Cu ~ (2+) self-reduction to generate active center Cu ~ (+) .In the preparation of CuY catalyst without solvent, the amount of exchangeable site H + CuY Oxidative Carbonylation Catalytic Properties of CuY Catalysts Oxidative Carbonylation Catalysts Oxidative Carbonylation Catalysts Oxidative Carbonylation Catalysts Oxidative Carbonylation Catalysts Oxidative Carbonylation Catalysts Oxidative Carbonylation Directly affects the composition of molecular sieve framework and the bond angle of Si-O-Al, and even affects the dispersion of Al 3+, all of these factors have a direct impact on the activity of CuY catalyst.Therefore, the study of exchangeable NaNH 4 Y molecular sieve carrier The amount of (NH_4 ~ +) and CuY catalyst activity between Department of NaY zeolite with different concentrations of NH_4NO_3 solution for ion exchange, NaNH4Y molecular sieves with different NH +4 exchange degrees were prepared, as its carrier, with easy sublimation, easy decomposition of acetylacetone Copper (acac) 2 is a copper source, and the solid phase mixture is heat treated at high temperature without solvent. NH_4 ~ + in NaNH4Y zeolite and Cu ~ (2+) in Cu (acac) Cu 2+ is further reduced from Cu 2+ to Cu 2+, and a completely chlorine-free CuY catalyst has been successfully prepared for the oxidative carbonylation of methanol to synthesis of DMC. The effects of copper ion on NaNH 4 Y zeolite The relationship between the exchangeable sites NH_4 ~ + and the catalyst CuY catalytic properties was studied.According to various characterizations and the analysis of the catalytic activity of CuY catalysts in the oxidative carbonylation of methanol, it was found that the Y zeolite was ion-exchanged by NH_4NO_3 solution and the catalyst preparation process. The zeolite structure and the pores were well maintained.The copper species on the CuY catalyst supported by NaY without ion exchange existed completely as CuO and had no catalytic activity.With the increase of exchange degree of NH 4 +, the CuY catalyst surface The content of CuO gradually decreased while the content of Cu ~ (+) increased gradually and the catalytic activity increased accordingly.When the NH_4 ~ + exchange rate reached the limit value, the content of Cu ~ (+) reached the maximum in CuY catalyst, The catalytic activity was the best, the space time yield and selectivity of DMC were 267.3mg / (g · h) and 68.5% respectively, and the conversion of methanol was 6.9% .Therefore, under the condition of no solvent, NaNH 4 Y zeolite was used as carrier, Cu (acac) _2 is a copper source, NH_4 ~ + is a necessary condition for the formation of Cu ~ (+) active sites in the preparation of completely CuI-free CuY catalyst, and the exchange degree of NH_4 ~ + has a direct effect on the catalytic activity of CuY.