Catalytic Performance Of Cu₂O And Cu₂O/TiO₂ For Formaldehyde Ethynylation

1,4-Butynediol?short for BYD?is a versatile basic organic raw chemicals,which is generally synthesized in accordance with the Reppe process by reacting formaldehyde with acetylene.And Cu²⁺ compounds?subsalt or oxide?are the main catalyst precursor and bismuth oxide is usually added into the catalysts for effectively restraining the excessive reduction of Cu²⁺compounds and minimizing cuprene formation.In ethynylation reaction,these initial Cu²⁺ compounds convert to active species?cuprous acetylide?in situ,undergo some complex chemical changes,the detailed process may be speculated as:?1?selective reduction of Cu²⁺ to Cu⁺ by formaldehyde;?2?the formation of cuprous acetylide by Cu⁺ with acetylene.However,the generation of cuprous acetylide is difficult to control and the excessive reduction of Cu²⁺ compounds for Cu0 will promote the formation of cuprene,leading to the decrease of activity and selectivity of catalysts.Therefore,using Cu⁺ compounds as catalyst precursor will be favorable as it can eliminate the complex step(reduction of Cu²⁺ to Cu⁺),and the formation of cuprous acetylide will be controllable.As a type of semiconductor with unique physical and chemical properties,cuprous oxide?Cu₂O?is widely applied in solar energy coversion,gas sensors,biosensors,lithium ion batteries.Furthermore,some works have reported that Cu₂O is catalytically active in many reactions,such as the reduction of NO by CO,photodegradation of organic pollutants,decomposition of water to H₂ and O₂ under visible light,the Rochow reaction,thermal decomposition of ammonium perchlorate,CO oxidation.However,there are few reports about the catalytic application of Cu₂O in ethynylation reaction of formaldehyde for1,4-butynediol synthesis.In this paper,we prepared a series of Cu₂O,combining with the characterization results,we systematically studied the effect of copper sources and NaOH concentration on structure,reducibility and catalyticacitivity of Cu₂O in formaldehyde ethynylation reaction;Furthermore,we studied the support effects of Cu₂O/TiO₂ catalyst in ethynylation reaction of formaldehyde.The major findings of this paper are as follows:1?Cu₂O were successfully synthesized with different copper sources by a simple liquid phase reduction method.The Cu₂O prepared with CuCl₂·2H₂O showed a superior catalytic activity towards 1,4-butynediol synthesis in ethynylation reaction of formaldehyde,as it has unique surfaces that covered with a passive overlayer composed with chloride,leading to less exposed Cu⁺and the poor reducibility eventually.2?A series of Cu₂O was prepared using copper chloride as copper source with the Na OH concentration as variables.NaOH concentration changed particle size and crystallinity,resulting in difference in reducibility and ethynylation property.Medium concentration of NaOH made Cu₂O have appropriate particle size,crystallinity and reacting property and show the superior catalytic performance for formaldehyde ethynylation.3 ? Support effects had a great influence on reducibility and catalytic performance of Cu₂O/TiO₂ catalysts.When the active precursor Cu₂O had weak interaction with TiO₂,Cu₂O was easy to be restored for metallic Cu,resulting in poor catalytic activity.With the gradually increase of the support effects,Cu₂O became increasingly difficult to be reduced.Most of Cu₂O was converted to cuprous acetylide and showed the superior catalytic performance.