Though ammonia borane NH_(3)BH_(3)(AB)was discovered in the 1950s,it is fair to state that AB as a potential chemical hydrogen storage material was discovered more recently,in the 2000s.Unlike the isoelectronic ethane...Though ammonia borane NH_(3)BH_(3)(AB)was discovered in the 1950s,it is fair to state that AB as a potential chemical hydrogen storage material was discovered more recently,in the 2000s.Unlike the isoelectronic ethane CH_(3)CH_(3),AB is polar;three of its hydrogens are protic(NH_(3)group)and the other three are hydridic(BH_(3)group);the material is solid at ambient conditions owing to dihydrogen N–H^(δ+)…H^(δ−)–B interactions;and AB decomposes from 90℃under thermogravimetric conditions.With such properties,AB has attracted much attention,even though AB in neat form is not suitable for the application mentioned above because it decomposes more than it dehydrogenates.Hence,strategies(based on solubilization,catalysis,chemical doping and nanosizing)aiming at destabilizing AB to make it release pure H_(2)at<100℃have been developed.Beyond the performance targeted for hydrogen storage,this provided us with better understanding of the mechanisms of decomposition.Indeed,studies on thermal decomposition of neat AB have revealed just how complex the mechanisms are(due to the involvement of two possible key intermediates initiating the decomposition,the formation of various volatile products,the existence of counterintuitive homopolar reactions,and the formation of polymeric residues of complex composition,for example).Studies on destabilized AB have provided insights into several mechanistic aspects including the reaction intermediates,the decomposition pathways,and the nature of the residue forming upon the release of 1 and≥2 equiv.H_(2).We presently have a fairly good understanding of the mechanisms of decomposition of AB,which is discussed in more detail below.In that respect,this review focuses firstly on the complexity of thermal decomposition of neat AB,secondly on what we know with regard to thermal decomposition of destabilized AB,and thirdly on all outstanding questions.It is very important to have an excellent knowledge of the reaction mechanisms if technological progress is to be made with AB as a chemical hydrogen storage material.展开更多
Ammonia borane(NH_(3)BH_(3))is a reducing agent,able to trap and convert carbon dioxide.In the present work,we used a reactive solid consisting of a mixture of 90 wt.%of NH_(3)BH_(3)and 10 wt.%of palladium chloride,be...Ammonia borane(NH_(3)BH_(3))is a reducing agent,able to trap and convert carbon dioxide.In the present work,we used a reactive solid consisting of a mixture of 90 wt.%of NH_(3)BH_(3)and 10 wt.%of palladium chloride,because the mixture reacts in a fast and exothermic way while releasing H2 and generating catalytic Pd0.We took advantage of such reactivity to trap and convert CO_(2)(7 bar),knowing besides that Pd0 is a CO_(2)hydrogenation catalyst.The operation(i.e.stage 1)was effective:BNH polymers,and B−O,C=O,C−O,and C−H bonds(like in BOCH_(3)and BOOCH groups)were identified.We then(in stage 2)pyrolyzed the as-obtained solid at 1250℃ and washed it with water.In doing so,we isolated cyclotriboric acid H_(3)B3O6(stemming from B2O3 formed at 1250℃),hexagonal boron nitride,and graphitic carbon.In conclusion,the stage 1 showed that CO_(2)can be‘trapped’and converted,resulting in the formation of BOCH_(3)and BOOCH groups(possible sources of methanol and formic acid),and the stage 2 showed that CO_(2)transforms into graphitic carbon.展开更多
文摘Though ammonia borane NH_(3)BH_(3)(AB)was discovered in the 1950s,it is fair to state that AB as a potential chemical hydrogen storage material was discovered more recently,in the 2000s.Unlike the isoelectronic ethane CH_(3)CH_(3),AB is polar;three of its hydrogens are protic(NH_(3)group)and the other three are hydridic(BH_(3)group);the material is solid at ambient conditions owing to dihydrogen N–H^(δ+)…H^(δ−)–B interactions;and AB decomposes from 90℃under thermogravimetric conditions.With such properties,AB has attracted much attention,even though AB in neat form is not suitable for the application mentioned above because it decomposes more than it dehydrogenates.Hence,strategies(based on solubilization,catalysis,chemical doping and nanosizing)aiming at destabilizing AB to make it release pure H_(2)at<100℃have been developed.Beyond the performance targeted for hydrogen storage,this provided us with better understanding of the mechanisms of decomposition.Indeed,studies on thermal decomposition of neat AB have revealed just how complex the mechanisms are(due to the involvement of two possible key intermediates initiating the decomposition,the formation of various volatile products,the existence of counterintuitive homopolar reactions,and the formation of polymeric residues of complex composition,for example).Studies on destabilized AB have provided insights into several mechanistic aspects including the reaction intermediates,the decomposition pathways,and the nature of the residue forming upon the release of 1 and≥2 equiv.H_(2).We presently have a fairly good understanding of the mechanisms of decomposition of AB,which is discussed in more detail below.In that respect,this review focuses firstly on the complexity of thermal decomposition of neat AB,secondly on what we know with regard to thermal decomposition of destabilized AB,and thirdly on all outstanding questions.It is very important to have an excellent knowledge of the reaction mechanisms if technological progress is to be made with AB as a chemical hydrogen storage material.
基金supported by TUBITAK(Project No.218M181)and CAMPUS FRANCE PHC BOSPHORUS(Project No.42161TB).CACM.and U.B.D.want to acknowledge the CONACyT(Mexican National Council for Science and Technology)for the scholarship of CA.CM(2017-2021).
文摘Ammonia borane(NH_(3)BH_(3))is a reducing agent,able to trap and convert carbon dioxide.In the present work,we used a reactive solid consisting of a mixture of 90 wt.%of NH_(3)BH_(3)and 10 wt.%of palladium chloride,because the mixture reacts in a fast and exothermic way while releasing H2 and generating catalytic Pd0.We took advantage of such reactivity to trap and convert CO_(2)(7 bar),knowing besides that Pd0 is a CO_(2)hydrogenation catalyst.The operation(i.e.stage 1)was effective:BNH polymers,and B−O,C=O,C−O,and C−H bonds(like in BOCH_(3)and BOOCH groups)were identified.We then(in stage 2)pyrolyzed the as-obtained solid at 1250℃ and washed it with water.In doing so,we isolated cyclotriboric acid H_(3)B3O6(stemming from B2O3 formed at 1250℃),hexagonal boron nitride,and graphitic carbon.In conclusion,the stage 1 showed that CO_(2)can be‘trapped’and converted,resulting in the formation of BOCH_(3)and BOOCH groups(possible sources of methanol and formic acid),and the stage 2 showed that CO_(2)transforms into graphitic carbon.
