Space-confined preparation of high surface area tungsten oxide and tungsten nitride inside the pores of mesoporous silica SBA-15

• Space-confined synthesis of W2N in the pores of ordered mesoporous silica SBA-15.
• Two-step synthesis via mesoporous WO3 to phase-pure mesoporous W2N.
• Mesoporous tungsten nitride with small particle sizes and high surface area.
• Strong influence of template removal from WO3 before and after ammonolysis.
• Reduction of particle sintering during nitridation by order of template removal.

For the direct preparation of high surface area nitride materials, a lack of suitable precursors exists. Indirect preparation by gas phase nitridation (e.g. by ammonia) requires high temperatures and often results in sintering. The present work demonstrates that the space-confined preparation of W2N inside the pores of ordered mesoporous silica SBA-15 offers a possibility to reduce sintering phenomena and thus to obtain smaller particles, porous structures and a higher surface area material. The preparation was pursued in a two-step approach. First, WO3 was introduced into the channels of SBA-15 and second, ammonolysis was conducted for its conversion to W2N. When performed in the presence of the exotemplate, SBA-15 acts as a stabilizer and small W2N particles (6–7 nm) with a high specific surface area (40 m2 g−1) are obtained after template removal. When the template is, however, removed before nitridation, it cannot stabilize the W2N particles and enhanced sintering occurs.

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