NbSiBEA zeolites contained isolated framework mononuclear Nb(V) (Nb(0.7)SiBEA) and a mixture of framework mononuclear and extra-framework polynuclear Nb(V) (Nb(2.0)SiBEA) were prepared by two-step postsynthesis method as evidenced by XRD, NMR, DR UV-vis and FTIR. DR UV-vis showed that two types of framework mononuclear Nb(V) are present in Nb(2.0)SiBEA, while Nb(2.0)SiBEA mainly contained isolated mononuclear Nb(V) in the framework of zeolite and polynuclear Nb(V) in the extra-framework position. FTIR with pyridine and 2,6-di-tert-butylpyridine as probe molecules showed that major amount Lewis and weak Bronsted acidic sites are formed by incorporation of niobium in the framework of zeolites as mononuclear Nb(V). The catalytic properties of Nb-containing zeolites were investigated in tandem processes of ethanol conversion into 1,3-butadiene (gas-phase) and synthesis of unsymmetrical ethers from aromatic aldehyde and aliphatic alcohol (liquid-phase). It has been found that Nb0.7SiBEA catalyst, containing only isolated framework mononuclear Nb(V) is more active than Nb(2.0)SiBEA in the conversion of ethanol and ethanol/acetaldehyde mixture into 1,3-butadiene, MPV reduction of crotonaldehyde with ethanol and etherification of 4-methoxybenzyl alcohol with 2-butanol. The higher specific activity (turnover number/frequency) of Nb(0.7)SiBEA than Nb(2.0)SiBEA catalyst has been revealed for gas- and liquid-phase tandem processes. (C) 2016 Elsevier B.V. All rights reserved.