Beneficial effects of calcium chloride on glucose dehydration to 5-hydroxymethylfurfural in the presence of alumina as catalyst

•γ-Al2O3 with different acid-base properties is very active in glucose dehydration.•CaCl2 shifts the equilibrium toward α-glucopyranose, favoring the HMF formation.•The glucose isomerization to fructose is not predominant in presence of CaCl2.•Synergistic effect between CaCl2 and γ-Al2O3 provides HMF yield of 52% in 15min.•Alumina can be reused at least during three runs without regeneration.