the present invention is now described in more detail by reference to the following examples . the examples are only used for illustrating the present invention without limiting the scope of the present invention . 30 grams of vanadium oxide and 12 grams titanium oxide carrier ( kataleuna kl4500 - tl 1 . 6 ) were added into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was mixed with air then water vapor to give a mixture . the resultant mixture was continuously fed into the catalyst bed heated at a temperature of 260 ° c . the mole ratio of 3 - methylpyridine , oxygen contained in the air , and water was 3 - methylpyridine : oxygen : water of 1 : 30 : 70 , and the feed velocity of 3 - methylpyridine was 0 . 025 hr − 1 . on day 1 , a conversion of 3 - methylpyridine was 88 . 96 %, a selectivity of nicotinic acid was 75 . 65 %. after continuous reacting for 13 days , a conversion of 3 - methylpyridine reduced to 68 . 2 % and a selectivity of nicotinic acid was 78 . 74 %. in this reaction , the amount of nicotinic acid was determined by high performance liquid chromatography ( hplc ) by using c - 18 column as a separation column . the nicotinic acid was first sampled from reactor and rinsed with water , and then injected into hplc and quantified . also , un - reacted 3 - methylpyridine and carbon dioxide formed during reaction were quantified by gas chromatography ( gc ). after continuous reacting for 13 days , the catalyst was sampled and analyzed by electronic microscopy . its electronic microscopic photograph is shown in fig2 and 3 . the photograph of the catalyst before reaction is shown in fig1 . by comparing fig1 to 3 , it is known that the crystal size of the active ingredient ( vanadium oxide ) on the surface of the carrier gradually grow up while time passed . the increased crystal size is a possible reason of lowering conversion . the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 5 . 46 g of ammonium chromate were added into the solution and stirred for 30 minutes . into the resultant solution were added 91 . 41 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 700 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by scanning electronic microscopy and was found that the crystal size of the active ingredients on the surface of the carrier is from 80 to 100 nm , as shown in fig6 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 45 : 145 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 290 ° c . the feed speed of 3 - methylpyridine is 0 . 025 hr − 1 . the product was collected from output of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 96 . 82 %, a selectivity of nicotinic acid is 93 . 16 %, and a selectivity of carbon dioxide is 6 . 76 %. after continuous processing for 42 days , the catalyst was drawn out and examined by electronic microscopy . its microscopic photograph was shown in fig7 . from the figure , it is known that according to the present process for preparing nicotinic acid by using the present catalyst , the crystal size of the active ingredients on the surface of carrier did not vary while time passed . thus it demonstrates that the catalyst of the present invention exhibits excellent stability and longer lifetime . moreover , as the crystal size of the active ingredients on the surface of the carrier is controlled in the range of from 40 to 100 nm by adding transition metal oxide , its catalytic activity increases . thus a desired conversion and selectivity will be achieved by using less amount of catalyst . the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 3 . 44 g of ammonium molybdenate were added into the solution and stirred for 30 minutes . into the resultant solution were added 92 . 22 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 40 to 60 nm , as shown in fig8 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 40 : 170 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 300 ° c . the feed speed of 3 - methylpyridine is 0 . 021 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 90 . 21 %, a selectivity of nicotinic acid is 90 . 18 %, and a selectivity of carbon dioxide is 8 . 54 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 2 . 5 g of ammonium tungstate were added into the solution and stirred for 30 minutes . into the resultant solution were added 92 . 65 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 40 to 60 nm , as shown in fig9 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 37 : 160 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 285 ° c . the feed speed of 3 - methylpyridine is 0 . 028 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 92 . 83 %, a selectivity of nicotinic acid is 92 . 22 %, and a selectivity of carbon dioxide is 7 . 11 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 5 . 37 g of ammonium permanganate were added into the solution and stirred for 30 minutes . into the resultant solution were added 91 . 5 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by scanning electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 40 to 60 nm , as shown in fig1 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 20 : 150 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 305 ° c . the feed speed of 3 - methylpyridine is 0 . 025 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 95 . 67 %, a selectivity of nicotinic acid is 89 . 84 %, and a selectivity of carbon dioxide is 8 . 98 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 13 . 54 g of ferric nitrate were added into the solution and stirred for 30 minutes . into the resultant solution were added 92 . 31 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 700 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 60 to 80 nm , as shown in fig1 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 35 : 330 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 310 ° c . the feed speed of 3 - methylpyridine is 0 . 02 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 96 . 78 %, a selectivity of nicotinic acid is 93 . 13 %, and a selectivity of carbon dioxide is 5 . 56 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . into the resultant solution were added 92 . 27 g titanium oxide ( hembitec k - 03 ) and stirred for 30 minutes to obtain slurry containing ammonium meta - vanadate and titanium oxide . separately , 14 . 37 g of chromium nitrate was dissolved in water and slowly added into the slurry . the mixture was stirred for 1 hour , heated to evaporate water , and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 60 to 80 nm . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 40 : 170 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 300 ° c . the feed speed of 3 - methylpyridine is 0 . 021 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 93 . 54 %, a selectivity of nicotinic acid is 93 . 16 %, and a selectivity of carbon dioxide is 6 . 39 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 8 . 2 g of zinc sulfate were added into the solution and stirred for 30 minutes . into the resultant solution were added 92 . 68 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . after calcination , the catalyst was observed by electronic microscopy and found that the crystal size of the active ingredients on the surface of the carrier is from 40 to 60 nm . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 30 : 70 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 320 ° c . the feed speed of 3 - methylpyridine is 0 . 025 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 88 . 10 %, a selectivity of nicotinic acid is 88 . 32 %, and a selectivity of carbon dioxide is 9 . 25 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 6 . 43 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 5 . 46 g of ammonium chromate were added into the solution and stirred for 30 minutes . into the resultant solution were added 91 . 41 g titanium oxide ( degussa p - 25 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 700 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 40 : 175 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 305 ° c . the feed speed of 3 - methylpyridine is 0 . 02 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 91 . 06 %, a selectivity of nicotinic acid is 90 . 91 %, and a selectivity of carbon dioxide is 8 . 71 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 3 . 21 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 2 . 73 g of ammonium chromate were added into the solution and stirred for 30 minutes . into the resultant solution were added 95 . 71 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 700 ° c . to obtain the catalyst of the present invention , whose composition was shown in table 1 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 35 : 160 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 265 ° c . the feed speed of 3 - methylpyridine is 0 . 021 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 92 . 99 %, a selectivity of nicotinic acid is 88 . 75 %, and a selectivity of carbon dioxide is 10 . 54 %. the preparation of the catalyst of the present invention and the process for preparing nicotinic acid by using the catalyst 12 . 86 g of ammonium meta - vanadate were added into 500 ml water and the solution was heated at 70 ° c . to dissolve ammonium meta - vanadate . then , 4 . 99 g of ammonium tungstate were added into the solution and stirred for 30 minutes . into the resultant solution were added 80 . 30 g titanium oxide ( hembitec k - 03 ) and stirred for 1 hour . the mixture was heated to evaporate water and then calcined in an oven at a temperature of 600 ° c . to obtain the catalyst of the present invention , which composition was shown in table 1 . subsequently , 30 g of the prepared catalyst were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 30 : 160 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 285 ° c . the feed speed of 3 - methylpyridine is 0 . 05 hr − 1 . the product was collected at the outlet of the catalyst bed and analyzed by hplc and gc . it was found that a conversion of 3 - methylpyridine is 97 . 65 %, a selectivity of nicotinic acid is 92 . 58 %, and a selectivity of carbon dioxide is 7 . 23 %. 30 g of the catalyst prepared in example 2 were fed into a tube reactor having a diameter of 1 inch and a length of 5 centimeter to obtain a catalyst bed . 3 - methylpyridine was first mixed with air and then with h 2 o vapor and then continuously fed into the catalyst bed at a mole ratio of 1 : 40 : 170 ( 3 - methylpyridine : oxygen : h 2 o ) and where the bed temperature was controlled at 300 ° c . the feed speed of 3 - methylpyridine is 0 . 021 hr − 1 . at the outlet of the catalyst bed about 1 liter crude product was collected and analyzed by hplc and gc . it was found that the contents of 3 - methylpyridine and nicotinic acid were 0 . 0316 % and 2 . 91 %, respectively . the crude product was introduced into a distillation column in which a overhead temperature was set at 97 ° c . and the distillate was condensed in a volume of about 640 ml . the condensate was analyzed by hplc and found that the content of 3 - methylpyridine was 0 . 047 %. from the content of 3 - methylpyridine before and after distillation , its recovery rate was calculated and found as 95 %. the volume of bottom residue was 360 ml , which was crystallized to get nicotinic acid crystal and the crystal was analyzed . the purity of nicotinic acid by hplc and found being at least 99 %. from the above examples , it is known that by using the catalyst of the present invention , which is produced by controlling the crystal size of the active ingredient on the surface of carrier in a certain range through the addition of transition metal oxide , the nicotinic acid could be produced in a high yield and high selectivity . also , since the crystal size of the active ingredient on the surface of carrier is controlled in a certain range , the catalyst of the present invention exhibits a higher catalytic activity so that desired conversion and selectivity can be achieved by using a lower content of catalyst . while the present invention has been described with reference to the specific embodiments thereof , it should be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted without departing from the true spirit and scope of the invention . all such changes and modifications are intended to be within in the scope of the claims appended hereto .